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TEMPERATURE EFFECTS ON TIMING AND BUD DEVELOPMENT OF
COREOPSIS VERTICILLATA ‘MOONBEAM’ AND FLOWER INDUCTION OF
LONG-DAY PERENNIALS UNDER DIFFERENT NIGHT TEMPERATURES
By

Alison J. Frane

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements

for the degree of

MASTER OF SCIENCE
Department of Horticulture

1999

ABSTRACT
TEMPERATURE EFFECTS ON TIMING AND BUD DEVELOPMENT OF
COREOPSIS VERTICILLATA ‘MOONBEAM’ AND FLOWER INDUCTION OF
LONG-DAY PERENNIALS UNDER DIFFERENT NIGHT TEMPERATURES
By

Alison J. Frane

Effects of forcing temperature on ﬂowering Of Coreopsis verticillata
‘Moonbeam’ were recorded. Plants were initially cooled for twelve weeks and
then grown under 16-hr long days (4-h night interruption in the ﬁrst year) in
greenhouses set at 17, 20, 23, 26, and 29°C. Flower size, ﬂower number and
time to ﬂower decreased as temperature increased. The relationship between
ﬂower bud diameter, temperature and time to ﬂower was modeled as a sigmoid
logistic function. Models for time to visible bud (VB), ﬂower (FLW) and from VB
to FLW were developed using a linear function of rate of development.

The effectiveness of a four-hour night interruption (NI) to induce ﬂowering
in several species of long-day herbaceous perennials was tested at Six different
night temperatures. Eight herbaceous perennials were grown under natural
Short days augmented with a four-hour NI. Night temperatures were set at 2.5,
5, 10, 15, 20, and 25 °C with a day temperature of 25 °C for all treatments.
While some Species Showed an increase in the number of nodes developed prior
to ﬂower induction and a lower ﬂowering percentage at night temperature
treatments above 20° C, night temperatures as low as 3.9° C (4.9°C in the

second year) did not inhibit ﬂowering of any species.

To my brother, Alex

who always makes me laugh

ACKNOWLEDGMENTS

I want to thank my advisor, Dr. Will Carlson, for believing in me,
encouraging me when my Spirits lagged and for giving me the beneﬁt Of his
prodigious insight into human nature. I’d like to thank the other members of my
committee as well: Dr. Royal Heins for his helpful and informative guidance in
analyzing data and working on experiments; Dr. Art Cameron for his knowledge
and undying enthusiasm regarding perennials; and last but not least, Dr. Ken
Poff for asking the difﬁcult questions and saying what no one else will say.

I would also like to thank the other graduate students et al.: Emily Clough,
Beth Fausey, Leslie Finical, Antonis Kanavouras, Paul Koreman, Bin Liu, Mary-
Slade Morrison, Genhua Niu, Erik Runkle, Cara Wallace and Cathy Whitman for
their company, advice and support as well as Shiying Wang and Hiroshi Shimizu
for their help analyzing data.

Tom Wallace, Dan Tschirhart, and all the undergraduate workers at the
greenhouse were also invaluable in carrying out the experiments. It would not

have been possible without them.

TABLE OF CONTENTS

LIST OF TABLES ............................................... vii
LIST OF FIGURES ............................................. viii
LITERATURE REVIEW ........................................... 1
Photoperiod ............................................... 2
Perception of Photoperiod ............................... 4
Vemalization and Cold Treatment .............................. 6
Effects of Temperature on Rate ................................ 7
Thermocycles to Induce Flowering ............................ 11

Temperature Effects on Photoperiod Response in Long Day Plants . . . 13
Temperature Effects on Photoperiod Response in Short Day Plants . . 17

Conclusion ............................................... 19
Literature Cited ........................................... 21
MODELING TEMPERATURE EFFECTS ON TIME TO FLOWER AND BUD
DEVELOPMENT OF COREOPSIS VERTICILLA TA ‘MOONBEAM’ ........ 24
Abstract ................................................. 25
Introduction .............................................. 26
Materials and Methods ...................................... 28
Model Theory and Analysis .................................. 30
Rate Of progress model ................................ 3O
Bud development model ............................... 31
Results .................................................. 32
Rate of progress model ................................ 33
Bud development model calibration ...................... 33
Bud development model validation ....................... 34
Other plant qualities .................................. 34
Discussion ............................................... 35
Literature Cited ........................................... 38
Tables and Figures ........................................ 41
THE RESPONSE OF LONG-DAY HERBACEOUS PERENNIALS TO
A NIGHT-INTERRUPTION AT LOW NIGHT TEMPERATURES ........... 50
Abstract ................................................. 51
Introduction .............................................. 52
Materials and Methods ...................................... 53
Results and Discussion ..................................... 54
Literature Cited ........................................... 57
Tables and Figures ........................................ 58

APPENDIX A: NEW SPECIES SCREEN ............................. 62

Introduction .............................................. 63
Protocol ................................................. 64
Production lnforrnation ...................................... 65
Selected data for each species (in alphabetical order) ............. 68
APPENDIX B: EFFECTS OF FORCING TEMPERATURE .............. 106
Introduction ............................................. 107
Protocol ................................................ 108
Production lnfonnation ..................................... 1 09
Selected data for each species (in alphabetical order) ............ 110

vi

LIST OF TABLES

Table 1. Therrnoperiodic ﬂowering of Xanthium under normally non-inductive
photoperiods. Adapted from deZeew, 1957. .......................... 12

Table 2. Flowering of Gypsophila under SD or Nl lighting and different
temperature regimes. Adapted from Shillo and Halevy, 1982. ............ 14

Table 3. Number of days from the start of short day treatment to visible bud (top

number) and ﬂowering (bottom number) in poinsettia “Barbara Ecke Supreme.’ Adapted
from Langhans and Miller (1963) [n/a = event occurred, but the number of days was not
recorded; dash = event did not occur in 100 days] ......................... 17

Table 4. List of abbreviations and parameters. ........................ 41

Table 5. Nonlinear regression results from ﬁtting Eq. [4] to the full calibration
data set using actual temperature data for each measurement. The number of
observations in the data set was 421, and the R2 was .945. .............. 42

Table 6. Signiﬁcance of effect of temperature on height at ﬂower, number of
nodes added in forcing, ﬂower diameter, number of visible buds at ﬁrst ﬂower,
number of stalks, and number of visible buds per stalk at ﬁrst ﬂower for
Coreopsis verticillata ‘Moon beam’. .................................. 42

Table 7. Relationship between bud diameter, temperature, and time to ﬂower for
Coreopsis verticillata ‘Moonbeam’ according to Eq. 6. ................... 43

Table 7. Species used each year, number of plants per replicate, pot size at
arrivala, dates of arrival, start of treatment and end Of treatment. Plants were
held under 9-h SD in between arrival and start Of treatments. ............. 58

Table 8. Average daily temperatures and temperature during 4-h night
interruption (NI) for each treatment in the ﬁrst and second year. ........... 59

Table 9. New species screens 1997-1999. Production information, including
rating as a potted plant, cold and photoperiod recommendations, based on the
treatments given in this screen, and approximate weeks to ﬂower at 20°C. . . . 65

Table 10. Effects of Forcing Temperature. Production information, including
year included in experiment, weeks of cold given, approximate weeks to ﬂower at
17-29°C, and comments on plant quality and other Observations. Recom-
mended temperature range represented by bold numbers in the weeks to ﬂower
columns. ..................................................... 109

vii

LIST OF FIGURES

Figure 1. Parameters as ﬁt tO each temperature treatment individually, and the
lines ﬁt to them using Eq. [7] ﬁt to the whole data set. Parameter b is indicated
by closed circles and exponential function shown as a solid line, while parameter
c is indicated by Open circles and straight dashed line. .................. 44

Figure 2. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Coreopsis verticillata 'Moonbeam'. Solid lines represent predicted values from
the regression equations calculated from the ﬁrst year data (ﬁlled circles).
Second year data is represented by Open circles, and all error bars represent
standard deviation. Base temperature (Tb) and cumulative thermal time (CTT)
necessary to complete the indicated developmental stage were calculated from
the regression. ................................................. 45

Figure 3. Observed bud diameters at various times before ﬂower for each temp-
erature treatment from the calibration data set for C. verticillata 'Moonbeam'.
Line indicates bud diameter as modeled according to Eq. [7]. R2 = .945.. . . . 46

Figure 4. Predicted days to ﬂower for C. verticillata 'Moonbeam' from a given
bud diameter based on Eq. [6] vs. observed days to ﬂower from a given bud
diameter from the validation data set. Line represents 1:1 relationship. ..... 47

Figure 5. Slope and intercept of regression lines ﬁt to predicted vs. observed
second year data. Actual average temperatures from average date of visible

bud to average date of ﬂower were used. Slope is indicated by open circles and
corresponds to the axis on the left, while intercept is indicated by closed circles
and corresponds to the axis on the right. The gray line indicates where slope
and intercept would be for a 1:1 line. ................................ 48

Figure 6. Inﬂuence of forcing temperature on plant height, number of nodes
formed during forcing, diameter of open ﬂowers, number of ﬂowers, number of
stalks per plant, and number Of ﬂowers per stalk for Coreopsis verticillata
'Moonbeam'. Filled circles represent ﬁrst year data, open circles represent
second year data. Error bars Show standard deviation. ................. 49

Figure 7. Graphs a-d Show average number of nodes added from the

start of treatments to the ﬁrst ﬂower bud. Error bars show 95% conﬁdence
interval. Graphs e-h show ﬂowering percentage. Closed circles represent

data taken the ﬁrst year, while open triangles represent data taken the

second year. Linear trend (L) or quadratic trend (Q) nonsigniﬁcant (”3),

or signiﬁcant at P=0.05 (*), 0.01 (**), or 0.001 (***). ..................... 60

viii

Figure 8. Graphs a-d Show average number of nodes added from the

start of treatments to the ﬁrst ﬂower bud. Error bars Show 95% conﬁdence
interval. Graphs e-h show ﬂowering percentage. Closed circles represent

data taken the ﬁrst year, while open triangles represent data taken the

second year. Linear trend (L) or quadratic trend (0) nonsigniﬁcant (”5),

or signiﬁcant at P=0.05 (*), 0.01 (**), or 0.001 (***). ..................... 61

Figure 9. Effects Of photoperiod and cold treatment on Achillea 'Anthea' as
indicated. Error bars indicate 95% conﬁdence intervals. ................. 68

Figure 10. Effects Of photoperiod and cold treatment on Achillea ptarmica
‘The Pearl’ as indicated. Error bars indicate 95% conﬁdence intervals. ..... 69

Figure 11. Effects of photoperiod and cold treatment on Agastache 'Pink
Panther' as indicated. Error bars Show 95% conﬁdence intervals. ......... 70

Figure 12. Effects of photoperiod and cold treatment on Ajuga reptans 'Bronze
Beauty' as indicated. Error bars indicate 95% conﬁdence intervals. ........ 71

Figure 13. Effects of photoperiod and cold treatment on Anemone hupehensis
as indicated. Error bars show 95% conﬁdence intervals. ................ 72

Figure 14. Effects of photoperiod and cold treatment on Anemone sylvestn's as
indicated. Error bars show 95% conﬁdence intervals. ................... 73

Figure 15. Effects of photoperiod and cold treatment on Anemone vitifolia
'Robustissima' as indicated. Error bars Show 95% conﬁdence intervals. . . . . 74

Figure 16. Effects of photoperiod and cold treatment on Aster alpinus 'Goliath'
as indicated. Error bars Show 95% conﬁdence intervals. ................ 75

Figure 17. Effects of photoperiod and cold treatment on Aster dumosus as
indicated. Error bars Show 95% conﬁdence intervals. ................... 76

Figure 18. Effects of photoperiod and cold treatment on Aubn'eta 'Whitewell
Gem' as indicated. Error bars Show 95% conﬁdence intervals. ............ 77

Figure 19. Effects Of photoperiod and cold treatment on Campanula
portenschlagiana as indicated. Error bars Show 95% conﬁdence intervals. . . 78

Figure 20. Effects Of photoperiod and cold treatment on Clematis montana 'John
Paul ll' as indicated. Error bars show 95% conﬁdence intervals. .......... 79

Figure 21. Effects Of photoperiod and cold treatment on Clethra alnifolia 'Rosea'
as indicated. Error bars show 95% conﬁdence intervals. ................ 80

Figure 22. Effects Of photoperiod and cold treatment on Coreopsis auriculata
'Nana' as indicated. Error bars show 95% conﬁdence intervals. ........... 81

Figure 23. Effects of photoperiod and cold treatment on Coreopsis rosea as
indicated. Error bars Show 95% conﬁdence intervals. ................... 82

Figure 24. Effects Of photoperiod and cold treatment on Dianthus deltoides
'Shrimp' as indicated. Error bars show 95% conﬁdence intervals ........... 83

Figure 25. Effects of photoperiod and cold treatment on Dicentra eximia
'Luxuriant' as indicated. Error bars show 95% conﬁdence intervals. ........ 84

Figure 26. Effects of photoperiod and cold treatment on Echinacea purpurea
'Magnus‘ as indicated. Error bars show 95% conﬁdence intervals. ......... 85

Figure 27. Effects of photoperiod and cold treatment on Geranium 'Johnson’s
Blue' as indicated. Error bars show 95% conﬁdence intervals. ............ 86

Figure 28. Effects of photoperiod and cold treatment on Geum 'Mrs. Bradshaw'
as indicated. Error bars show 95% conﬁdence intervals. ................ 87

Figure 29. Effects of photoperiod and cold treatment on Gypsophila paniculata
'Happy Festival' as indicated. Error bars Show 95% conﬁdence intervals. . . . 88

Figure 30. Effects of photoperiod and cold treatment on Helenium 'ano' as
indicated. Error bars show 95% conﬁdence intervals. ................... 89

Figure 31. Effects of photoperiod and cold treatment on Helenium 'Red and
Gold Hybrid' as indicated. Error bars Show 95% conﬁdence intervals. ...... 90

Figure 32. Effects of photoperiod and cold treatment on Hemerocallis 'Rocket
City' as indicated. Error bars Show 95% conﬁdence intervals. ............ 91

Figure 33. Effects of photoperiod and cold treatment on Iris 'Sambo' as
indicated. Error bars Show 95% conﬁdence intervals. ................... 92

Figure 34. Effects of photoperiod and cold treatment on Lewisia cotyledon as
indicated. Error bars Show 95% conﬁdence intervals. ................... 93

Figure 35. Effects Of photoperiod and cold treatment on Lychnis coronaria
'Angel Blush' as indicated. Error bars show 95% conﬁdence intervals. ...... 94

Figure 36. Effects of photoperiod and cold treatment on Oenothera fruticosa
'Youngii-Lapsley' as indicated. Error bars show 95% conﬁdence intervals. . . 95

Figure 37. Effects of photoperiod and cold treatment on Polygonum afﬁne
'Dimity' as indicated. Error bars show 95% conﬁdence intervals. .......... 96

Figure 38. Effects Of photoperiod and cold treatment on Potentilla atrosanguinea
'Miss Willmott' as indicated. Error bars Show 95% conﬁdence intervals. ..... 97

Figure 39. Effects of photoperiod and cold treatment on Sidalcea 'Party Girls' as
indicated. Error bars Show 95% conﬁdence intervals. ................... 98

Figure 40. Effects of photoperiod and cold treatment on Stokesia Iaevis 'Klaus
Jellito' as indicated. Error bars Show 95% conﬁdence intervals. ........... 99

Figure 41. Effects Of photoperiod and cold treatment on Tanacetum 'Robinson's
Dark Crimson' as indicated. Error bars show 95% conﬁdence intervals. . . . . 100

Figure 42. Effects of photoperiod and cold treatment on Thalictrum
aquilegifolium as indicated. Error bars show 95% conﬁdence intervals. . . . . 101

Figure 43. Effects of photoperiod and cold treatment on Tiarella whenyi as
indicated. Error bars show 95% conﬁdence intervals. .................. 102

Figure 44. Effects of photoperiod and cold treatment on Tn'cyrtis hirta 'Miyazaki'
as indicated. Error bars Show 95% conﬁdence intervals. ............... 103

Figure 45. Effects of photoperiod and cold treatment on Veronica Iongifolia
'lcicle' as indicated. Error bars Show 95% conﬁdence intervals. .......... 104

Figure 46. Effects of photoperiod and cold treatment on Veronica Iongifolia 'Red
Fox' as indicated. Error bars Show 95% conﬁdence intervals ............. 105

Figure 47. Inﬂuence Of forcing temperature on time and rate toward ﬂowering for
Astilbe chinensis pumila in year 1. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 110

Figure 48. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Astilbe chinensis pumila in year 2. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (C'l'l') necessary to complete the
indicated developmental stage were calculated from the regression. ...... 111

Figure 49. Inﬂuence of forcing temperature on number of ﬂower buds, number of

nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Astilbe
chinensis pumila in year 1. Error bars show standard deviation. .......... 112

xi

Figure 50. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Astilbe
chinensis pumila in year 2. Error bars show standard deviation. .......... 113

Figure 51. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Campanula 'Birch Hybrid' in year 1. Lines represent predicted values from the
regression equations. AII error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 114

Figure 52. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Campanula 'Birch Hybrid' in year 2. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 115

Figure 53. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for
Campanula 'Birch Hybrid' in year 1. Error bars show standard deviation. . . 116

Figure 54. Inﬂuence of forcing temperature on number Of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Campanula 'Birch Hybrid'
in year 2. Error bars Show standard deviation. ....................... 117

Figure 55. Relationship between bud diameter and number of days before
ﬂower for Campanula 'Birch Hybrid' in year 1. Actual temperatures for the
indicated treatments are from average date of visible bud to average date of
ﬂower. ....................................................... 118

Figure 56. Relationship between bud diameter and number of days before
ﬂower for Campanula 'Birch Hybrid' in year 2. Actual temperatures for the
indicated treatments are from average date Of visible bud to average date of
ﬂower. ....................................................... 1 19

Figure 57. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Delphinium grandiﬂorum 'Blue Mirror' in year 1. Lines represent predicted values
from the regression equations. All error bars represent standard deviation. Base
temperature (Tb) and cumulative thermal time (CTT) necessary to complete the

indicated developmental stage were calculated from the regression ........ 120

Figure 58. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower

diameter, and plant height measured at ﬁrst ﬂower for Delphinium grandiﬂora
'Blue Mirror’ in year 1. Error bars Show standard deviation. ............. 121

xii

Figure 59. Relationship between bud diameter and number of days before
ﬂower for Delphinium grandiﬂora 'Blue Mirror' in year 1. Actual temperatures for
the indicated treatments are from average date Of visible bud to average date of
ﬂower. ....................................................... 122

Figure 60. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Geranium dalmaticum in year 1. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (T b) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 123

Figure 61. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Geranium dalmaticum in year 2. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (C'I‘l') necessary to complete the
indicated developmental stage were calculated from the regression. ...... 124

Figure 62. Inﬂuence Of forcing temperature on number Of ﬂower buds, number Of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for
Geranium dalmaticum in year 1. Error bars show standard deviation. ..... 125

Figure 63. Inﬂuence of forcing temperature on plant height, number of nodes
formed during forcing, diameter of Open ﬂowers, number of ﬂowers, number Of
stalks per plant, and number of ﬂowers per stalk for Geranium dalmaticum in
year 2. Error bars Show standard deviation ........................... 126

Figure 64. Relationship between bud diameter and number of days before
ﬂower for Geranium dalmaticum. First year data represented by circles, second
year data represented by triangles. Actual temperatures for the indicated
treatments from average date of visible bud to average date of ﬂower were 29.4,
25.8, 23.1, 19.9, and 176°C for the ﬁrst year and 28.7, 25.9, 22.2, 19.5, and
17.4°C for the second year. ...................................... 127

Figure 65. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Hemerocallis ’Stella de Oro' in year 2. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 128

Figure 66. Inﬂuence of forcing temperature on plant height, number Of nodes
formed during forcing, diameter of open ﬂowers, number of ﬂowers, number Of
stalks per plant, and number of ﬂowers per stalk for Hemerocallis 'Stella de Oro'
in year 2. Error bars show standard deviation. ....................... 129

xiii

Figure 67. Relationship between bud diameter and number of days before
ﬂower for Hemerocallis 'Stella de Oro' in year 2. Actual temperatures for the
indicated treatments are from average date of visible bud to average date of
ﬂower. ....................................................... 130

Figure 68. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Hibiscus 'Disco Belle Mix' in year 1. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 131

Figure 69. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Hibiscus 'Disco Belle Mix'
in year 1. Error bars show standard deviation. ....................... 132

Figure 70. Relationship between bud diameter and number Of days before
ﬂower for Hibiscus 'Disco Belle Mix' in year 1. Actual temperatures for the
indicated treatments are from average date of visible bud to average date of
ﬂower. ....................................................... 133

Figure 71. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Phlox paniculata 'Eva Cullum' in year 1. Lines represent predicted values from
the regression equations. All error bars represent standard deviation. Base
temperature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 134

Figure 72. Inﬂuence Of forcing temperature on time and rate toward ﬂowering for
Phlox paniculata 'Eva Cullum' in year 2. Lines represent predicted values from
the regression equations. All error bars represent standard deviation. Base
temperature (T b) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 135

Figure 73. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Phlox paniculata 'Eva
Cullum' in year 1. Error bars Show standard deviation. ................. 136

Figure 74. Inﬂuence Of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Phlox paniculata 'Eva
Cullum' in year 2. Error bars Show standard deviation. ................. 137

Figure 75. Inﬂuence Of forcing temperature on time and rate toward ﬂowering for
Phlox subulata 'Emerald Blue' in year 2. Lines represent predicted values from
the regression equations. All error bars represent standard deviation. Base
temperature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 138

xiv

Figure 76. Inﬂuence Of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Phlox subulata 'Emerald
Blue' in year 2. Error bars Show standard deviation. ................... 139

Figure 77. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Sedum 'Autumn Joy' in year 1. Lines represent predicted values from the
regression equations. All error bars represent standard deviation. Base temp-
erature (Tb) and cumulative thermal time (CTT) necessary to complete the
indicated developmental stage were calculated from the regression. ...... 140

Figure 78. Inﬂuence of forcing temperature on time and rate toward ﬂowering for
Sedum 'Autumn Joy' in year 2. All error bars represent standard deviation (too
small tO see). Base temperature (Tb) and cumulative thermal time (CTT) were
not calculated in this instance. .................................... 141

Figure 79. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Sedum
'Autumn Joy' in year 1. Error bars Show standard deviation. ............. 142

Figure 80. Inﬂuence Of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Sedum
'Autumn Joy' in year 2. Error bars Show standard deviation. ............. 143

LITERATURE REVIEW

Many plants develop and ﬂower in a seasonal pattern. It is advantageous
for a plant to ﬂower during a season in which it has adequate moisture and light,
and moderate temperatures. Just as important is the avoidance of stressful
conditions not conducive to growth and reproduction.

How do plants regulate developmental events to occur at the Optimal
time? If plants Simply responded to the presence or absence of favorable
weather conditions, accurate and consistent timing of developmental events
would be a rarity. In the natural environment, many plants use photoperiod to
regulate timing, as this is one Of the most reliable indicators of the time Of year.
In temperate zones, plants may also use the process of vemalization to detect
whether the unfavorable conditions of winter have passed.

Temperature during the growing season also has a marked effect on
development and timing. In a controlled environment, we can manipulate the
timing and magnitude Of ﬂowering for our own purposes by adjusting photoperiod
and temperature. This review will focus on photoperiodic response, modeling
temperature effects on rate of development, and how temperature can alter the

photoperiodic response.

Photomriod

The term photoperiod literally means period, or duration of the cycle, of
light. Thus photoperiod is the length Of the light period (also referred to as
daylength). Under natural conditions, however, the length of the light period is

directly related to the length of the dark period. While photoperiodic responses

2

could be dependent on the length of the light period or the length of the dark
period, or their relative lengths, it turns out that for most plants night length is
actually most important in determining photoperiodic response (Thomas and
Vince-Prue, 1984).

The photoperiodic responses of plants can be divided into three basic
categories, based on daylength. First, there are those plants that ﬂower only if
the photoperiod is short enough (night is long enough), or which ﬂower faster or
more profusely as days become shorter (nights become longer). These are
commonly called short-day plants (SDP). Other plants ﬂower only if the length of
the photoperiod is long enough (night is short enough), or their ﬂowering
response increases as the length of the photoperiod increases (night length
decreases). These are termed long day plants (LDP.) Finally, there are the
aptly named day neutral plants (DNP) in which ﬂowering response is not linked
to photoperiod at all. There also exist plants with dual daylength requirements
Le. a period of short days and then a period Of long days, or vice versa (SLDP
and LSDP respectively) (Thomas and Vince-Prue, 1997).

Plants that respond to photoperiod have been further divided into two
categories: qualitative or quantitative. A qualitative response (also known as an
obligate response) is characterized by a response to the quality of the
photoperiod — either inductive or not inductive (Thomas and Vince-Prue, 1997).
For instance, a qualitative LDP ﬂowers only when the photoperiod is longer than
a certain daylength, termed the critical photoperiod (Thomas and Vince-Prue,

1984) Below the critical photoperiod, an obligate LDP will not ﬂower. Similarly, a

3

qualitative SDP ﬂowers only when the photoperiod is shorter than a certain
daylength, also termed the critical photoperiod.

A quantitative, or facultative response, on the other hand, is characterized
by a ﬂowering response that varies with the quantity of light and darkness
(measured in hours) (Thomas and Vince-Prue, 1997, p.3.) For a quantitative
LDP, the longer the photoperiod, the greater the magnitude of ﬂowering
response (as measured by how fast or profusely the plant blooms.) A
quantitative SDP ﬂowers faster or more profusely with shorter photoperiods. A
quantitative plant will eventually bloom under any photoperiod (Thomas and

Vince-Prue, 1984)

Perception of Photoperiod

In order for plants to have any photoperiodic response, they must be able
to perceive daylength in some manner. This mechanism must also be fairly
precise if it is to accurately determine the time of year, especially at lower
latitudes, where the change in daylength throughout the year is relatively small.
For a long time, it was thought that plants measured the photoperiod by some
sort of “hourglass” mechanism, whereby a series of chemical steps was thought
to occur in the dark period. The plant would sense night length by how many
steps had been completed by the end of the night. This theory has largely been
replaced by a circadian rhythm theory (Thomas and Vince-Prue, 1997).

' The word circadian comes from the Latin for “around one day," a circadian

rhythm being a cyclic response throughout the natural 24 hr period of a day.

4

Organisms with circadian rhythms are not simply responding to the light and dark
periods that occur during that day, however. The rhythmic response is coupled
to an unseen internal oscillator, which continues even if these stimuli are taken
away, although usually not indeﬁnitely. The period of this rhythm, now referred
to as “free running,” in the absence of external stimuli, may be slightly more or
less than 24 hrs (Thomas and Vince-Prue, 1997)

This free running period cannot be started in an environment without
stimuli, however. Some event, usually a transition between light and dark, is
required. The circadian oscillator is said to be entrained to such an event, called
a zeitgeber, or time-giver. In order to accommodate the changing photoperiod
throughout the year, and still ensure that coupled responses occur at the
appropriate time of day, the entrainment of the oscillator is adjusted if the
zeitgeber occurs at some other phase of the cycle than the phase entrained to it
(Thomas and Vince-Prue, 1997).

In photoperiodic perception, the event coupled to the circadian oscillator is
thought to be a phase of relative sensitivity to light called the inducible phase
(4)..) In SDP, coincidence of light with ¢., would prevent ﬂowering, while in LDP, it
would induce ﬂowering. Light then plays two roles in the circadian rhythm of
photoperiodic perception: that of entralning the oscillator to the correct phase,
and that of inducing or inhibiting ﬂowering. This theory is based upon a system
of what is dubbed external coincidence, in other words, the coincidence of an
external stimulus (light) with a circadian oscillator (Thomas and Vince-Prue,

1997)

Other theories are based upon a system of internal coincidence -- the
interaction of two internal oscillators such that the correct phases of each
coincide. External stimuli, such as light would not serve a direct inducing or
inhibiting purpose, but would affect the entrainment of one or both oscillators so
that they are no longer in phase with each other. This type of system has not
been extensively explored for plants, however, and the internal coincidence

theory currently prevails (Thomas and Vince-Prue, 1997)

Vemalization and Cold Treatment

Vemalization is a process whereby exposure to cold temperatures is
required for ﬂoral induction. It should be distinguished from instances where the
cold treatment does not affect induction, but initiation and early development, as
in his Wedgewood, brussels sprouts and onion (Thomas and Vince-Prue, 1997).
In still other plants, a cold treatment is not required for induction, but merely
promotes subsequent ﬂower development. For example, in many fruit trees in
the Rosaceae, ﬂower buds are induced and initiated during the season prior to
bloom, and require a cold treatment to break dormancy (Gur, 1985).

Vemalization may be the only process necessary to induce ﬂowering, or
there may be a photoperiodic requirement as well after the vemalization process.
As with photoperiodic responses, plants can have an obligate or facultative cold
requirement to ﬂower. In some plants, a photoperiodic treatment, in particular a
SD treatment, is interchangeable with a cold requirement to induce ﬂowering .

All plants in which SD can substitute for a cold treatment are LDP, interestingly

6

enough. Thus, plants such as Campanula medium or Coreopsis grandiﬂora
which have this type of response could be classiﬁed as short-long—day plants
(SLDP) without cold, or simply LDP after cold (Napp-Zinn, 1984; Runkle, 1996;
Ketellapper and Barbaro, 1966). In other plants, such as Leucanthemum
vulgare, SD cannot fully substitute for a cold requirement, but SD during the cold

treatment can enhance the vemalization process (Heide, 1995).

Effects of Forcing Temperature on Rate

Temperature can affect plants in many different ways. It is well known
that higher temperatures increase rate of reactions in general, and more
speciﬁcally, developmental processes in living organisms. Temperature
responses are generally modeled by ﬁnding the amount of time necessary to
reach a developmental event, and converting it into a rate. Rates of
development in plants will generally have some optimum temperature (Tom)
where developmental rate reaches a maximum (Rmax), some base temperature
(T b) below Top, where the rate becomes zero, and some maximum temperature
(Tm) above Topt where the rate also becomes zero (Larsen, 1990).

Rate of development is Often modeled as a linear function of temperature
in the sub-optimal range (Whitman et. al., 1997; Yuan, 1998; Larsen, 1990), and
sometimes in the supra-optimal range. The slope of the line in the supra-optimal
range may have an equal but opposite slope to the line in the sub-optimal range,
creating a “roof" shaped graph (Pearson et. al. 1993), or it may have a different

slope, usually steeper.

The wider the range of temperatures selected, the less likely it is that one
will be able to model the data with a straight line. In cases like these, rate may
also be modeled by a quadratic equation (Larsen, 1990) as Wang et. al. (1998)
did with Hibiscus moscheutos. Brondum and Heins (1993) used an
asymmetrical “hoop” shaped curve to describe rates of development to ﬂower in
dahlia. Finally, yet another way to model rates above and below Top, is to use a
“double exponential” function where one exponential function describes the
response below Tom, and one describes the response above Topt (Larsen, 1990).
This also allows the model to take into account the possible asymmetry of the
response.

Pivotal to the process of modeling developmental events as a straight line
with respect to temperature are the concepts of Tb and degree-days (°d) or
thermal time (sometimes abbreviated as 8, or CTT: cumulative thermal time).
Using a linear model in the sub-optimal phase, rate of progress toward an event

is often described using an equation such as:

1 [1]
— = i+ ST
DTE

where DTE is the days to event (such as days to ﬂowering or the unfolding of a
leaf), iand s are constants representing intercept and slope respectively and T is

temperature. Using this model, base temperature (Tb) can then be calculated as:

—i [2]
Tb = "g‘

Thermal time is measured in units of degree-days, and represents the

average number of degrees above the base temperature experienced by the
plant on a given day. Thus a plant which experiences an average daily
temperature (ADT) one degree above it’s Tb accumulates one degree-day. Two
days at that ADT and it will accumulate two degree days, just as it will
accumulate two degree-days if it experiences one day at an ADT two degrees
above its Tb. Cumulative thermal time (CTT) indicates the number of degree-
days necessary for a plant to accumulate in order to achieve a given

developmental event, and can be expressed as:

[3]
CTT = 1
3

Base temperature (Tb) is never derived directly, but is always extrapolated
from the data, since when rate = 0, time to the event is inﬁnite. It is necessary to
know Tb in order to ﬁnd how many degree-days a plant is accumulating, or if it is
accumulating any at all. Then, knowing how fast degree-days are being
accumulated, it is possible to estimate time to an event at a given temperature.

Leaf unfolding rate (LUR) is often modeled to predict biomass production,
progress towards ﬂowering, or ﬁnal height. Models incorporating LUR have been
developed for sugar beets (Milford, et. al., 1985), and summer squash (NeSmith,
1997) to predict crop growth and yield. Such models can aid in cultivar selection
and management decisions such as pesticide sprays and harvesting schedules.

NeSmith (1997) found that by using thermal time rather than days after
sowing, four different cultivars of summer squash could be modeled using one

equation. This method of modeling differs from most others in that instead of

modeling using rates at different temperatures, he used C'l'l' for a crop grown at
varying temperatures. Leaf unfolding rates for Easter lily (Karlsson et. al., 1988),
and Chrysanthemum (Karlsson et. al., 1989) were found to have a linear
relationship to temperature.

For crops such as cut ﬂowers, bedding plants, perennials and ﬂowering
potted plants, there is much interest in the effects of temperature on time to
ﬂower. Song et. al. (1993) found that increasing average daily temperature
decreased days to ﬂower (from 17/15 to 25/23°C DIN temperature) for a variety
of cultivars of Platycodon grandiﬂorus. The timing of Easter lily crops is also
commonly controlled by adjusting temperature, higher temperatures causing
faster ﬂowering (Karlsson et. al., 1988). Whitman et. al. (1996) found that, for
Lavandula angustifolia ‘Munstead’, as temperatures increased from 15 to 27°C,
the number of days to ﬂower was reduced. Above 23°C, however, fewer plants
ﬂowered in the treatment group containing the smallest plants (7—9 nodes at
beginning of forcing), which suggests that perhaps 23°C is near to the optimum
ﬂowering temperature for ﬂowering in this species.

In the interests of modeling time to ﬂower, bud development has also
often been modeled, using measurements of bud length or diameter as growth
progresses and comparing the pattern and rate of expansion at different
temperatures. The most notable application of this type is the bud meter
concept developed by Healy and Wilkins (1984) whereby a model was
incorporated into a measuring tool. When the bud meter is held up to the bud,

the tip of the bud lines up with the number of days to ﬂower at several given

10

temperatures.

Fisher et. al. (1996) reﬁned the Easter lily bud meter by using a different
equation to model bud expansion. They found that an exponential model ﬁt the
data better and had fewer parameters than the original Healy-Wilkins model
which modeled bud expansion in two linear phases with a junction at the point
where bud length reached 6 mm.

Wang et. al. (1998) found that diameter of Hibiscus moscheutos buds
could be also be modeled using an exponential equation. While neither a bud
meter nor predictive tables were developed for Hibiscus, these could easily be

created from their model.

Thermocycles to Induce Flowering

A regular variation in temperature throughout the day, referred to as a
thennocycle (C. Mirolo et. al., 1990), can affect ﬂowering response in some
plants. Xanthium normally has a very restrictive photoperiodic requirement for
ﬂower induction. Xanthium is a qualitative SDP which requires at least a single
long dark period of 9 hr or greater to induce ﬂowering (deZeew, 1957). Even a
short light break in the middle of this long night prevents ﬂower initiation (Thomas
and Vince-Prue, 1997, p.15).

De Zeeuw (1957) found that it is possible to achieve ﬂowering in Xanthium

pennsylvanicum under normally non-inductive long day conditions by using

11

therrnocycles. He exposed the plants to a 16- hr photoperiod, half of which was

at 4°C and the other half at Table 1. Thermoperiodic ﬂowering of Xanthium
under normally non-inductive photoperiods.
26°C. One group of plants Adapted from de Zeeuw, 1957

 

Treatment dissection after:
(8hrs) (8hrs) (8hrs) 1 wk 2 wks

0f the light Period (T3) and one T1 26°C 26°C 26°C vegetative vegetative

received cold at the beginning

 

 

 

 

 

group received cold at the end T2 26°C 4°C 26°C Stage 3-5 Stage-l
T3 4°C 26°C 26°C stage8 6mm bud

T4 4°C 4°C 26°C vegetative vegetative

groups received 16 hr of light at (light) (light) (dark) stages as deﬁned
by Salisbury (1955)

 

 

 

 

of the light period (T2). Control

 

 

 

 

 

 

 

 

continual 4°C (T4) or continual
26°C (T 1 ). The dark period was kept at 26°C for all treatments. These
treatments lasted for four days before the plants were returned to normal long
days (temperature not speciﬁed). It was found that both T2 and T3 ﬂowered but
the ﬂower development proceeded more rapidly in the group that received cold
at the beginning of the light period (T3). Treatment 4 was not expected to ﬂower
as it had been shown that Xanthium has a requirement for a certain amount of
high light at high temperatures. The experiment was repeated with the
treatments lasting only two days, with similar results, but slower ﬂower
development.

Mirolo (1990) repeated T3 with a slight variation. He used Xanthium
struman’um and had the warmer temperature set at 23°C. He conﬁrmed that
Xanthium could be induced to ﬂower under non-inductive photoperiods by using
therrnocyoles. He also conﬁrmed de Zeeuw’s ﬁnding that only two such

therrnocycles were necessary to cause induction, but that ﬂowers developed

12

 

faster with more therrnocycles.

Knowing that gibberellic acid has a promotive effect only on induced
Xanthium plants, Mirolo also tested to see whether this would be the case with
therrnocyclicly induced Xanthium. He found that found that two then'nocycles
with one 5X10“ M treatment per day of gibberellic acid to the roots was
comparable to normal short-day induction of Xanthium, in terms of the
differentiation of the terminal male inﬂorescence in the two weeks following
induction.

It is unclear what mechanism these therrnocycles would be affecting in the
induction of Xanthium. It could be hypothesized that the relatively cold
temperature during the day either prevents the plant from perceiving that period
as light, or prevents or slows the transmission of the resulting Signal, causing the

plant to develop as if it had experienced a long night.

Temperature Effects on Photomriod Response of Long Day Plants

In some cases, cold temperatures can prevent or reduce normal ﬂowering
response to an inductive photoperiod. Shillo and Halevy (1982) carried out a
series of experiments on the long day plant, Gypsophila paniculata (Baby’s
Breath), cv. ‘Bristol Fairy. To investigate the interaction between temperature
and photoperiod, they placed plants under two photoperiods, either SD (8 hr) or
L0 (16 hr), and one of three temperature regimes, 27/22, 22/17, 17/12°C
day/night.

They found that none of the plants ﬂowered under short days, but under

13

long days, the percentage of plants ﬂowering depended strongly on the
temperature, although there was no temperature at which all plants failed to

Table 2' Flowering of Gypsophila ﬂower. The higher the temperature, the

under SD or NI lighting and different .
temperature regimes. Adapted from greater was the promotIve effect of the long

Shillo and Halevy, 1982

 

 

 

 

 

 

 

 

 

. photoperiod. This agreed with ﬁeld
Temp, (°C) FlowerIng plants (°/o)
day/night SD LD observations that at low night temperatures
27/22 0 33 during the winter, plants often failed to
22,17 0 12 ﬂower. They also concluded that high night

temperatures were only required for initiation and the early stages of elongation
and bud formation. This was inferred from the fact that plants started earlier in
the fall ﬂowered during the winter without additional heat, while those planted
later did not ﬂower until spring.

Hicklenton et. al. (1993) later conﬁrmed experimentally that it is indeed the
night temperature which is the limiting factor in ﬂower induction. They tested two
cultivars of Gypsophila paniculata (“Bristol Fairy’ and ‘Bridal Veil’) to determine
the optimum irradiance and night temperature for each. Night temperature
treatments were 8, 12, 16, or 20°C. Day temperature was at 20°C for all
treatments. Half of the plants received 710 umol-s“-m'2, and half receive 450
IImol~S"-m'2 for 9 hrs, resulting in daily light integrals of 23 and 14.6 mol-m‘z.
They found that at low night temperatures ‘Bristol Fairy’ often failed to initiate
ﬂower buds (only 33% of the plants ﬂowered at a night temperature of 8°C). This
occurred at both irradiances tested, but the effect was more marked at 450

umol-S'1-m'2. Percentage of plants ﬂowering of cv. “Bridal Veil’ was almost

14

completely unaffected by light level or night temperature.

In another experiment (Shlomo et. al., 1985), it was found that gibberellin
treatments could substitute for this high night temperature requirement under
long days. They grew G. paniculata “Bristol Fairy’ plants under short (10 hr) or
long (4 hr day extension) photoperiod. Plants were sprayed twice weekly (11
times) with GA at varying concentrations. Plants receiving LD treatment were
sprayed with concentrations of 0, 125, 250 or 500 mg-l", while plants receiving
SD treatment were sprayed with concentrations of 0 or 250 mg-l". All plants in
the LD treatment that received GA ﬂowered, whereas only 33% ﬂowered under
LD without GA. Number of stems per plant and total weight of ﬂowering stems
per plant increased while time to ﬂower decreased with increasing GA
concentration. No plants under SD ﬂowered regardless of GA treatment,
although there were some partially elongated stems which resulted in “blind”
shoots or which had rosette-like vegetative growth at the end.

GA substitution for the high night requirement for ﬂowering under long
days is interesting to note because unlike many other LDP, gibberellin
treatments cannot substitute for the long-day requirement itself in Gypsophila
paniculata (Shillo and Halevy, 1982; Shlomo et. al., 1985). As with Xanthium,
gibberellin enhances the ﬂowering response, but cannot substitute for the
photoperiodic requirement itself. Also like Xanthium, the interaction of
temperature and photoperiod could be related to the lack of perception of the
Iight‘administered during the drop in temperature. On the other hand, it could

also be related to a lack of realization of the photoperiodic response.

15

Brendum and Heins (1993) reported an interaction between temperature
and photoperiod in tuberous root formation, lateral shoot count, lateral shoot
length, and primary shoot length of Dahlia pinnata ‘Royal Dahlietta Yellow’. They
created twenty-four temperature x photoperiod factorial treatments with four
temperatures, set at 15, 20, 25 or 30°C, and six photoperiods of 10, 12, 14, 16,
20, or 24 hrs. At lower temperatures and shorter photoperiods, tuberous root
formation was promoted: above 14 hrs or 25°C, there was little to no tuberous
root formation. The number of lateral Shoots increased with photoperiod up to
14 hrs. At photoperiods above 14 hrs, there were fewer lateral shoots at 25°C,
than at 15 or 20°C. Lateral shoot length increased with photoperiod from 10 to
14 hrs, while above 14 hrs, shoot length was more dependent on temperature —
the higher the temperature, the shorter the lateral shoots.

Temperature and photoperiod also interacted to affect some aspects of
ﬂowering. Flower development was more strongly affected by temperature,
although photoperiod did have some effects. For instance, at 25°C, ﬂower buds
formed at photoperiods greater than 14 hrs aborted, while at 30°C, no ﬂower
buds were formed at all (Brendum and Heins, 1993).

The interaction between temperature and photoperiod for overall
production of dahlia is very complex because of the many variables of plant
development that are affected. Variation in photoperiod often seems to affect
the magnitude of the response to temperature. Brendum and Heins concluded
from this study that there are very narrow temperature and photoperiod ranges

for optimum production of Dahlia pinnata ‘Royal Dahlietta Yellow’, namely,

16

photoperiods between 12 and 14 hrs and temperatures around 20°C. Optimum
was deﬁned as producing plants of a satisfactory height that develop quickly and

have many ﬂower buds.

Temmrature Effects on Photogeriod Resgonse in Short Day Plants

In some SDP, critical photoperiod is dependent on temperature. For
example, in poinsettia or Chrysanthemum, raising temperature causes the critical
photoperiod to change. Langhans and Miller (1963) subjected poinsettias
(Euphorbia pulcherrima) to three different temperature regimes (60, 70 and
80°F), and photoperiods between 8 hrs and 12 hrs (see table) for varying
numbers of days before returning them to 13 hr photoperiods.

They found that as temperature increased, the photoperiod required for

Table 3. Number of days from the start of short day treatment to visible bud (top
number) and ﬂowering (bottom number) in poinsettia ‘Barbara Ecke Supreme.’ Adapted
from Langhans and Miller (1963) [n/a = event occurred, but the number of days was not
recorded; dash = event did not occur in 100 days]

 

Temperature (°F) and photoperiod (hours)

#Of 0 O 0
short 60 F 70 F I 80 F
days 8 10 11‘/2 12 8 10 101/2117: 12' 8 I874 9 9% 10 12
20 40 41 40 53 55 49 49 -- -- n/a 69 69 64 62 --
83 88 93 93 -- -- —- -- -- -- -- -- -- -- --

303839404332343338574240475271--
87898793626262---—---—............

403538374533323241554042444045-—-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

85 88 87 93 62 62 61 -- -- 62 -- -- .... .. ...
50 . 37 41 41 44 34 32 35 40 48 41 38 44 44 53 --
87 87 87 99 62 61 63 64 -- 62 62 72 n/a 74 --

 

17

induction became more restrictive, and that different conditions were required for
ﬂower initiation than for ﬂower development. For example, as temperature and
photoperiod increased and number of short days decreased, more plants
produced buds which never produced ﬂowers. This suggests that shorter
photoperiods, lower temperatures, and more days of inductive treatments are
required for ﬂower development than for ﬂower induction.

Poinsettia could be termed “short day-shorter day plants”, with respect to
ﬂowering, meaning that they are SDP for which the critical photoperiod gets
shorter for subsequent ﬂower development. Horticulturally they are often grown
using blackcloth to artiﬁcially shorten photoperiod until natural daylength is short
enough to satisfy the requirement for induction/initiation. Continued shortening
of days would naturally satisfy the more restrictive requirement for ﬂower
development.

In more recent research at Michigan State University, it has been shown
that it is night temperature, rather than average daily temperature, which is
actually a limiting factor for ﬂowering in poinsettia (Heins, 1990). Poinsettia were
grown at six different night temperatures and six different day temperatures,
ranging from 14-29°C. Heins (1990) found that at night temperatures above
26°C, no plants ﬂowered, regardless of the day temperature.

A similar interaction between temperature and photoperiod was reported
in the SDP Dendranthema grandiﬂora (formerly Chrysanthemum mon'folium)
(Cathey, 1957). Several varieties of Chrysanthemum were subjected to seven

photoperiodic treatments in combination with three minimum night temperatures.

18

Like Langhans and Miller, Cathey found that the requirements for initiation and
ﬂowering differed and that they were both affected by interactions between
temperature and photoperiod. Critical night length for ﬂower development
increased (became more restrictive) as temperature increased. However, the
night length required for ﬂower initiation decreased (became less restrictive) as
temperature increased. This resulted in a greater difference between the critical
night length for initiation and ﬂowering as temperature increased. At 50°F (the
lowest temperature tested) there was no difference between critical night length
for initiation and development of the ﬂower.

lson and Humphries (1984) reported that for the qualitative SDP
Stylosanthes guianensis var. guianensis cv. Schoﬁeld grown at a photoperiod
marginal for ﬂowering (12 — 11.75 hrs), ﬂoral initiation was promoted by low night
temperatures (25/16°C or 25/20°C D/N) temperatures and inhibited by high
(35°C) day temperatures. These results are similar to some of the results in
Chrysanthemum and poinsettia. Several other SDP, namely Chenopodium,
Lemna and Pharbitis, also have critical photoperiods which are dependent on

temperature (Thomas and Vince-Prue).

anclugion

According to the evidence presented in this paper, plants can be placed
into two general categories: those where temperature seems to affect the
perception of light, and those in which critical photoperiod is dependent on

temperature. The mechanisms of photoperiodism are not well understood,

19

despite many years of research on the subject, thus these mechanisms can only
be studied by observing plant responses. This complicates any discussion of
interactions between the phenomenon of photoperiodism and growing
temperature.

Whatever the mechanisms involved, a knowledge of the existence of
interactions between temperature and photoperiod can help us to model plant
responses, and understand seeming irregularities in plant development.
Hopefully this will also lead us to a better understanding of plant physiological

processes in general.

20

Literature Cited

Brandum, J.J. and RD. Heins. 1993. Modeling temperature and photoperiod
effects on growth and development of dahlia. J. Amer. Soc. Hort. Sci.
1 18:36-42.

Cathey, HM. 1957. Chrysanthemum temperature study. F. The effect of
temperature upon the critical photoperiod necessary for the initiation and
development of ﬂowers of Chrysanthemum mon’folium. Proc. Amer. Soc.
Hort. Sci. 69:485-491.

Fisher, P.R., J.H. Lieth and RD. Heins. 1996. Modeling ﬂower bud elongation
in Easter lily (Lilium Iongiﬂomm Thunb.) in response to temperature.
HortScience 31:349-352.

Gur, A. 1985. Rosaceae - deciduous fruit trees, p. 355-389. In: A.H. Halevy
(ed). CRC Handbook of Flowering. CRC Press, Inc., Boca Raton.

Healy, W.E and HF. Wilkins. 1984. Temperature effects on ‘Nellie White’ ﬂower
bud development. HortScience 19:843-844.

Heide, OM. 1995. Dual induction control of ﬂowering in Leucanthemum
vulgare. Physiologia Plantarum 95:159-165.

Heins, RD. 1990. Choosing the best temperature for growth and ﬂowering.
Greenhouse Grower.

Hicklenton, P.R., S.M. Newman and L.J. Davies. 1993. Night temperature,
photosynthetic photon ﬂux, and long days affect Gypsophila paniculata
ﬂowering. HortScience 28:888-890.

lson, R.L. and LR. Humphries. 1984. Day and night temperature control of
ﬂoral induction in Stylosanthes guianensis var. Guianensis cv. Shoﬁeld.
Annals of Botany 53:207-211.

Kartsson, M.G., R.D. Heins and J.E. Erwin. 1988. Quantifying temperature-
controlled leaf unfolding rates in ‘Nellie White’ Easter lily. J. Amer. Soc.
Hort. Sci. 113:70-74.

Karlsson, M.G., R.D. Heins, J.E. EI'WII'I, R.D. Berghage, W.H. Carlson and J.A.
Biembaum. 1989. Temperature and photosynthetic photon ﬂux inﬂuence
‘ Chrysanthemum shoot development and ﬂower initiation under short-day
conditions. J. Amer. Soc. Hort. Sci. 114:158-163.

21

Ketellapper, H.J. and A. Barbaro. The role of photoperiod, vemalization and
gibberellic acid in ﬂoral induction in Coreopsis grandiﬂora Nutt. Phyton.
23(1): 33-41.

Langhans, R.W. and RC. Miller. 1963. Inﬂuence of daylength, temperature,
and number of short days on the ﬂowering of poinsettia (Euphorbia
pulchem'ma). Proc. Amer. SOC. Hort. Sci. 75:753-760.

Larsen, R.U. Plant growth modelling [Sic] by light and temperature. Acta Hort.
272:235-242.

Milford, G.F.J., T.O. Pocock and J. Reily. 1984. An analysis of leaf growth in
sugar beet. I. Leaf appearance and expansion in relation to temperature
under controlled conditions. Ann. Appl. Biol. 106, 163-172.

Mirolo, C., M. Bodson, and G. Bemer. 1990. Floral Induction of Xanthium
struman'um In Long
Days. Ann. Bot. 66, 475-477.

Napp-Zinn, K. 1984. Light and vemalization, pp. 75-88. In: D. Vince-Prue, B.
Thomas and K.E. Cockshull (eds.). Light and the Flowering Process.
Academic Press, London.

Pearson, S., P. Hadley, and AB Wheldon. 1993. A reanalysis of the effects of
temperature and irradiance on time to ﬂowering in Chrysanthemum
(Dendranthema grandiﬂora). J. Hort. Sci. 68:89-97.

Roberts, E.H. and R.J. Summerﬁeld. 1987. Measurement and prediction of
ﬂowering in annual crops, p. 17-50. In: J. G. Atherton (ed.). Manipulation
of Flowering. ButteIworths, London.

Runkle, ES. 1996. The effects of photoperiod and cold treatment on ﬂowering
of twenty-ﬁve species of herbaceous perennials. MS Thesis, Dept. of
Horticulture, Michigan State Univ., East Lansing.

Shlomo, E., R. Shillo, and A. Halevy. 1985. Gibberellin substitution for the high
night temperatures required for the long-day promotion of ﬂowering in
Gypsophila paniculata L. Scientia Hort. 26: 69-76.

Shillo, R. and AH. Halevy. 1982. Interaction of photoperiod and temperature in
ﬂowering-control of Gypsophila paniculata L. Scientia Hort. 16:385-393.

Song, C.Y., S.K. Chung, M.S. Rob and RH. Lawson. 1993. Temperature

inﬂuences growth and ﬂowering of Platycodon. J. Kor. Soc. Hort. Sci.
34(6):446-453.

22

Thomas, B. and D. Vince-Prue. 1997. Photoperiodism In Plants. Academic
Press, San Diego.

Thomas, B. and D. Vince-Prue. 1984. Juvenility, photoperiodism and
vemalization. In Advanced Plant Physiology. Wilkins, M. 8., ed. Pitman
Publ., London. pp. 408-439.

Wang, 8., RD. Heins, W.H. Carlson and AC. Cameron. 1998. Modeling the
effect of temperature on ﬂowering of Hibiscus moscheutos. Acta Hort.
456:161-169.

Whitman, C.M., R.D. Heins, A.C. Cameron and W.H. Carlson. 1996. Cold
treatments, photoperiod, and forcing temperature inﬂuence ﬂowering of
Lavandula angustifolia. HortScience, 31 :1 150-1 153.

Whitman, C.M., R.D. Heins, A.C. Cameron and W.H. Carlson. 1997. Cold
treatment and forcing temperature inﬂuence ﬂowering of Campanula
carpatica ‘Blue Clips’. HortScience 32:861-865.

Yuan, M., W.H. Carlson, R.D. Heins and AC. Cameron. 1998. Effect of forcing
temperature on time to ﬂower of Coreopsis grandiﬂora, Gaillardia
xgrandiﬂora, Leucanthemum xsuperbum and Rudbeckia fulgida.
HortScience 33:663-667.

de Zeeuw, D. 1957. Flowering of Xanthium under long day conditions. Nature
180:558.

23

MODELING TEMPERATURE EFFECTS ON TIME TO FLOWER AND BUD

DEVELOPMENT OF COREOPSIS VERTICILLA TA ‘MOONBEAM’

24

Abstract

Effects of forcing temperature on ﬂowering of Coreopsis verticillata L.
‘Moonbeam’ were recorded. Plants were initially cooled for twelve weeks and
then grown under 16-hr long days (4-h night interruption in the ﬁrst year) in
greenhouses set at 17, 20, 23, 26, and 29°C. Flower size, ﬂower number and
time to ﬂower decreased as temperature increased. The number of nodes
added from the start of forcing to ﬂower was unaffected by temperature. The
relationship between ﬂower bud diameter, temperature and time to ﬂower was
modeled as a sigmoid logistic function. Models for time from start of long day
forcing at each temperature to visible bud (VB), ﬂower (FLW) and from V8 to
FLW were developed based on a linear function of rate of development. The
optimum temperature for time to ﬂower for C. verticillata ‘Moonbeam’ was at least
29°C, although plant quality factors such as ﬂower diameter and ﬂower number

were greater at lower temperatures.

25

Introduction

Accurate scheduling is just as important as a high quality crop in the
ﬂoriculture industry. Forcing temperature is one of the factors affecting both
timing of ﬂowering as well as attributes such as plant height, ﬂower number and
ﬂower size which contribute to plant quality (Arrnitage, 1990; Pearson et. al.,
1995; Shvarts et. al. 1997; Whitman et. al., 1996; Yuan et. al., 1998).

Predictive tools such as bud meters and tables can be derived from
models to assist growers in precisely timing crops. For example, Easter lilies are
commonly timed using temperature models for leaf unfolding and bud
development (Karlsson et. al., 1988; Fisher et. al., 1996). Similar models have
been developed for plants throughout the horticultural trade for annuals such as
Begonia (Karlsson 1992), ﬂowering pot crops such as African violet (Faust and
Heins, 1993), cut ﬂowers (Criley, 1995) and vegetables (NeSmith, 1997).

Perennials are often sold in a vegetative state. Since selling plants in
bloom increases both their value and desirability (Harrison, 1996), there is
increased interest in forcing perennials to ﬂower. Scheduling a plant to ﬂower on
a particular date requires the proper ﬂower induction environment as well as
appropriate temperatures for correct timing. This requires knowledge of the
relationship between forcing temperature and time to ﬂower. Some models have
been developed relating temperature to time of ﬂowering for perennials, among
these are Campanula, Coreopsis, Gaillardia, Leucanthemum and Rudbeckia
(Whitman et. al., 1997; Yuan, 1998). However, few bud development models

have been developed for herbaceous perennials.

26

Temperature responses are generally modeled by ﬁrst observing times
taken to an event, then converting to rates. Rates of development in plants, as
for any biological process, will always have some optimum temperature (Tom)
where developmental rate reaches a maximum (RM), some base temperature
(T b) below Top, where this rate becomes zero, and some maximum temperature
(Tm) above Topt where this rate also becomes zero (Larsen, 1990).

Rate is often modeled as a linear function of temperature in the sub-
optimal range (Whitman et. al., 1997; Yuan, 1998; Larsen, 1990), and
sometimes in the supra-optimal range. The slope of the line in the supra-optimal
range may have an equal but opposite slope to the line in the sub-optimal range,
creating a “roof” Shaped graph (Pearson et. al. 1993), or it may have a different
slope, usually steeper. Rate may also be modeled by a quadratic equation
(Larsen, 1990) as Wang (1998) did with Hibiscus moscheutos. Brondum and
Heins (1993) used an asymmetrical “hoop” shaped curve to describe rates of
development to ﬂower in dahlia. Finally, yet another way to model rates above
and below Top, is to use a “double exponential” function where one exponential
function describes the response below Tom, and one describes the response
above Topt (Larsen, 1990). This also allows the model to take into account any
asymmetry of the response.

Coreopsis verticillata, also known as Threadleaf Coreopsis, is well known
for its outstanding performance In warm sunny areas of the garden. It’s ﬁne
foliage helps reduce water loss, making it quite drought resistant, and it is hardy

over most of the United States, from zones 3-9 (Arrnitage, 1989; Nau, 1996).

27

Flowers are 1-2” across, in varying shades of clear yellow, with eight ray ﬂorets
extending out from a yellow center disk. Most varieties will rebloom sparsely if
cutback after the initial ﬂush in June and early July, but ‘Moonbeam’ will often
produce its pale yellow ﬂowers continuously through October (Arrnitage, 1989).
In 1992, ‘Moonbeam’ was chosen as the Perennial Plant of the Year by the
Perennial Plant Association (Nau, 1996). It’s popularity, garden performance,
and wide range make it an excellent candidate for scheduled forcing.

Hamaker (1998) showed that Coreopsis verticillata ‘Moonbeam’ is an
obligate long-day plant for ﬂowering and that a cold treatment increased ﬂower
number and hastened ﬂowering. Our objectives were to 1) quantify the inﬂuence
of temperature on time to VB and time to FLW, 2) develop a model relating bud
size and temperature to time to ﬂower, and 3) quantify other effects of forcing
temperature on plant quality, including ﬂower number, ﬂower size and plant

height for C. verticillata ‘Moonbeam’.

Materials and Methods

First year. On October 15, 1996, propagules of Coreopsis ven‘icillata
‘Moonbeam’ were received in 70-cell ﬂats from Green Leaf Enterprises (Leola,
Pa.). Plants were immediately placed in a growth chamber set at 5° C under a 9-
hr photoperiod at ~10 umol rn'2 3'1 provided by cool white ﬂuorescent bulbs
(VHOF96T12: Philips, Bloomﬁeld NJ.) as measured by a Ll-COR quantum
sensor, model LI-189 (LI-COR, Lincoln, Neb.).

After 12 weeks in the cooler, plants were transplanted into 13-cm square

28

containers (1.1L), and ten plants per temperature treatment were grown under
long days in greenhouses set at 17, 20, 23, 26, and 29°C (actual temperature
averages from the start of forcing to average date of FLW for each treatment
were 17.3, 19.7, 23.5, 26.1, and 293°C respectively). Long days consisted of
natural photoperiods plus a 4-hour night interruption from 1000 to 0200 hours,
provided by 60-W incandescent lights at 3 to 5 umol rn'2 s‘1 as measured by a
quantum sensor (LI-COR).

Temperature in each greenhouse was recorded continually with a CR—10
datalogger (Campbell Scientiﬁc, Logan, Utah). Actual average daily
temperatures were determined and used in all calculations rather than set point
temperature. One representative ﬂower bud was chosen from among those
present at the ﬁrst incidence of visible buds on each plant, and its diameter was
measured every three to ﬁve days thereafter. Dates of visible bud and anthesis
were recorded. At anthesis, plant height, and number of ﬂower buds were
recorded.

Second year. On October 2, 1997, propagules of Coreopsis verticillata
‘Moonbeam’ were received in 128-cell ﬂats from Center Greenhouse, Inc.
(Denver, 00.). These received the same cold and forcing temperature
treatments as in the model-development experiment, but the long-day treatment
was delivered using a 16-hr day-extension provided by 400W high-pressure
sodium lamps at 50 umol m'2 S". These same lights provided 50 umol rn'2 S'1
supplemental light, when ambient light levels in the greenhouse dropped below

400 umol rn'2 S". Actual temperature averages from the start of forcing to

29

average date of FLW in the second year were 17.7, 19.9, 23.0, 26.1, and 294°C
for the 17, 20, 23, 26, and 29°C treatments, respectively. Vapor pressure deﬁcit
(VPD) control was instituted in the second year, and maintained at approximately
0.7 kPa. This was accomplished by monitoring wet and dry bulb temperature,
calculating VPD, and activating steam injection when the VPD increased above
the threshold. In addition to the data collected in the ﬁrst year, ﬂower diameter

and the number of ﬂowering stalks were also recorded.

Model Theog and Analysis

Rate of progress model. Progress toward a developmental event such as
ﬂowering may be modeled as a linear increase with temperature up to a certain
point, at which developmental rate levels off at an optimum, and then decreases
(Roberts and Summerﬁeld, 1987). In the sub-optimum temperature linear phase,

this relationship can be described as follows:

1 . [1]
—=I+ST
DTE

where DTE is the days to event (such as days to ﬂowering, days to VB or days
from VB to FLW), iand s are constants representing the intercept and slope
respectively of a straight line, and T is temperature. Abbreviations and
parameters used in models are listed in Table 4. By manipulating Eq. [1], base

temperature (Tb) for a given developmental event can be calculated as:

_- 2
T=_’ []
s

and cumulative thermal time (CTT) in degree-days necessary to achieve the

30

event can be calculated as:

3]
CTT:—1 [
S

For the analysis, rates were calculated from the number of days from
force to VB, VB to FLW and force to FLW (1/DTE) and Eq. [1] was ﬁt to these
data points. Model validation DTE were compared with DTE predicted by the
model produced from the ﬁrst-year data.

Bud development model. A sigmoid logistic function was used to describe

the increase in bud diameter from visible bud to ﬂower:

_ a [4]
— 1+ bec"f 4)

where bud diameter (B in mm) at time t (days) depends on the number of days to

B

 

ﬂowering (at time t,, in days).

The parameter a deﬁnes an asymptote which indicates a theoretical
maximum bud diameter just before the expansion of the ray ﬂorets, while
parameters b and c affect the y-intercept and Slope, respectively. To incorporate
the temperature response, parameters a, b and c can be replaced by functions

of temperature fa( T), fb(T) and fc( 7'). Thus equation [4] becomes:

fa(T) [5]
: 1+ fb(T)efc(T)(tr-t)

 

B

To calibrate the bud development model, the parameters a, b and c in Eq.
[4] were estimated independently for each temperature treatment by ﬁtting Eq.
[4] to the data set with the nonlinear regression procedure (PROC NLIN) in SAS

(SAS Institute, 1990). Actual temperatures from average date of VB to average

31

date of FLW were used for each treatment.

Parameter a was found to vary randomly across the temperature
treatments, and for the sake of Simplicity, was treated as a constant in this
model. Functions f,,(7) and fc(T) were formulated based on the trends in the
values of b and c values across the range of temperatures (Figure 1). The
resultant equation was then ﬁt simultaneously to the entire calibration data set
using nonlinear regression to estimate the parameters in f,,(T) and fc(T) as well as
the parameter a as a constant across all temperatures. For the ﬁnal estimation,
actual average temperatures from t to t, for each measurement were used.

To determine the number of days to ﬂower (1‘, - t) at a given bud diameter

(B) and temperature (T), equation [5] (with a as a constant) can be algebraically

I?)
'” W)

fc(T) . (" ' ’)

manipulated to produce:

 

 

To validate the bud development model, Eq. [6] was used to predict days to
ﬂower from given bud diameters and actual temperatures from measurement to
ﬂower for the second-year data. These were then compared with the observed
days to ﬂower for these measurements and temperatures by ﬁtting a line to the
predicted data vs. the observed data.

Other data relating to plant quality such as height, number and Size of
ﬂowers were analyzed using the general linear models procedure In SAS to

determine signiﬁcance of the main temperature effect and any trends. Data from

32

the two years were analyzed separately.

Bﬁﬂlﬁ

Rate of progress model. Rate of progress from force to FLW and from VB
to FLW increased linearly as temperature increased. Time from force to VB
increased from 17 to 23°C and leveled off at temperatures 223°C (Figure 2).
Taking this into account, the linear regression for force to VB was ﬁt only to data
points from temperatures 523°C.

In the validation experiment, where actual average times to a given event
were compared with times predicted from the ﬁrst year model, the average
deviation in time from force to VB was 4.0 days with a maximum deviation of 6.4
days at 20.5 °C. The average deviation for VB to FLW was 0.9 days with a
maximum deviation of 1.9 days at 29.3 °C and the average deviation for force to
FLW was 4.9 with a maximum deviation of 7.1 days at 19.9 °C.

Bud development model calibration. The rate of expansion of buds
increased with temperature from 17 to 29°C; parameters b and 0 increased
similariy (Figure 1). An exponential function was ﬁt to the estimated b values,
and a linear function was ﬁt to the estimated 0 values. These functions fb(T) and

fc(T) were then incorporated into Eq. [5] resulting in the following equation:

a [7]

- 1+ (1)16sz )e(01+02T)(lr-l)

 

where a, b1, b2, c,, and 02 are constants. When Eq. [7] was ﬁt to the entire data
set, the resulting model (Table 5) closely ﬁt the observed bud diameters for the

33

calibration experiment (R2 = 0.945)(Figure 3). When predicted days to ﬂower
using Eq. [6] were compared to actual days to ﬂower, data highly correlated (R2
= 0.89) (Figure 4, a-e).

Bud development model validation. When predicted time to ﬂower in the
second year was compared with actual time to ﬂower, there was a consistent
bias in both the slope and the intercept such that the model was most accurate
at the middle temperatures, ranging from 20-26°C (Figure 5). Largest deviation
was seen in the model at the 17°C treatment, very close to time of ﬂowering
(Figure 4, H).

Other plant qualities. There was no significant effect of temperature on the
number of ﬂowers the ﬁrst year, but the number of ﬂowers per plant decreased
markedly as temperature increased the second year. This decrease in ﬂower
number with increased temperatures was due to the signiﬁcant trend in the
number of ﬂowers per stalk, as there was no effect on the number of stalks per
plant (Table 6). Heights were lower on the average in the second year, but in
both years the lowest average plant height was achieved at 23°C. Diameter of
open ﬂowers decreased Signiﬁcantly from 47mm to 25mm as temperatures
increased from 17 to 29°C (Figure 6). The number of nodes formed from the
start of forcing to ﬂower initiation was not affected by temperature, and was very

similar for both years, averaging about 8 nodes.

34

Discussion

In the sub-optimum temperature range, rate of progress toward a given
developmental event can be described by a linear function. The ﬁrst year data
on which the time to ﬂower model was based clearly ﬁt a linear pattern for days
to FLW and days from VB to FLW, but for days to VB, the pattern was linear only
at temperatures 523 °C. For days to FLW and days from VB to FLW the
optimum must be at least 29 °C. For time to VB, the rate of development started
to level off as temperatures increased, which indicates that perhaps 29 °C is
near the optimum for this species.

Overall, times to VB and FLW were lower in the second year than in the
ﬁrst. This may have been due to several factors which were different in the
second year experiment, namely the long day treatment by day extension with
high-pressure sodium lights vs. night interruption with incandescent lights the
ﬁrst year, and the addition of VPD control in the second year. Faust and Heins
(1997) found that high pressure sodium lights (HPS) can Signiﬁcantly increase
the temperature of the shoot tip, reducing time to ﬂower. The additional radiation
from the day-extension treatment in the second year may have heated the
meristem sufﬁciently to have accelerated ﬂowering. The VPD control instituted in
the second year may also have reduced the cooling effects of transpiration,
resulting in warmer plants and faster ﬂowering.

The time from VB to FLW was practically unchanged from the ﬁrst to the
second year, which indicates that differences in time to FLW the second year

were due almost entirely to effects on time to VB.

35

Coreopsis verticillata ‘Moonbeam’ bud development was sigmoid which
contrasts with bud-development models on other species. Increase in diameter
of buds of Hibiscus moscheutos. another commonly grown herbaceous
perennial, was found to follow an exponential curve (Wang 1998), as did
increase in length of Easter lily buds (Fisher et. al., 1996).

Although C. verticillata ‘Moonbeam’ could be ﬂowered sooner at higher
temperatures, ﬂower number and ﬂower diameter decreased as temperatures
increased. This reduction in ﬂower size with increasing temperature concurs
with similar research results for other plants such as petunias (Shvarts et. al.,
1997), pansies (Pearson et. al., 1995) Impatiens (Lee et. al., 1990) and
Chrysanthemum (Karlsson, 1998). Pearson et al. suggest that the smaller ﬂower
size at higher temperatures may be due to a reduction in the duration of bud
development.

It was observed that stem strength was weaker at higher temperatures,
probably due to a reduction in stem diameter, although no data were taken to
substantiate this Observation. Similar results for tweedia (Oxypetalum
caenrleum) showed that stem diameter decreased linearly with increasing
temperature from 14 to 30°C (Arrnitage, 1990).

The models developed in the current study may be used by growers to
schedule ﬂowering of plants grown at different temperatures, estimate time to
ﬂower at a given bud diameter, or to adjust temperature settings to achieve
ﬂowering of C. verticillata ‘Moonbeam’ on a given date for commercial production

(Table 7). While higher temperatures caused faster blooming, ﬂower Size and

36

number was reduced. Thus the advantages of a reduction in time to ﬂower must

be weighed against a corresponding reduction in plant quality.

37

Literature Cited

Armitage, AM. 1989. Herbaceous perennial plants; Atreatise on their
identiﬁcation, culture, and garden attributes. Varsity Press, Athens, GA.

Armitage, A.M., N.G. Seager, l.J. Warrington D.H. Greer and J. Reyngoud.
Response of Oxypetalum caeruleum to irradiance, temperature and
photoperiod. 1990. J. Amer. Soc. Hort. Sci. 115(6):910-914.

Brondum, J.J. and RD. Heins. 1993. Modeling temperature and photoperiod
effects on growth and development of dahlia. J. Am. Soc. Hort. Sci.
1 18(1):36-42.

Criley, RA 1995. Temperature inﬂuences ﬂowering of Palakana (Telosma
cordata Merrill) under long days. HortScience 30(3):482-483.

Faust, J.E. and RD. Heins. 1993. Modeling leaf development of the African
violet (Saintpaulia ionantha Wend.). J. Amer. Soc. Hort. Sci. 118(6):747-
751)

Faust, J.E. and RD. Heins. 1997. Quantifying the inﬂuence of high-pressure
sodium lighting on shoot-tip temperature. Acta Hort. 418285-91.

Fisher, P.R., J.H. Lieth and RD. Heins. 1996. Modeling ﬂower bud elongation
in Easter lily (Lilium Iongiﬂorum Thunb.) in response to temperature.
HortScience 31 (3):349-352.

Hamaker, CK. 1998. Inﬂuence of photoperiod and temperature on ﬂowering of
Asclepias tuberosa, Campanula carpatica, ‘Blue Clips’, Coreopsis
grandiﬂora ‘Early Sunrise’, Coreopsis verticillata ‘Moonbeam’, Lavandula
angustifolia ‘Munstead’, and Physostegia virginiana ‘Alba’. MS Thesis,
Dept. of Horticulture, Michigan State Univ., East Lansing.

Harrison, D. 1996. Colour is the key in selling perennials. Greenhouse Canada
Sept 1996, 32-33.

Karlsson, MG. 1992. Leaf unfolding rate in Begonia Xhiemalis. HortScience
27(2):109-110.

Karlsson, M.G., R.D. Heins and J.E. Erwin. 1988. Quantifying temperature-
controlled leaf unfolding rates in ‘Nellie White’ Easter lily. J. Amer. Soc.
Hort. Sci. 113(1):70-74.

38

Karlsson, M.G., R.D. Heins, J.E Erwin, R.D. Berghage, W.H. Carlson and J.A.
Biembaum. 1989. lrradiance and temperature effects on time of
development and ﬂower Size in Chrysanthemum. Scientia Hort. 39:257-
267.

Larsen, R.U. 1990. Plant growth modelling by light and temperature. Acta Hort.
272:235-242.

Lee, W., J.E. Barrett and TA. Nell. 1990. High temperature effects on the
growth and ﬂowering of Impatiens wallerana cultivars. Acta Hort.
272:121-127.

Nau,J. 1996. Ball perennial manual; Propagation and production. Ball
Publishing, Batavia, IL.

NeSmith, OS. 1997. Summer squash (Cucurbita pepo L.) Leaf number as
inﬂuenced by thermal time. Scientia Hort. 68(1997) 219-225.

Pearson, S., P. Headley, and A.E. Wheldon. 1993. A reanalysis of the effects of
temperature and irradience on time to ﬂowering in Chrysanthemum
(Dendranthema grandiﬁora). J. Hort. Sci. 68:89-97.

Pearson, S., A. Parker, S.R. Adams, P. Hadley and DR. May. 1995. The
effects of temperature on the ﬂower size of pansy (Viola xwittrockiana
Gams.) J. Amer. Soc. Hort. Sci. 70(2)183-190).

Roberts, E.H. and R.J. Summerﬁeld. 1987. Measurement and prediction of
ﬂowering in annual crops, pp.17-50. In: J.G. Atherton (ed.). Manipulation
of ﬂowering. Butterworths, London.

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Whitman, C.M., R.D. Heins, A.C. Cameron and W.H. Carlson. 1997. Cold
treatment and forcing temperature inﬂuence ﬂowering of Campanula
carpalica ‘Blue Clips”. HortScience 32(5):861-865.

Wang, 8., RD. Heins, W.H. Carlson and AC. Cameron. 1998. Modeling the

effect of temperature on ﬂowering of Hibiscus moscheutos. Acta Hort.
456:161-169.

39

Yuan, M., W.H. Carlson, R.D. Heins and AC. Cameron. 1998. Effect of forcing
temperature on time to ﬂower of Coreopsis grandiﬂora, Gaillardia

xgrandiﬂora, Leucanthemum xsuperbum and Rudbeckia fulgida.
HortScience 33(4):663-667.

40

Table 4. List of abbreviations and parameters.

 

 

DTE
FLW

VB
VPD

Parameter in bud development model

Flower bud diameter

Parameter in bud development model
Parameter in fb(T)

Parameter in fb(T)

Parameter in bud development model
Parameter in fc(T)

Parameter in fc(T)

Cumulative thermal time

Days to event

Flower (expansion of ray ﬂorets)
Parameter in linear timing model (intercept)
Parameter in linear timing model (slope)
Time of bud measurement

Time of ﬂower

Average air temperature

Base temperature

Visible bud

Vapor pressure deﬁcit

mm
dimensionless
dimensionless
001

days‘1

days‘1

°C'1 . days‘1
°C . days
days

event . days‘1
event . °C'1 . days1
days
days
°C
°C

 

41

Table 5. Nonlinear regression results from ﬁtting Eq. [4] to the full calibration
data set using actual temperature data for each measurement. The number of
observations in the data set was 421, and the R2 was .945.

   

conﬁdence interval

 

Parameter Estimate Asymptotic Lower Upper

 

b1 0.00897 0.00481 -0.00051 1 0.0184
b2 0.0854 0.0147 0.0563 0.114
61 0.0283 0.0159 -0.00298 0.0596
02 0.00550 0.000678 0.00417 0.00684

 

Table 6. Signiﬁcance of effect of temperature on height at ﬂower, number of
nodes added in forcing, ﬂower diameter, number of visible buds at ﬁrst ﬂower,
number of stalks, and number of visible buds per stalk at ﬁrst ﬂower for
Coreopsis verticillata ‘Moonbeam’.

 

 

 

     

 

 

 

 

 

main temperature trends
. . effect . .
“lama"; - _- _, ___ _ __ear . _ ._ "near -_ Wdat'
height at ﬁrst ﬂower 1 *** *** ***
NS

2 *** ~ ***
NS NS NS

number of nodes added 1
NS NS NS

2
ﬂower diameter 2 *** *** ***
. . NS NS NS

total number of VlSlbIe 1
bUdS at ﬁrst ﬂower 2 *** *** *
number of stalks 2 NS NS NS
number of visible buds per 2 *** *** **

stalk at ﬁrst ﬂower

 

”S, *, **, *** Non signiﬁcant or signiﬁcant at P5 0.05, 0.01, or 0.001 respectively

42

Table 7. Relationship between bud diameter, temperature, and time to ﬂower for
Coreopsis verticillata ‘Moonbeam’ according to Eq. 6.

 

 

 

 

 

 

. Bud F F F f Nu—burof days to ﬂower at indicaetd emptr in °C: _
draggger 17 18 19 20 21 22 23 24 25 26 27 28 29
1 39 39 38 37 37 36 35 35 34 33 32 32 31
1 .5 35 34 34 33 32 32 31 30 30 29 28 27 27
2 32 31 30 30 29 28 28 27 26 25 25 24 23
2.5 29 28 27 27 26 25 25 24 23 22 22 21 20
3 26 25 24 24 23 22 22 21 20 20 19 18 17

3.5 23 22 22 21 20 19 19 18 17 17 16 15 15
4 20 19 18 18 17 16 16 15 14 13 13 12 11
4.5 16 15 14 14 13 12 12 11 10 10 9 8 7
5 11 10 9 8 8 7 6 6 5 4 4 3 2

 

43

 

.
_x
(I!

0.10 -

Parameter value

0.05 ~

 

 

 

0.00 . T . ; .
17 20 23 26 29
Temperature (°C)
Figure 1. Parameters as ﬁt to each temperature treatment individually, and the
lines ﬁt to them using Eq. [7] ﬁt to the whole data set. Parameter b is indicated

by closed circles and exponential function shown as a solid line, while parameter
c is indicated by open circles and straight dashed line.

 

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' (a) 17°C
' (17.3)

    
  
 

 

(b) 20°C
(19.7)

 

 

 

 

E - (c) 23°C
g (23.5)
e
0.)
E
.9
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(d) 26°C
(26.1)
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(e) 29°C
(29.3)

 

 

 

O-‘NOO-bU'lO'JO—‘Nw-hmmo-INOOAU'IODOANQAU‘IO‘JO-‘NWAUICD

 

0 1 0 20 30 40
Days to ﬂower
Figure 3. Observed bud diameters at various times before ﬂower for each temp-

erature treatment from the calibration data set for C. verticillata 'Moonbeam'.
Line indicates bud diameter as modeled according to Eq. [7]. R2 = .945.

46

 

 

. j
. .. .

Le) 1,770 (17.3) i i ‘ __(fli1T9ll7-7l A _ ‘ . _ ._

   
 

l 1 l

 

-20 _.,....'l l . J. —'l l J

 

 

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__(hI23'C (23.-0.)... l ' '
L. .. 3.. ‘

 

 

         
 

QO_JW;W.¥JJM _jmyI.jlwIﬂm
Lid.) 2679(26-1) _ ,

 

 

Predicted days to ﬂower

  
    

 

l ; L -1. ‘I ;.
(1)293 (29.-4).. . . 245'. . .

' l I I
30 Llel2979129-3) , ,-

 

 

)—

      
 

 

 

 

 

l I d I i‘L'I .' lld
0 10 20 30 40 0 10 20 30 40
1st year observed days to FL 2nd year observed days to FL

 

 

Figure 4. Predicted days to ﬂower for C. verticillata 'Moonbeam' from a given
budediameter based on Eq. [6] vs. observed days to ﬂower from a given bud
diameter from the validation data set. Black line shows regression ﬁtted to data
points. Gray line represents 1:1 relationship.

47

 

1.2..
1.1,»

 

1.0

 

0.9.. .1.
0.8» .1
o_7.._..,..i_

Slope (open circles)

0.6+M
o.5~..b

 

0.4 # . .

 

 

' I i . ‘. '
T r l

 

 

17 20

23 26 29

Temperature (°C)

Figure 5. Slope and intercept of regression lines ﬁt to predicted vs. observed
second year data. Actual average temperatures from average date of visible
bud to average date of ﬂower were used. Slope is indicated by open circles and
corresponds to the axis on the left, while intercept is indicated by closed circles

and corresponds to the axis on the right. The gray line indicates where slope

and intercept would be for a 1:1 line.

48

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t a;
E 20 E
3
Z
0 o

 

16 18 2O 22 24 26 28 30 16 18 20 22 24 26 28 30
Temperature (°C) Temperature (°C)

Figure 6. Inﬂuence of forcing temperature on plant height, number of nodes
formed during forcing, diameter of open ﬂowers, number of ﬂowers, number of
stalks per plant, and number of ﬂowers per stalk for Coreopsis verticillata
'Moonbeam'. Filled circles represent ﬁrst year data, open circles represent
second year data. Error bars show standard deviation.

49

THE RESPONSE OF LONG-DAY HERBACEOUS PERENNIALS TO

A NIGHT-INTERRUPTION AT LOW NIGHT TEMPERATURES

50

Abstract

The effectiveness of a four-hour night interruption (NI) to induce ﬂowering
in the long-day herbaceous perennials, Achillea L. ‘Anthea’, Campanula
carpatica Jacq. ‘White Clips’, Coreopsis grandiﬂora Hogg ex Sweet ‘Early
Sunrise’, C. grandiﬂora ‘Sunray’, C. verticillata L. ‘Moonbeam’, Oenothera
missouriensis Sims, 0. speciosa Nutt., and Rudbeckia fulgida Ait. ‘Goldsturrn’
was tested at six different night temperatures. Plants were grown under natural
short days (9:03 hrs to 11:35 hrs) December through March, augmented with a
four-hour NI from 2200 to 200 hours provided by 60-W incandescent lights at 3
to 5 umol rn‘2 3". Night temperature setpoints were 2.5, 5, 10, 15, 20, and 25 °C
with a clay temperature setpoint of 25 °C for all treatments (actual average
temperatures during the 4-h NI varied from 3.4 to 247°C).

Flower induction occurred in most species at all night temperatures.
Flowering percentage for O. missouriensis, O. speciosa and C. ‘Sunray’ varied
widely among treatments in the ﬁrst year. An increase in the number of nodes
developed prior to ﬂower induction and a lower ﬂowering percentage at
temperatures above 20° C indicated some heat delay in O. speciosa, A.
‘Anthea’, and in smaller, second-year material of C. ‘Early Sunrise’.

Night temperatures as low as 3.4° C did not inhibit ﬂowering of any
species. Therefore the species tested in this experiment perceived long days
delivered by a 4-h night-interruption at night temperatures from 3.4 to 24.7 °C

with day temperatures of ~25°C.

51

Introduction

A four-hour night interruption (NI) is an effective way to promote ﬂowering
in many long-day herbaceous perennials under natural short-day conditions
(Runkle et al., 1998). Some perennials are commercially grown outdoors in the
early spring and are, under normal temperature conditions, exposed to low night
temperatures. To accelerate ﬂower induction in early Spring when natural
photoperiods are too short, commercial growers often provide Nl lighting. Under
low-temperature conditions, Shillo and Halevy (1985) found that ﬂowering
percentage for Gypsophila paniculata ‘Bristol Fairy’ was severely reduced under
long days delivered by day lengthening (additional hours of light in both morning
and evening) when night temperatures were _<.17°C. Hicklenton et al. (1993),
obtained similar results with a 18-h day-extension lighting on the same cultivar.
It is not known whether other long-day herbaceous perennials might be affected
similariy when subjected to NI lighting at low night temperatures.

Our objective was to determine the effectiveness of NI long-day lighting
treatments in promoting ﬂowering of several long-day herbaceous perennials
when delivered at different night temperatures.

As the main interest was whether the plants would ﬂower, and if so,
whether there was any delay in initiation, data were taken as to whether the plant
differentiated a ﬂower bud or not, and at what node with respect to the start of

forcing.

52

Materials and Methods

1"" year. In early December 1996, ﬁve species of perennials were
received from commercial growers. Species studied, plug size and exact
numbers and dates regarding plant material are presented in Table 7. Plants
were transplanted into 13-cm square containers (1.1L) at the start of treatments
(unless otherwise noted in Table 7). Long days consisted of natural days (9:03
hrs to 11:35 hrs) December through March, plus a 4-hour night interruption from
2200 to 0200 hours at 3 to 5 pmol rn‘2 s‘1 as measured by a LI-COR quantum
sensor model Ll-189 (Ll-COR, Lincoln, Neb.) provided by 60-W incandescent
lights.

Day temperature (from 800-1800 HR) was set at 25°C for all treatments,
while night temperature (NT) was set at 25, 20, 15, 10, 5 or 25°C. On some
nights when prevailing outside temperatures were not low enough, it was not
possible to maintain the coolest night temperature set points. Actual average
daily temperatures for each treatment, and average temperatures during the NI
lighting period for each treatment presented in Table 8. Temperature in each
greenhouse was recorded continually with a CR-10 datalogger (Campbell
Scientiﬁc, Logan, Utah).

After 11 weeks of NI treatment, plants that had not reached visible bud
were dissected under a stereoscope to determine if ﬂower buds were present.
Data recorded were: number of nodes at the start of forcing, presence or
absence of a terminal ﬂower bud, and number of nodes developed from the start

of treatments to the ﬁrst ﬂower bud or inﬂorescence.

53

2nd year. The same procedures were followed the second year for six
perennial species, except that at the end of treatment (Feb 15 for NT treatments
10-25°C, or March 8 for 2.5-5°C treatments), plants which had not reached
visible bud were moved to natural short days at 20°C and held until
approximately March 31, 1998. As well, 400W high-pressure sodium lamps
were added to provide 50 umol m'2 s‘1 supplemental light. The lights were turned
on when photosynthetic photon ﬂux (ppf) levels in the greenhouse dropped
below 200 umol m'2 s“, and turned off when ppf exceeded 400 umol m'2 s". A
control group was also added, which was held at a constant 20°C set temp-
erature and natural short days for the duration of the experiment.

Flowering percentage and average number of nodes formed during
forcing were determined for each treatment. New-node data was tested for
signiﬁcant linear and quadratic trends using the general linear models procedure
(PROC GLM) in SAS (SAS Institute, 1990).

Results and Discussion

Percentage ﬂower initiation. Most plants of A. ‘Anthea’, C. verticillata, R.
fulgida, C. carpatica, and C. grandiﬂora ‘Early Sunrise’ initiated ﬂowers in all
treatments. All 0. missouriensis plants initiated ﬂowers the second year, while
only about 60% did so the ﬁrst year. In the ﬁrst year, 0. speciosa and C.
grandiﬂora ‘Sunray’ demonstrated an incomplete and variable pattern of initiation
over the temperature treatments. None of the plants in the control group in the
second year initiated ﬂowers. There was no evidence that night temperatures as

low as 3.4°C affected the ability of these eight herbaceous perennials to initiate

54

ﬂowers (Figures 6,7).

Nodes formed prior to initiation. The number of nodes formed prior to
ﬂower initiation from the start of long days indicates whether any treatment had
delayed ﬂower induction. With the exception of R. fulgida and C. grandiﬂora
‘Sunray’, the number of nodes formed prior to ﬂower initiation was either not
affected or was increased by increasing night temperature (ﬁgures 6, 7). Flower
initiation was strongly delayed in A. ‘Anthea’ and O. speciosa as night
temperature increased above 15°C (Figure 6).

In the second year C. grandiﬂora ‘Early Sunrise’ also showed an increase
in the number of nodes added during forcing above 15°C night temperatures, as
well as a Slight decrease in the percentage of plants ﬂowering, which would
indicate heat delay. This trend was not evident in the ﬁrst year, perhaps
because the plant material in the ﬁrst year was larger (ﬁrst year material
averaged ~16 nodes , while second year material averaged ~13 nodes). While
cold night temperatures did not cause any adverse effects on ﬂowering for this
species, night temperatures above approximately 15°C may delay initiation in
plants with 13 or fewer nodes (Figure 7).

For C. grandiﬂora ‘Sunray’ ﬂowering percentage varied widely across
treatments, and no treatment achieved 100% ﬂowering (Figure 7). Coreopsis
‘Sunray’ normally requires vemalization before long day treatment in order to
ﬂower, but short days may substitute for this cold requirement (Runkle, 1996). It
is possible that these plants did not receive enough Short days before the start of

treatments to ensure 100% ﬂowering.

55

On the other hand, 0. missouriensis, which also showed irregular
ﬂowering in the ﬁrst year, had 100% ﬂowering in all treatments in the second
year, which suggests that perhaps the addition of supplemental lighting may
have affected ﬂowering responses. Thus, it may have been low light levels (lack
of supplemental lighting) which was the cause of variable ﬂowering percentages
across treatments in C. grandiﬂora ‘Sunray’, O. missouriensis and O. speciosa in
the ﬁrst year.
the species tested, a low night temperature does contribute to an overall
lowering of average daily temperature (see Table 8), which slows developmental
rates in general (Roberts and Summerﬁeld, 1987; Wang, 1998; Yuan, 1998). On
the other hand, many of the species tested Showed evidence of heat delay as
night temperatures increased above approximately 15-20°C. As all treatments
experienced relatively high day temperatures of ~25°C. this delay may have
been due to high average daily temperature, or it may have been due speciﬁcally
to high night temperatures. While the species tested in this experiment
perceived long days delivered by a 4-h night-interruption at night temperatures
from 3.4 to 247°C, growers should take into account other possible effects of
night temperature on timing, such as heat delay or delay due to a low average

daily temperature.

56

Literature Cited

Hicklenton, P.R., S.M. Newman and L. J. Davies. 1993. Night temperature,

photosynthetic photon ﬂux, and long days affect Gypsophila paniculata
ﬂowering. HortScience 28(9):888-890.

Roberts, E.H. and R.J. Summerﬂeld. 1987. Measurement and prediction of

ﬂowering in annual crops, pp.17-50. In: J.G. Atherton (ed.). Manipulation
of ﬂowering. Buttenrvorths, London.

Runkle, ES. 1996. The effects of photoperiod and cold treatment on ﬂowering
of twenty-ﬁve species of herbaceous perennials. MS Thesis, Dept. of
Horticulture, Michigan State Univ., East Lansing.

Runkle E.S, R.D. Heins, A.C. Cameron, and W.H. Carlson. 1998. Flowering of

herbaceous perennials under various night interruption and cyclic lighting
treatments. HortScience 33(4):672-677.

SAS Institute. 1990. SAS/STAT users guide, release 6.12 ed. SAS lnst., Cary,
NC.

Shillo, R. and AH Halevy. 1982. Interaction of photoperiod and temperature in
ﬂowering-control of Gypsophila paniculata L. Scientia Hort. 16:385-393.

Wang, 8., RD. Heins, W.H. Carlson and AC. Cameron. 1998. Modeling the

effect of temperature on ﬂowering of Hibiscus moscheutos. Acta Hort.
456:161-169.

Yuan, M., W.H. Canson, R.D. Heins and AC. Cameron. 1998. Effect of forcing
temperature on time to ﬂower of Coreopsis grandiﬂora, Gaillardia

xgrandiﬂora, Leucanthemum xsuperbum and Rudbeckia fulgida.
HortScience 33(4):663-667.

57

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Table 8. Average daily temperatures and temperature during 4-h night
interruption (NI) for each treatment in the ﬁrst and second year.

 

 

 

 

 

Set temperature Year 1 temperatures Year 2 temperatures
day/night 0C mg daily NI ﬂ daily j NI

25/25 24.7 24.7 24.5 24.6
25/20 21.9 19.5 22.2 19.8
25/15 19.5 14.9 19.3 14.6
25/10 17.3 10.5 16.8 10.4
25/5 14.2 5.5 16.2 7.0
25/2.5 13.7 3.4 15.5 4.9

 

59

Nodes added during forcing

 

 

 

 

 

 

 

 

 

 

 

 

 

A—A—A—A—A—A -
30 _ . 100
25 - - 80
20 - - 60
15 - L 40
10 - . 20
Achillea -
3 - a) m... ”'Anthea' . . , '
A—o—A—A—H - 100
16 - °_ 80
12 ‘ M L °°
8 - l 40
4 - ... Coreopsis verticillata F 20
b) LNS O f) 'Moonbeam' °
0 . I i I . l L I . I . I . i . l . 4 I o
F 100
25 — \ / L
20 - ' 80
15 _ _- 60
5 _ ... Rudbeckia fulgida - 20
C) L Q 9) 'Goldsturm’ ~
0 . l . L . I . l . g . 14. L . I I . I O
— 100
30 . L so
20 - '_ 40
10 ‘ Oenothera L 20
d L... 0". h . _
0 E) I . I J I L J ) SP 69,018 8. i 2 I . I 0

 

0 5101520250 510152025
Night temperature (°C)

Figure 7. Graphs a-d Show average number of nodes added from the
start of treatments to the ﬁrst ﬂower bud. Error bars show 95% conﬁdence
interval. Graphs e-h show ﬂowering percentage. Closed circles represent
data taken the ﬁrst year, while open triangles represent data taken the
second year. Linear trend (L) or quadratic trend (Q) nonsigniﬁcant (”3),

Or signiﬁcant at P=0.05 (*), 0.01 (**), or 0.001 (***).

60

6uuemou aﬁetueored

Nodes added during forcing

 

 

 

 

 

 

 

 

 

 

 

 

 

— 100
‘ L
20 _ 80
16 ‘ ’ 60
12 - 7
8 - f 40
4 Oenothera - 20
0 . Ail-t. OI" . I I : I e.)ni1is.soqn;egins . I . I b O
- 100
25 - .
20 _ - 80
15 _ 1 60
10 _ - 40
5 - b o LNS 0*“ f Campanula carpatica F 20
O ) A1 L*:. Qt" . 1 I l ) 'VIVhitGIC'ipS: . l I l h 0
W " 100
20 - _ 80
15 - L 60
10 - ~ 40
5 ° 0 L“ 0* Coreopsis randiﬂora F 20
O C.) AIL”? 01*". I l l 9.) 'IEarly Isuinngise; l J 1 i O
- 100
12 — l 80
3 - F 60
— 40
4 . .
Coreo Sis randiﬂora - 20
d) L” ONS h) .Sunra’; 9 _
O . I . I . l 4 l 4 1 . l . I l . l . I O
0 5 1o 15 20 25 o 5 10 15 20 25
Night temperature (°C)

Figure 8. Graphs a-d show average number of nodes added from the

start of treatments to the ﬁrst ﬂower bud. Error bars show 95% conﬁdence
interval. Graphs e-h show ﬂowering percentage. Closed circles represent

data taken the ﬁrst year, while open triangles represent data taken the

second year. Linear trend (L) or quadratic trend (Q) nonsigniﬁcant(

Or signiﬁcant at P=0.05 (*), 0.01 (**), or 0.001 (***).

61

“3).

Buuamou aﬁetueored

APPENDIX A:

NEW SPECIES SCREEN

62

INTRODUCTION

As perennials have become more popular, the demand for growers to
produce them has increased. Since selling plants in bloom increases both their
value and desirability, recent research has focused on how to bring perennials
into ﬂower on demand. As a preliminary step in the research process, species
new to the MSU perennial program are put through a simple experiment
designed to elucidate the basics of their requirements to ﬂower.

To determine whether they require cold to ﬂower, they are given either 15
weeks of cold treatment at 5°C, or no cold treatment. These plants are then
divided into short day treatments (9-h) or long day treatments (9-h with a 4-h
night interruption) to ﬁnd out what photoperiod they require to bloom. In addition
to noting whether and when the plants ﬂower, measurements such as height and
number of ﬂowers are recorded. Informal observations are made as to the
potential of each species as a ﬂowering potted plant.

The new species screen provides an information base from which to
choose species which have promise for the grower based-on appearance and
ease of production. Those plants which show potential are then studied in more
detail. The data taken in the new species screen helps the researcher to know
what to expect from the plant, and to design experiments to pinpoint cold,

photoperiod and temperature responses.

63

PROTOCOL

OBJECTIVE: To screen various species for ﬂowering response under long and
short days and before and after cold treatment.
EXPERIMENTAL DESIGN:
Plant Material: See table 9
Photoperiods:

1) 9 hours (0800 - 1700)

2) Night interruption from 2200 to 0200 HR with incandescent lamps
Cold Treatments:

1) No cold treatment

2) 15 weeks at 5°C (9-h photoperiod from cool-white ﬂuorescent light)

Plant Requirements:
10 plants x 2 photoperiods x 2 cold treatments = 40 plants/species

RESEARCH PROTOCOL:

Half of the plants of each species will be planted into 5" square pots and
put under the indicated photoperiods upon arrival; the other half will be put into a
5°C cooler for 15 weeks and then potted up and put under photoperiod
treatments. Greenhouse forcing temperatures will be set at a constant 20°C.
Data collected will include:

1) Initial leaf count

2) Date of visible bud/inﬂorescence

3) Date of ﬂowering

4) Final leaf number at date of ﬂowering

5) Number of ﬂower buds/inﬂorescences at date of ﬂowering
6) Height of plant/inﬂorescence at date of ﬂowering

64

Table 9. New species screens 1997-1999. Production information, including
rating as a potted plant, cold and photoperiod recommendations, based on the
treatments given in this screen, and approximate weeks to ﬂower at 20°C.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

—--- _, —- -—-——----——~— === —— ————-—— ~ — — — -—
rating I

I as 15 rovide wks to I
I Species/Cultivar t weeks p NI? FL at Comments I
, 9° cold? 20°C I
. plant I

—‘ ." " ‘ "‘ ‘ ‘ —‘ ___—T“ __‘_‘ “ _ ***” ‘ ‘ ‘ ‘ ‘ " I

' Ichn’IIIIeGaa’ amt.» yes yes 7 Lots of long lasting ﬂowers I

~ Achillea ptannica very susceptible to powdery

. ‘The Pearl’ “I “9“ yes 5 mildew {

I Agastache very long bloom time

, ‘Pink Panther’ m1? rec. no 6 some PGR work needed .

1 Ajuga reptans nice with or without ﬂowers

I ‘Bronze Beauty’ 121312 yes no 3 and easy I

; Anemone hupehensrs {we yes yes 14 a nice show of pink ﬂowers I

|

' Anemone sylvestris ﬂ 9 9 2 Inconsistent ﬂowering and I

; ‘ ' short lived blooms I

L gzgzggsesgfha 12121:» yes yes 14 very similar to A. hupehensis

. I

' Aster alpinus i? es 7 5 nice ﬂowers, but ﬂowering I

I ‘Goliath’ y ' was inconsistent I

: . I

I Aster dumosrs 1112 yes no 8 needs work with PGRs ‘

, Purple Dome I

. Aubrieta easy. nice ﬂowers but

I ‘Whitewell Gem’ I“? yes no 3 scraggtly
Campanula good but not as nice
portenschlagiana m“? yes no 5 as ‘Birch Hybrid’

Clematis montana a nice show if you can
‘John Paul II’ “If" yes yes 12 contain it.

Flethra alnifolia ‘Rosea’ 1’32 yes “:25 15 inconsistent ﬂowering
Coreopsis auriculata it: if? no 7 4 short & cute, but needs
‘Nana’ ' photoperiod work

. like pink C. verticillata -
Coreopsrs rosea 12111? rec. yes 7 reat, but may need stakin
Dianthus deltoides few ﬂowers — also needs
‘Shrimp’ 6 yes "° 8 juvenility work

12131? = excellent, ready for pot culture rec. = recommended

ﬁrst: = consistent, not ready for pot culture prob. = probably

it = not suited for pot culture at this time

65

not neces. = not necessary
PGR’s = plant growth regulators

Table 9 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

Species/Cultivar Comments
,- I Pa_'"‘ ___I__ I _ _ , I-
, Dianthus deltoides 1k rob prob. _ no ﬂowers from plugs—
‘Canta Libre’ p ' not needs juvenility work
. Dicentra exrmia m: yes no 6 could be nice but needs
Luxunant cultural work
Echinacea purpurea needs work with PGRs or
‘Magnus’ 1m rec. yes 15 other height reduction
Geranium long bloomer — needs work
' ‘Johnson’s Blue' W rec' "° 6 with PGRs
Geum not needs work with PGRs
‘Mrs. Bradshaw’ {:32 yes neces. 8 otherwise v. nice
Gypsophila paniculata needs PGRs, as recom-
T ‘Happy Festival’ and? yes yes 11'5 mended by breeder :-
gelenrum mt» yes yes 10 needs work with PGRs
runo
- Helenium autumnale . I
. ‘Red & old Hybrid’ my yes yes 14 needs work With PGRs I
. , . , not yes if I
, Hemerocallis Rocket City 12121:: neces. no cold 15 needs a gallon pot
I Iris ﬂowers extrememly short-
7
I ‘Sambo’ {I ' yes 3 lived
I Lewisia cotyledon mi: rec. no 12 beautiful show, but
i mconsrstent ﬂowenn
I Lychnis coronan'a n, es 7 8 inconsistent ﬂowering -
; ‘Angel Blush’ y ' needs juvenility & PGR work
I .
Oenothera frutrcosa not .
l
I ’Youngii-Lapsley' 1212* yes neces. 6 a great display.
: Pennisetum alopecuroides 1’: 7 7 _ did not ﬂower under any
T ‘Little Bunny’ ' ' treatment
I Polygonum afﬁne
I ‘Dimity' 12???? yes yes 13 not very showy
1 Potentilla atrosanguinea 1’? es 7 7 inconsistent ﬂowering -
: ‘Miss Willmott’ y ' needs juvenility & PGR work
I Sidalcea 1: 1": not no 10 very nice but too tall — needs
I ‘Paiy Girls’ neces. work with PGRs

 

 

 

 

 

  

 

mm = excellent, ready for pot culture
serif: = consistent, not ready for pot culture
1!? = not suited for pot culture at this time

66

rec. = recommended

prob. = probably

not neces. = not necessary
PGR’s = plant growth regulators

Table 9 (cont’d)

 

 
   
    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

rating 15
Species/Cultivar a; weeks prﬁl‘gje Comments
9 cold? ' 20°C
plant
Stokesia Iaevis ,, .
‘Klaus Jellito’ trim yes no 11 ﬁlls out a 5 pot very nicely
. Tanacetum low ﬂowering % - needs
- ‘Robinson Dk Crimson’ 1? rec. yes 15 juvenility work
Thalictrum aqui/egifolium it“: yes ? 8 inconSIstent and Mt very
showy
. . not very easy to ﬂower. Long
Tiarella when'yi 122121} no neces. 4 lasting display .
Tricyrtis nirta it yes yes 16 sparse ﬂowering, long force 1
Miyazaki time
TroIIi'us Iedebourii nice ﬂowers, but long force
‘Golden Queen’ i“? rec. no >15 time - juvenility?
“Veronica Iongifolia 12121? yes not 9 ﬁlls out a 5 pct nicely — tall
: leicle (veg) neces. white spikes
. mrnia’longifolia it n, 1:» yes . Ho 7 HI ouwoa5 pot — smaller

rec. = recommended

prob. = probably

not neces. = not necessary
PGR’s = plant growth regulators

{dd} = excellent, ready for pot culture
em = consistent, not ready for pot culture
11? = not suited for pot culture at this time

67

 

Percent Flowering Plant Node Development
50

 

 

 

 

 

 

   

 

 

 

   

 

 

 

 

 

 

   

100%
40 , , ,
75% 30
so-/. 20
25% , 1°
0% 2.32.. 0 Weeks 5C 15 Weeks SC
SD LD SD LD SD LD
m 0 weeks SC -15 weeks SC - Inltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
so
so
40
20
0
LD SD LD
mowedks 5c -1Sweeks 5c moweeks 5c -1Sweeks 50
Number of lnflorescences Plant Height at Flower
e
5
4 E
9.
3 z
2 +3
I
1
0
SD LD
W 0 weeks SC - 15 weeks SC m 0 weeks SC -15 weeks SC

 

 

 

 

 

 

Figure 9. Effects of photoperiod and cold treatment on Achillea 'Anthea' as
indicated. Error bars show 95% conﬁdence intervals.

68

 

Percent Flowering Plant Node Development
100% 7

 

    

 

  
       

e
no

15 Week SC
SD LD

 

 

 

 

LD

m 0 weeks SC -15 weeks SC - Inltlal Nodes m Nodes at Flower

 

 

 

 

Days to Visible Bud

80

Days to Flower

 

 

60

 

40

 

20

 

 

 

 

 

 

 

so LD so LD
m 0 weeks SC -15 weeks SC m 0 weeks SC -15 weeks SC
Number of Flowers Plant Height at Flower
50

 

Height (cm)
8

_s
O

   

0
SD LD

m 0 weeks SC -15 weeks SC

 

 

 

LD
m 0 weeks SC -15 weeks SC

 

 

 

Figure 10. Effects of photoperiod and cold treatment on Achillea ptarmica
'The Pearl' as indicated. Error bars show 95% conﬁdence intervals.

69

 

Percent Flowering
100% —- W , ,, A.

 

  

75%
50%
25%

0%

LD
m 0 weeks SC -15 weeks SC

 

Plant Node Development

 

    

Oeeks
SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud
140
120
100

80
60
40
20

0

 

SD LD
m 0 weeks SC - 15 weeks 5C

Days to Flower

 

SD

m 0 weeks SC - 15 weeks SC

 

 

Number of Inﬂorescences

35
30
25
20
15
10

5

 

 

my 0 weeks SC -15 weeks SC

 

 

Plant Height at Flower

 

 

egg

Height (cm)
M u #
O O

_s
O

 

 

O

 

m 0 weeks SC -15 weeks SC

 

 

Figure 11. Effects of photoperiod and cold treatment on Agastache 'Pink
Panther' as indicated. Error bars show 95% conﬁdence intervals.

70

 

 

Percent Flowering
100% ,,,,,,,,, L. 7., ,

  

75%
50%
25% ,

0%

m0 weeks SC -15 weeks SC

 

 

Plant Node Development
10 ’

 

 

0 Weeks 5C 15 Weeks SC
LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud
80
60
40

20

 

0
SD LD
m 0 weeks so - 15 weeks 5c

 

Days to Flower
80 '-

 

 

 

 

 

 

 

 

 

SD LD

m 0 weeks SC - 15 weeks 5C

 

 

Number of Inﬂorescences
2.0

 

 

1.5

1.0

0.5

 

 

 

 

0.0

SD LD
m 0 weeks SC - 15 weeks SC

 

 

 

 

 

 

 

 

Plant Height at Flower
16

A12 -

E

:2 a

5’ 4 .. --

 

    

 

 

o ....
SD LD

m 0 weeks SC -15 weeks SC

 

Figure 12. Effects of photoperiod and cold treatment on Ajuga reptans 'Bronze
Beauty' as indicated. Error bars indicate 95% conﬁdence intervals.

 

 

 

Percent Flowering Plant Node Development
100%

 

 

3° ‘ *.-. ’ "
25 . . .
75% 20
50% 15
10
25% 5
0

   

 

 

0%

 

0 Weeks 5C 15 Weeks SC
SD
SD LD LD SD LD

m 0 weeks SC -15 weeks SC - Initlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud Days to Flower

150 150
125
100
75
50
25
0

 

 

 

 

SD LD SD LD

m 0 weeks SC - 15 weeks 5C In 0 weeks 5C - 15 weeks SC

 

 

Number of Flowers Plant Height at Flower
100 100

80 80

60

a:
O

40

Height (cm)
A
O

20

N
O

 

0

 

0

LD SD LD
moynek; 5c -15w99ks 5c Maweeks SC -15weeks SC

 

 

 

 

 

Figure 13. Effects of photoperiod and cold treatment on Anemone hupehensis
as indicated. Error bars show 95% conﬁdence intervals.

72

 

 

Percent Flowering Plant Node Development
100%

 

 

75%

50%

25%

 

 

 

 

 

0%

 

0 Weeks SC 15 Weeks 5C
D
SD LD 5 LD SD LD

m 0 weeks 5c -15 weeks 5c - Inltlal Nodes m Nodes at Flower

 

 

 

 

Days to Visible Bud Days to Flower

1 50
1 20
90

 

60
30

   

0
SD LD SD LD

m 0 weeks SC - 15 weeks SC m 0 weeks SC - 15 weeks SC

 

 

 

 

 

 

 

 

 

 

 

 

 

Number of Flowers Plant Height at Flower

4 25
3 A 20
515

2 ..
f. 10

O
1 z 5
0

LD D
m 0 weeks SC -15 weeks 5c M 0 weeks SC -15 weeks SC

 

 

 

 

 

Figure 14. Effects of photoperiod and cold treatment on Anemone sylvestris as
indicated. Error bars show 95% conﬁdence intervals.

73

 

 

Percent Flowering Plant Node Development

 

 

 

 

 

 

 

 

 

 

 

 

 

100% . ________________________ 2°
16 ————— -I ——————
75% ———————————— 12
50% . ———————————— a ____________
25% I ____________ 4 “ “ -‘
0% OWeeksSC 15WeeksSC
SD LD SD LD

SD LD
”OweeksSC -15weeksSC -lnltlelNodesmNodesstFlower

 

 

 

 

Days to Visible Bud Days to Flower

 

 

 

 

 

 

 

 

 

 

 

120 120
so ________________________ so ____________
so so ____________
30 30 ____________
o 0
SD LD

 

momekssc -15weeksSC moweekssc -15weeksSC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Number of Flowers Plant Height at Flower
30 40
25 A 30 I ____________ ___-
20 g
15 E 20 . ——————————— 4————

2

10 f 10 IL- ___________ __-_

S

0 0

so LD

 

 

 

 

 

SD
m0weeks50 -1SweeksSC mOweeksSC -15weeksSC

 

 

 

Figure 15. Effects of photoperiod and cold treatment on Anemone vitifolia
‘Robustissima‘ as indicated. Error bars show 95% conﬁdence intervals.

74

 

Percent Flowering Plant Node Development
100% 50 ,

 

 

 

75%

 

50%

25%

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0% 0 Weeks 5C 15 Weeks SC
SD LD SD LD
m 0 weeks SC -15 weeks SC - Inltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
80
60
40
20
D SD
m 0 weeks 5c - 15 weeks 5c M 0 weeks 5c - 15 weeks 5c
Number of F|owers Plant Height at Flower

 

 

 

 

 

 

Height (cm)

 

 

 

 

 

 

 

LD SD

SD
m 0 weeks 5c - 15 weeks 5c 5529 0 weeks SC -15 weeks 5C

 

 

 

 

 

 

Figure 16. Effects of photoperiod and cold treatment on Aster alpinus 'Goliath'
as indicated. Error bars show 95% conﬁdence intervals.

75

 

Percent Flowering
100% e ______________________

 

75%

 

 

 

 

SD LD
mOweeks 5C -15weeksSC

 

 

Plant Node Development

50
40
30
20
1 0

 

 

 

OWeeksSC

 

 

SD LD

 

 

15 Weeks SC
SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud

140
120 ————————————
100 ____________

 

___—___

 

 

80
60
40 I. ——————
20
0

 

 

SD

 

140
120
100

Days to Flower

 

i.————-——-—-—-————i

_—___——-—e—_—-1

 

     

 

SD

—-—. _———_————q

 

LD

ll“I“Oweeks SC -15weeksSC

 

WOweeksSC -15weeks5C

 

 

 

Number of Flowers

 

 

SD

mamksSC -15weeks5C

 

 

 

LD

 

 

 

 

Plant Height at Flower

175

 

150
A125 .
3 100 <
75 <
50 .
25

m

Height

q————————————

u————_———————

——————_-_——ﬁ

 

__2p ________

 

 

 

LD

MOweeksSC -15weeks 5C

 

 

Figure 17. Effects of photoperiod and cold treatment on Aster dumosus as
indicated. Error bars show 95% conﬁdence intervals.

 

Percent Flowering

1 00%

75%

50%

25%

 

0%
SD LD

m 0 weeks SC -15 weeks 5C

 

 

Days to Visible Bud
30
25
20
15
10

 

0

SD LD
m 0 weeks 5C -15 weeks 5C

 

 

Number of Flowers

 

 

LD
m 0 weeks 5C - 15 weeks 5C

 

 

 

Plant Node Development
40

 

0 Weeks SC
SD LD

- Inltlal Nodes m Nodes at Flower

15 Weeks SC
SD LD

 

 

Days to Flower

 

SD LD

m 0 weeks 5C - 15 weeks SC

 

 

 

Plant Height at Flower

Height (cm)
A

N

 

SD LD
m 0 weeks 5C - 15 weeks SC

 

 

Figure 18. Effects of photoperiod and cold treatment on Aubrieta ’Whitewell
Gem' as indicated. Error bars show 95% conﬁdence intervals.

77

 

Percent Flowering

1 00%

75%

25%

 

0%
SD LD

m 0 weeks so -15 weeks 5c

 

Plant Node Development
25

20

    

15 Weeks
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud
140
120
100
80
60
40
20

0

 

m 0 weeks so - 15 weeks 5c

 

 

Days to Flower

140
120
100
80

60

40

20

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

Number of Flowers
400

300
200

100

 

SD LD
m 0 weeks SC - 15 weeks SC

 

 

Height (cm)

 

 

 

Plant Height at Flower

 

     

 

SD LD
m 0 weeks SC - 15 weeks SC

 

 

Figure 19. Effects of photoperiod and cold treatment on Campanula
portensch/agiana as indicated. Error bars show 95% conﬁdence intervals.

 

100%

75%

50%

25%

0%

 

Percent Flowering

 

———_—-——————i

_--—————————r

i————————_——e—i

 

 

 

SD

LD
mOweeksSC -15weeks5C

    

__——-J

__——‘

___—.4

 

 

 

 

Plant Node Development

40

 

301

20

10

 

 

 

SD LD

 

SD

 

 

9..
DO.
.0.

15 Weeks

LD

- Inltlal Nodes in: Nodes at Flower

 

 

120

30

 

Days to Visible Bud

 

 

 

 

 

 

“OweeksSC -15weeks50

 

 

 

 

120

30

Days to Flower

 

4i—————.———e—e—-——i

___-__—_——-—1

 

 

 

SD

    

.0.
I...

0..
D...

Ago

————-I

 

m0weeksSC -15weeks5C

 

 

14
12
10

 

Number of Flowers

 

 

 

 

 

 

m0weeks5c -15weeks5C

 

 

 

 

Plant Height at Flower

:5

uh
OO

0

Height (cm)
no a
O

 

 

 

 

 

 

“OweeksSC -15weeksSC

 

Figure 20. Effects of photoperiod and cold treatment on Clematis montana ‘John

Paul II' as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

 

 

Percent Flowering

1 00%

75%

25%

 

0%
SD LD

m 0 weeks SC -15 weeks SC

 

Plant Node Development

 

 

0 Weeks 5C 15 Weeks 5C
LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud

1 20
90
60
30

0

SD

R 0 weeks 5C -15 weeks SC

 

 

Days to Flower

 

SD LD

m 0 weeks SC -15 weeks SC

 

 

Number of lnflorescences
8

6

4

 

LD
m 0 weeks SC - 15 weeks SC

 

 

 

 

Plant Height at Flower

160
120

80

Height (cm)

40

 

0

SD LD
m 0 weeks SC -15 weeks SC

 

 

Figure 21. Effects of photoperiod and cold treatment on Clethra alnifolia ‘Rosea'
as indicated. Error bars show 95% conﬁdence intervals.

 

 

Percent Flowering

 

1 00%

  

75%

50%~

25%

0%

SD LD
m 0 weeks so -15 weeks 5c

Plant Node Development

 

 

 

 

 

 

 

0 Weeks SC 15 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud

 

60

 

40

 

20

 

 

 

 

SD
m 0 weeks SC -15 weeks 5C

 

Days to Flower

 

 

 

 

 

 

 

so

m 0 weeks SC -15 weeks SC

 

 

 

Number of Flowers

 

 

SD LD
m 0 weeks SC - 1 5 weeks SC

 

 

 

 

Plant Height at Flower

Height (cm)

 

LD
m 0 weeks SC -15 weeks SC

 

 

Figure 22. Effects of photoperiod and cold treatment on Coreopsis auriculata
'Nana' as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

Percent Flowering

100%

75%

50%

25%

 

SD LD

m 0 weeks sc -15 weeks 5c

 

Plant Node Development

 

 

0 Weeks 5C 15 Weeks SC
SD LD SD LD

- Initial Nodes m Nodes at Flower

 

 

 

Days to Visible Bud
60
50
40
30
20
10

0

 

SD LD
m 0 weeks so - 15 weeks 5c

 

Days to Flower

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

 

Number of Flowers

 

 

SD LD
m 0 weeks SC -15 weeks SC

 

 

 

Plant Height at Flower

40

u
0

N
0

Height (cm)

—L
O

 

SD
5883 0 weeks SC -15 weeks 5C

 

 

Figure 23. Effects of photoperiod and cold treatment on Coreopsis rosea as
indicated. Error bars show 95% conﬁdence intervals.

 

 

 

Percent Flowering

1 00%

75%

25%

 

0%

SD LD
m 0 weeks 5c -15 weeks 5c

Plant Node Development

    

0 Weeks 5C 15 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

 

Days to Visible Bud
60

50
40
30
20
1 0

0

 

SD LD

m 0 weeks 5c - 15 weeks so

Days to Flower

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

 

Number of Flowers

 

LD

S
m 0 weeks SC - 15 weeks SC

 

 

 

Plant Height at Flower

Height (cm)

 

SD
m 0 weeks 5C -15 weeks 5C

 

Figure 24. Effects of photoperiod and cold treatment on Dianthus deltoides
’Shrimp' as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

Percent Flowering

 

100% 10
3 ,,,,,, M
75% 6 ggggg j
50% 4 p _ _
25% 2I”””
0% 0 0 Weeks 1heeksSC
SD LD SD LD SD LD

m 0 weeks 5c -15 weeks 5c

 

 

Days to Visible Bud
220
200

60
40
20

0

 

SD LD
m 0 weeks 5C -15 weeks SC

 

 

 

 

 

Plant Node Development

 

 

      

 

 

 

 

 

- Initial Nodes m Nodes at Flower

 

 

Days to Flower

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

 

 

 

 

Number of Flowers Plant Height at Flower
50 30
40 25
30 E 20
E 15
2° L210 .
10 I 5
o 0

SD LD
m 0 weeks SC - 15 weeks SC

 

 

 

 

 

LB
6383 0 weeks SC -15 weeks SC

 

 

Figure 25. Effects of photoperiod and cold treatment on Dicentra eximia
'Luxuriant' as indicated. Error bars show 95% conﬁdence intervals.

84

 

Percent Flowering Plant Node Development

 

 

100% 35
30 eeeeeeeeeeeeeeeeee
15% 25 ***********
20
500/. 15

10
25%

       

 

 

 

0% 0 Weeks 5C 15 Weeks SC

SD SD LD
so LD L”
m 0 weeks 5C -15 weeks 5C - Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud

160

Days to Flower

120

80

40

 

0

 

SD LD

a 0 weeks SC - 15 weeks 5C m 0 weeks SC - 15 weeks SC

 

 

Number of Flowers Plant Height at Flower
12 100
80
60

40

Height (cm)

20

   

03.1th

SD LD
m 0 weeks 5C - 15 weeks SC

 

LD
m 0 weeks 5C - 15 weeks SC

 

 

 

 

Figure 26. Effects of photoperiod and cold treatment on Echinacea purpurea
'Magnus' as indicated. Error bars show 95% conﬁdence intervals.

85

 

 

Percent Flowering Plant Node Development

 

 

 

 

1oo% . ._ . 35
30

75% 25
20

50% 15

10

25% eeeee 5 ,, .7

    

 

 

 

 

 

 

 

 

0%

 

. z 0 Weeks SC 15 Weeks SC
SD LD
LD

 

 

 

 

LD
m 0 weeks SC -15 weeks 5C - Inltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
200

160

     

 

 

 

 

120
80
40
0
LD so
mOweeks SC -1Sweeks SC m0weeks SC -1Sweeks SC
Number of Flowers Plant Height at Flower

 

 

8

U
0

 

Height (cm)
N
O

_s
O

 

 

 

 

 

 

SD LD
EOweeks SC -1Sweeks SC mOweeks SC -15weeks SC

 

 

 

Figure 27. Effects of photoperiod and cold treatment on Geranium 'Johnson's
Blue' as indicated. Error bars show 95% conﬁdence intervals.

86

 

 

Percent Flowering

1 00%
75%
50%
25%

0%
SD LD

m 0 weeks 5c -15 weeks so

 

 

 

 

Plant Node Development
14

 

 

 

 

    

0 Weeks 5C 15 Weeks SC
SD LD SD LD

 

- Inltlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud

80
60
40
20
0

SD LD

m 0 weeks SC - 15 weeks 5C

 

 

Days to Flower

SD LD

m 0 weeks SC - 15 weeks 5C

 

 

 

Number of Flowers

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

 

Plant Height at Flower

50

Height (cm)
N U #
O O O

_L
O

 

0

 

m 0 weeks SC -15 weeks SC

 

 

 

Figure 28. Effects of photoperiod and cold treatment on Geum 'Mrs. Bradshaw'
as indicated. Error bars show 95% conﬁdence intervals.

 

Percent Flowering

 

 

   

 

Plant Node Development

 

 

 

 

80
60
40
20

SD

m 0 weeks sc - 15 weeks 5C

100% _, _ , eeeeee 5°
40
75% 30
500/. ..-, 20
25% e ,, , 1° ’
0% .:.:.;. 0 Weeks 5C 15 Weeks SC
SD LD SD LD SD LD
m 0 weeks 5C -15 weeks 5C - Inltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
120
100

 

SD LD

m 0 weeks SC - 15 weeks 5C

 

 

Number of Flowers

 

LD

m 0 weeks 5C -15 weeks SC

 

 

Plant Height at Flower

15
12

 

Height (cm)
O o) O to

SD LD
m 0 weeks SC -15 weeks SC

 

 

 

Figure 29. Effects of photoperiod and cold treatment on Gypsophila paniculata
'Happy Festival' as indicated. Error bars show 95% conﬁdence intervals.

88

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Percent Flowering Plant Node Development
100% I ........... ___- ___- 7°
60
75% F ——————————— I- ::;:; ————-+ 50
25252 40
50% ____________ _ _____ so
20 I
25% ___________ s- ..... 10
0% , m .;.;.;. 0 Weeks 5C 15 Weeks 5C
SD SD LD
so L0 L”
m 0 weeks 5C -15 weeks SC - Inltlal Nodes mNodes at Flower
Days to Visible Bud Days to Flower
140 140
120 120 ———————————————————————
100 100 _______________________
80 80 ____________ _
60 60 I ———————————— — _____
‘0 313133 ‘0 ”—— "-*- -----
2o zo -----
0 . :§:?:?:' 0 , 21:32:: 23:3:3:
SD LD

 

 

 

SD
mOweekssc -15weeksSC

 

 

LD

 

 

 

 

 

 

   

  

 

 

“OweeksSC -15weeksSC

 

 

 

 

Number of Flowers Plant Height at Flower

40 so

so ______________________ A so .
e
e

20 ———————————— -— ————— E 40 <
2

1o ____________ _ _____ :3 20 .

0 .__.__ 32:3:
LD

 

 

 

 

 

SD

   

 

 

 

 

 

 

 

 

mamkgsc -15weeks5C “OweeksSC -1SweeksSC

 

 

 

 

 

Figure 30. Effects of photoperiod and cold treatment on Helenium ‘ano‘ as
indicated. Error bars show 95% conﬁdence intervals.

89

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

percent Flowering Plant Node Development
100% I ——————————— ———— ————— 5°
4° ------------
75% . ———————————— — ————— 30 :5:-
5096 ———————————— — ————— 20
25% ____________ _ _____ 10 I
o I
0% 15 Weeks 5c
SD LD SD LD SD LD
m 0 weeks 5c -15 weeks so - Inltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
120 120
so ———————————————————————— so __________________
so ———————————— _ ————— 60 ____________ I— ___—4
so I ____________ _ _____ so ____________ _ _____
o » 0
SD LD SD LD
moweekssc -1SweeksSC moweeks5c -1SweeksSC
Number of Flowers Plant Height at Flower
so so
so . _______________________ . so . ____________ ___- -—-—-I
E
0
4o ———————————— ___- ————— E 40 ———————————— — ___-
.9
20 ____________ ---- _____ :2 20 ____________ _ ----
o , 0
SD LD SD LD
mOweeksSC -1SweeksSC m0weeksSC -15weeksSC

 

 

 

 

 

 

Figure 31. Effects of photoperiod and cold treatment on Helenium 'Red and
Gold Hybrid' as indicated. Error bars show 95% confidence intervals.

90

 

Percent Flowering

 

100%

75% ,

50% eeeee

25% .......

 

0%.

SD LD
m 0 weeks 5c -15 weeks 5c

  
   

Plant Node Development
20

 

15 ”We“;
10 ewe“ e

5 77-74,- ,

 

 

 

0 Weeks 5C 15 Weeks SC
SD LD SD L

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud

1 80
1 50
1 20
90
60
30
0

SD
m 0 weeks so - 15 weeks 5c

 

Days to Flower

SD LD

m0weeks 50 -15 weeks 50

 

 

Number of Flowers

 

SD LD
m 0 weeks 5C - 15 weeks 5C

 

 

Plant Height at Flower

80

 

A
O

Helght (cm)

N
O

   

 

 

mo weeks SC -15 weeks SC

 

 

Figure 32. Effects of photoperiod and cold treatment on Hemerocallis 'Rocket
City' as indicated. Error bars show 95% conﬁdence intervals.

91

 

Percent Flowering

100%

75%

50%

25%

 

0%

SD LD
m 0 weeks 5C -15weeks SC

 

 

Plant Node Development

 

      

 

 

 

12 7
1O kkkkkk “”7 g
3 ,,,,,,,,,,
6 — ——747
4 ,,,,,, _
2 e __,_,
0 :o:-:- 'ozozo: -:-:-:
0 Weeks 5C 15 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud

40
30
20

10

 

0
SD LD

m 0 weeks sc - 15 weeks 5c

 

Days to Flower

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

 

Number of Flowers

M13“)!

 

 

LD
m 0 weeks SC - 15 weeks 5C

 

 

 

Height (cm)

Plant Height at Flowe

16 ,

 

  

SD LD
m 0 weeks SC -15weeks SC

 

 

Figure 33. Effects of photoperiod and cold treatment on Iris 'Sambo' as
indicated. Error bars show 95% conﬁdence intervals.

 

 

 

Percent Flowering Plant Node Development

 

1 00%

75%

50%

25%

   

0% 0 Weeks 5C 15 Weeks SC
SD LD

 

 

 

 

SD LD SD LD
m 0 weeks 5C -15 weeks SC - Initial Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
250

200

 

150
100
50

   

0

m 0 weeks 5c - 15 weeks 5c m 0 weeks 5c - 15 weeks 5c

 

 

 

 

Number of Flowers Plant Height at Flower

Height (cm)

   

LD
m 0 weeks SC - 15 weeks SC m 0 weeks SC - 15 weeks 5C

 

 

 

 

 

 

Figure 34. Effects of photoperiod and cold treatment on Lewisia cotyledon as
indicated. Error bars show 95% conﬁdence intervals.

93

 

Percent Flowering

1 00%
75%
50%
25%

0%

SD LD
553 0 weeks SC -1Sweeks 5C

 

Plant Node Development
30

 

    

0 Weeks 5C

15 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud
100
80
60
40
20
O

 

SD
m 0 weeks 5c - 15 weeks 5c

Days to Flower

 

SD LD

m 0 weeks SC - 15 weeks SC

 

 

Number of Flowers

 

SD LD
m 0 weeks 5C - 15 weeks 5C

 

 

Plant Height at Flower

SD LD

 

m 0 weeks 5C - 15 weeks SC

 

 

Figure 35. Effects of photoperiod and cold treatment on Lychnis coronaria
'Angel Blush' as indicated. Error bars show 95% conﬁdence intervals.

94

 

Percent Flowering

1 00%

75%

50%

25%

 

0%

LD
m 0 weeks 5C -15 weeks SC

 

Plant Node Development

 

 

0 Weeks 5C 15 Weeks SC
LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud
70
60
SO
40
30
20
10

0

 

m 0 weeks 5c - 15 weeks so

 

Days to Flower

 

SD LD
m 0 weeks SC - 15 weeks SC

 

 

 

Number of Flowers

 

 

LD
m 0 weeks SC - 15 weeks 5C

 

 

 

Plant Height at Flower

50
40

Height (cm)
N 6)
O O

_L
O

 

0

SD LD
m 0 weeks 5C - 15 weeks SC

 

 

 

Figure 36. Effects of photoperiod and cold treatment on Oenothera fruticosa
'Youngii-Lapsley' as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

Percent Flowering Plant Node Development
25 ,

 

   

0 Weeks 5C 15 Weeks SC
SD LD

 

 

 

 

LD SD LD
m 0 weeks SC -15 weeks 5C - lnltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
120

100

     

 

 

 

 

so
so
40
20
0
SD LD SD LD
mOweeks Sc -15 weeks SC MOweeks SC -15weeks 5C
Number of lnflorescences Plant Height at Flower
4 4o
3 A so
E
.9.
2 E» 20
1 £ 10

   

0

SD LD

SD LD
m a weeks 5"; - 15 weeks 5c m 0 weeks SC - 15 weeks 5C

 

 

 

 

 

Figure 37. Effects of photoperiod and cold treatment on Polygonum afﬁne
'Dimity' as indicated. Error bars show 95% conﬁdence intervals.

96

 

Percent Flowering

1 00%

75%

50%

25%

 

0%
SD LD

m 0 weeks 5c -15 weeks 5c

 

Plant Node Development
25

 

 

0 Weeks 5C 15 Weeks 5C
LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud
80

60
40

20

 

0

SD LD
m 0 weeks 5c - 15 weeks 5c

 

Days to Flower

 

SD LD

Maweeks 5C -15 weeks SC

 

 

 

Number of Flowers

140
1 20
1 00
80
60
40
20

 

SD LD
m 0 weeks SC - 15 weeks 5C

 

 

 

 

Plant Height at Flower

35

30

A 25
20
15
10
5

Height (cm

 

m Oweeks 5C -15 weeks 5C

 

 

Figure 38. Effects of photoperiod and cold treatment on Potentilla atrosanguinea
'Miss Willmott' as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

Percent Flowering Plant Node Development
40 ,

 

 

1 00%

75%

50% ,,

25%

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0% 0 Weeks 5C 15 Weeks SC
SD LD SD LD SD LD
m 0 weeks 5C -15 weeks SC - Inltlal Nodes m Nodes at Flower
Days to Visible Bud Days to Flower
120
100
so
so
40
20
0
SD
m 0 weeks 5c - 15 weeks 5c m 0 weeks 5c - 15 weeks 5c
Number of Inﬂorescences Plant Height at Flower
20 100
15 A so
5 so
10 2’
g, 40
5 f 20 7
o 0
SD LD
EWOweeks SC -15weeks 5C mOweeks 5C -15weeks SC

 

 

 

 

 

 

Figure 39. Effects of photoperiod and cold treatment on Sidalcea ‘Party Girls' as
indicated. Error bars show 95% conﬁdence intervals.

98

 

Percent Flowering

1 00%

75%

50%

25%

 

0%
SD

m 0 weeks 5C -15 weeks SC

Plant Node Development
25

 

    

0 Weeks SC 15 Weeks SC
SD LD SD LD

- Inltlal Nodes ma Nodes at Flower

 

 

Days to Visible Bud

1 20
1 00
80
60
40
20
0

 

SD

5333 0 weeks 5c - 15 weeks 5c

 

Days to Flower

LD

m 0 weeks SC - 15 weeks SC

 

 

Number of Flowers

Plant Height at Flower

50
40

 

530
520
0

=10

   

0

SD

SD LD
m a weeks 5c -15 week, 5c m 0 weeks so - 15 weeks 5c

 

 

 

 

 

Figure 40. Effects of photoperiod and cold treatment on Stokesia Iaevis 'Klaus
Jellito' as indicated. Error bars show 95% conﬁdence intervals.

99

 

 

 

 

Percent Flowering Plant Node Development

100%¢

 

 

I————————————th———-——————-——#

75% _______

0.. ___—__—-4

use. ___—
eeo "‘

 

 

 

 

 

  

 

 

 

15 Weeks SC

0 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

SD LD
mOweeks 5c -15weeks 5c

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Days to Visible Bud Days to Flower
115 115
150 . ______________________ 5 150 ____________
125 ___________________ 125 ____________
1oo _________________ 100
75 i __________________ 75
50 ........ 50
25 ————— 25
o . 55:3: 0 .
LD SD
mllweekssc -15weeksSC ﬂaweeksSC -15weeksSC
Number of Flowers Plant Height at Flower
15 . 150
12 _ ________ ___ ____________ 125.
9 S100 ‘
I; 75«
6 g 50 ‘
3 25 ‘ see
0 6:3
LD

 

LD

SD

“Oweeks 5C -15 weeks 5C

m 0 weeks SC -15 weeks 5C

 

 

 

 

 

 

Figure 41. Effects of photoperiod and cold treatment on Tanacetum 'Robinson's
Dark Crimson' as indicated. Error bars show 95% conﬁdence intervals.

100

 

Percent Flowering

1 00%

75%

50%

25%

 

0%

SD LD
995 0 weeks 5c -15 weeks 5c

 

Plant Node Development

 

    

0 Weeks 5C 15 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud

1 60
120
80
40
0

SD LD
m 0 weeks 5C - 15 weeks 5C

 

Days to Flower

 

m 0 weeks 5C - 15 weeks SC

 

 

 

Number of lnflorescences
3

 

 

 

 

 

 

m 0 weeks SC - 15 weeks 5C

 

 

 

 

Plant Height at Flower

 

LD
m 0 weeks SC - 15 weeks SC

 

Figure 42. Effects of photoperiod and cold treatment on Thalictrum
aquilegifolium as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

 

 

 

      

 

 

 

 

 

 

 

   

        

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

Percent Flowering Plant Node Development
100% 25
20
75% 15
50% 1o - m.
25% 5
0% 0 Weeks 5C 15 Weeks SC
SD LD SD LD
m 0 weeks so -15 weeks so - Initial Nodes mNodes at Flower
Days to Visible Bud Days to Flower
4o 40
30 30 _7‘_ «an
20 20 ____ - _ _______
1o 10 ___- -_ _____
SD SD LD
m 0 weeks SC - 15 weeks 5C m 0 weeks 5C - 15 weeks 5C
Number of I nﬂorescences Plant HGith at Flower
12 20
A 15
E
O
E 10 ,
2
£ 5
SD LD
m 0 weeks 5c - 15 weeks 5c m 0 weeks 5C - 15 weeks SC

 

 

 

 

Figure 43. Effects of photoperiod and cold treatment on Tiare/la wherryi as
indicated. Error bars show 95% conﬁdence intervals.

102

 

 

Percent Flowering

1 00%

75%

50%

25%

 

0%
SD

m 0 weeks 5C -15 weeks 5C

 

Plant Node Development

 

 

 

0 Weeks 5C 15 Weeks SC
SD LD SD LD

- Initial Nodes ms Nodes at Flower

 

 

 

Days to Visible Bud
120
100

80
60
40
20

0

 

SD LD

m 0 weeks SC - 15 weeks SC

 

Days to Flower

 

SD LD

m 0 weeks 5C -15 weeks 5C

 

 

 

Number of Flowers

 

m 0 weeks SC - 15 weeks 5C

 

 

 

 

Plant Height at Flower
18
15

.5
N

Height (cm)
0 w a G9

 

SD LD
m 0 weeks SC -15 weeks SC

 

 

Figure 44. Effects of photoperiod and cold treatment on Tn'cyn‘is hirta 'Miyazaki'
as indicated. Error bars show 95% conﬁdence intervals.

 

 

 

 

Percent Flowering

1 00%

75%

50%

25%

 

0%

LD
m 0 weeks 5c -15 weeks 5c

 

Plant Node Development

 

 

 

  

 

 

   

0 Weeks SC
SD LD

  

 

1 5 Weeks SC
SD LD

- Inltlal Nodes m Nodes at Flower

 

 

Days to Visible Bud

1 20
1 00
80
60
40
20
0

 

 

 

 

 

 

 

SD LD
m 0 weeks SC -15 weeks 5C

Days to Flower

 

 

 

 

 

SD LD

m 0 weeks SC - 15 weeks 5C

 

 

Number of lnflorescences
20

16
12
B
4

 

LD
m 0 weeks SC - 15 weeks 5C

 

 

 

Plant Height at Flower

50 ,

Height (cm)
M u b
O O O

_L
O

 

O

 

D
m 0 weeks 5C -15 weeks SC

 

 

Figure 45. Effects of photoperiod and cold treatment on Veronica Iongifolia
'lcicle' as indicated. Error bars show 95% conﬁdence intervals.

 

 

Percent Flowering

1 00%

75%

50%

25%

 

0%
SD

R!!! 0 weeks 5C -15 weeks 5C

 

Plant Node Development

 

 

0 Weeks 5C 15 Weeks SC
SD LD SD LD

- Inltlal Nodes m Nodes at Flower

 

 

 

Days to Visible Bud

60
50
40
30
20
1 0

0
SD LD

m 0 weeks 5c - 15 weeks 5c

 

 

Days to Flower

SD LD

m 0 weeks 5C - 15 weeks 5C

 

 

 

Number of lnflorescences
10

 

ON#Q@

 

LD
m 0 weeks 5C - 15 weeks 5C

 

 

 

Plant Height at Flower
35
30

A25
5,20
315

£10
5

 

SD LD
m 0 weeks 5C -15 weeks 5C

 

 

 

Figure 46. Effects of photoperiod and cold treatment on Veronica Iongifolia 'Red
Fox' as indicated. Error bars show 95% confidence intervals.

 

APPENDIX B:

EFFECTS OF FORCING TEMPERATURE

106

 

 

 

INTRODUCTION

Timing is just as important as a high quality crop in the ﬂoriculture
industry. As most commercial growers must produce their crop on a strict
schedule, knowing how long it takes for a plant to reach a saleable stage is
crucial. Temperature is known to affect both the quality and the rate of
development in plants, and is the most commonly used method of regulating
timing in greenhouse crops. By testing today’s popular new herbaceous
perennials for their responses to different forcing temperatures, we can make
recommendations as to what temperatures will produce the highest quality crop
in the fastest time.

As most of the species we work with require or beneﬁt from a cold
treatment, species in the temperature experiment spend ~12 weeks in the cooler
at 5°C. They are then potted up and placed in greenhouses at ﬁve different
temperatures ranging from 17-29°C. Data taken includes such standard
information as date of visible bud and ﬂower, height at bloom, and the number
and size of ﬂowers. Buds are measured every 3-4 days as they expand to
provide a yardstick for ﬂower development. General health and appeal of the
plants under different temperatures is also noted.

‘ The temperature experiment provides basic timing information for growers
new to a crop, or those wishing to improve plant quality. Bud measurements
help growers to gauge the progress of plants towards ﬂower, so they can adjust
temperatures to meet scheduling requirements. Researchers also use this

information as a reference in planning other experiments using these species.

107

 

 

 

PROTOCOL
OBJECTIVE: To quantify the inﬂuence of forcing temperature on plant quality
and time to visible bud and ﬂower.
EXPERIMENTAL DESIGN:
Plant Material: See Table 10

Cold treatment prior to forcing:
12 weeks at 5°C (9-h photoperiod from cool-white ﬂuorescent light)

Forcing environment:
1) Photoperiod:
NI from 2200 to 0200 HR with incandescent lamps (1"t year)
16-hr day extension with high-pressure sodium lamps (2"d year)
2) Temperature:
17, 20, 23, 26 or 29°C

Plant Requirements:
10 plants x 5 temperatures =50 plants/species

RESEARCH PROTOCOL:
Plants will be cooled for 12 weeks before being potted into 5"

square pots. Cooled plants will be placed in the above temperature treatments

and forced under long days, provided either by day extension to 16 hrs, or a 4-h

night interruption. Data collected will include:

1) Initial leaf count

2) Date of visible bud/inﬂorescence

3) Bud length or diameter every three to ﬁve days, where appropriate
4) Date of ﬂowering

5) Final leaf number at date of ﬂowering

6) Number of ﬂower buds/inﬂorescences at date of ﬂowering

7) Height of plant/inﬂorescence at date of ﬂowering

8) Flower diameter at anthesis, where appropriate

9) Date of ﬁrst color, where appropriate

10) Number of ﬂowering stalks, where appropriate

108

 

 

1i. "

Table 10. Effects of Forcing Temperature. Production information, including
year included in experiment, weeks of cold given, approximate weeks to ﬂower at
17-29°C, and comments on plant quality and other observations. Recom-
mended temperature range represented by bold numbers in the weeks to ﬂower
columns.

 

 

wks" weeks to ﬂower at: if i

Comments *
°°'d 7 20 23 26 29 ‘

Astilbe chinensis 1st 18 14 12 11 1o 10 prefers °°°'e”° m"? o !
pumila 2nd 12 12 11 10 11 range temps, ﬂowenng/o

very low at 29°C E

prefers cooler temps; >
ﬂower size and number

 

' Species/Cultivar year

 

Campanula ‘Birch 1“ 16 5.1 4.2 4.0 3.6 6.4

 

 

 

 

 

 

. , M
Hybrid 2 12 7.4 5.6 4.7 5.0 7.3 was best at 17°C i
Coreopsis verticillata 1':t 12 10 9 7 7 6 3:32:23; tzrgsfnore .
‘Moonbeam' 2"(1 12 9 s 7 6 6 9 i

ﬂowers at low temps
Delphinium taller but sturdier, with ‘
grandiﬂorum 1”t 16 9.2 8.2 7.6 7.7 8.4 larger ﬂowers at low I
I ‘Blue Mirror’ Flﬁtemperatures i
l
Geranium 1st 16 6.9 5.9 4.3 4.6 4.9 3255339353522: with l
s M :
xdalmatlcum 2 12J 8.3 6.5 5.7 5.7 8.4 more ﬂowers 1
little effect on ﬂower size;

 

Hemerocallis . 2"d 12 11 8 7 7 8 more ﬂowers at lower !

Stella de Oro e
temperatures 1

Hibiscus thbn'da prefers higher temps;

1“t 0 14 14 9 8 7 plantqualityverylowat
17°C

I

|

‘Disco Belle Mix’
cooler temps produce a i

1

 

Monarda didyma

nd .
‘Gardenview Scarlet’ 2 12 10 9 9 8 10 taller, but much sturdler

plant with more ﬂowers

 

 

   
   
  
   

Phlox paniculata 1st 19 11 1o 9 s s Stems Sturd'e'and p'ants

‘Eva Cullum’ 2"d 12 13 12 11 11 10 "we “rammed at°°°'e'
temperatures

bud development in the
2"d 12 2.5 2.2 1.7 1.5 1.5 cooler; very little effect of
forcm temperature
temp had little effect 0
plant quality; a bit

 

Phlox subulata
“Emerald Blue’

 

 

‘ , 1St 16 13 12 11 11 13
iSedum Autuanoy 2..., ”J13 12 12 13 14

 

 

 

 

 

 

 

 

 

109

 

 

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Bud number
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Nodes formed during forcing

O)
O
J

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01
O

 

h
0
-l
I
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O

 

 

 

 

N
O
..—
.-

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O
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1‘6 1'8 2'0 2'2 2'4 2'6 28 30

Temperature (°C)

Figure 49. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Astilbe
chinensis pumila in year 1. Error bars show standard deviation.

112

 

I?

 

 

 

 

 

 

 

 

Bud number
00

 

 

O

 

—L
N

 

 

_s
O
l
i
l

 

 

 

 

 

Nodes formed during forcing

omeoaoo

 

 

 

Plant height (cm)
8 8 ‘5

 

 

_s
O

 

 

 

16 18 20 22 24 26 28 30

Temperature (°C)

Figure 50. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Astilbe
chinensis pumila in year 2. Error bars show standard deviation.

113

 

 

 

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Temperature (°C)

Figure 53. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for
Campanula 'Birch Hybrid' in year 1. Error bars show standard deviation.

116

 

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Temperature (°C)

Figure 54. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Campanula 'Birch Hybrid'
in year 2. Error bars show standard deviation.

117

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 55. Relationship between bud diameter and number of days before ﬂower
for Campanula 'Birch Hybrid' in year 1. Actual temperatures for the indicated
treatments are from average date of visible bud to average date of ﬂower.

118

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 56. Relationship between bud diameter and number of days before ﬂower
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treatments are from average date of visible bud to average date of ﬂower.

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Temperature (°C)

Figure 58. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Delphinium grandiﬂora
'Blue Mirror' in year 1. Error bars show standard deviation.

121

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 59. Relationship between bud diameter and number of days before ﬂower
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indicated treatments are from average date of visible bud to average date of ﬂowe

122

 

 

 

 

 

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Temperature (°C)

Figure 62. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬂrstﬂower for
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Temperature (°C) Temperature (°C)
Figure 63. Inﬂuence of forcing temperature on plant height, number of nodes
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stalks per plant, and number of ﬂowers per stalk for Geranium dalmaticum in
year 2. Error bars show standard deviation.

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Figure 64. Relationship between bud diameter and number of days before ﬂower
for Geranium dalmaticum. First year data represented by circles, second year
data represented by triangles. Actual temperatures for the indicated treatments
from average date of visible bud to average date of ﬂower were 29.4, 25.8, 23.1,
19.9, and 17.6°C for the ﬁrst year and 28.7, 25.9, 22.2, 19.5, and 17.4°C for the
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Figure 66. Inﬂuence of forcing temperature on plant height, number of nodes

formed during forcing, diameter of open ﬂowers, number of ﬂowers, number of

stalks per plant, and number of ﬂowers per stalk for Hemerocallis 'Stella‘de Oro'
in year 2. Error bars show standard deviation.

129

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 67. Relationship between bud diameter and number of days before ﬂower
for Hemerocallis 'Stella de Oro' in year 2. Actual temperatures for the indicated
treatments are from average date of visible bud to average date of ﬂower.

130

 

 

 

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Figure 69. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
' diameter, and plant height measured at ﬁrst ﬂower for Hibiscus 'Disco Belle Mix'
in year 1. Error bars show standard deviation.

132

 

 

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Figure 70. Relationship between bud diameter and number of days before ﬂower
for Hibiscus 'Disco Belle Mix' in year 1. Actual temperatures for the indicated
treatments are from average date of visible bud to average date of ﬂower.

133

 

 

 

 

 

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Temperature (°C)

Figure 73. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Phlox paniculata 'Eva
Cullum' in year 1. Error bars show standard deviation.

136

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Temperature (°C)

Figure 74. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Phlox paniculata 'Eva
Cullum' in year 2. Error bars show standard deviation.

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Temperature (°C)

_ Figure 76. Inﬂuence of forcing temperature on number of ﬂower buds, ﬂower
diameter, and plant height measured at ﬁrst ﬂower for Phlox subulata 'Emerald
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Temperature (°C)

Figure 79. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Sedum
'Autumn Joy' in year 1. Error bars show standard deviation.

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Figure 80. Inﬂuence of forcing temperature on number of ﬂower buds, number of
nodes formed during forcing, and plant height measured at ﬁrst ﬂower for Sedum
'Autumn Joy' in year 2. Error bars show standard deviation.

143