INFLUENCE OF GREENHOUSE
ENV!RONMENTAL FACTORS ON THE
FORCING 0F DAHLIA VARIABIUS WILLD.

Thesis for the Degree of M. S.
MICHIGAN. STATE UNIVERSITY
MARCIA DURSO
1976

 

ABSTRACT

INFLUENCE OF GREENHOUSE ENVIRONMENTAL FACTORS
ON THE FORCING OF DAHLIA VARIABILIS WILLD.

 

BY

Marcia Durso

Dutch—grown tuberous-roots of 'Park Princess' and
'Kolchelsee' were forced under various greenhouse conditions
during February, March, and April of 1975 and 1976. The
basic factors investigated were (a) fertilization, (b) tem-
perature, (c) light intensity, (d) photOperiod, and (e)
hydrogel. In all experiments, ancymidol was applied for
height control two weeks after the respective planting dates
at the rate of 0.5 mg per 15 cm pot. Except for the ferti-
lization experiments, Osmocote (14-14-14) was either
incorporated at a rate of 169 g per cubic foot or t0p
dressed at a rate of 9 g per pot. Unless the objective was
to evaluate the individual factor, full sunlight, natural
daylength, and a minimum night temperature of 17°C were used.

The statistical parameters were days to flower,
flower diameter, flower longevity, plant height, the number
of flowers and buds per plant, and the number of shoots per

plant.

Marcia Durso

Applications of various formulations of Osmocote or
20-20-20 as a soluble fertilizer produced high quality
plants which flowered in approximately 70 days. This was
an average of 20 days earlier than non—fertilized plants.
More importantly, the number of plants flowering was
increased. Without fertilization, many plants either failed
to flower or produced only a few abnormal flowers. Over the
two year period, with 'Kolchelsee', the number of plants
flowering was increased from 25% to 100% and with 'Park
Princess' the increase was from 85% to 100%.

The earliest flowering (59 days) was obtained with
a day/night temperature of 29/22°C. As day/night tempera-
tures were lowered to 29/17 and 27/12°C, the days to
flower increased to 63 and 90 days, respectively. Plants
grown at 27/16°C averaged 78 and 86 days to flower for
'Kolchelsee' and 'Park Princess', respectively. The best
height control was obtained at 27/16°C with heights of 34
and 30 cm for 'Kolchelsee' and 'Park Princess', respectively.
Plants at 29/17°C were approximately 4 cm taller and at
27/12°C plants were 9 cm taller. At 29/22°C they were
stunted and chlorotic, and averaged 27 cm. It was concluded
that dahlias responded to both day and night temperatures.
The optimum day/night temperature combination appeared to be
27/16°C.

When light intensity was reduced by 50%, the plants
were 11 cm taller than those receiving either 100 or 75%

light levels. All other parameters were not significantly

Marcia Durso

affected. Apparently when dahlias are forced in a greenhouse
they require very high light intensities.

Plants given an eight hour photoperiod were 17 days
earlier in flowering than all other treatments, but only 40%
of the plants flowered. At anthesis, the flowers which did
develop were abnormal. They had 'open-eye' centers. Under
natural photoperiods flowering averaged 69 days. Long day
treatments of either the 16 hour photoperiod or the 4 hour
night break caused a delay of 6 days. Plant heights were
satisfactory for all treatments except under the eight hour
photoperiod. 'Kolchelsee' averaged 26 and 33 cm and 'Park
Princess' averaged 29 and 30 cm in 1975 and 1976, respec-
tively. Other parameters were not consistently affected by
the treatments. Therefore, dahlias should never be forced
under an 8 hour photoperiod. Forcing under an increasing
natural daylength of 10 to 14 hours provided the best results.

Hydrogel did not influence flowering or developmen-

tal rates and all plants were of satisfactory quality.

INFLUENCE OF GREENHOUSE ENVIRONMENTAL FACTORS

ON THE FORCING OF DAHLIA VARIABILIS WILLD.

 

BY

Marcia Durso

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1976

ACKNOWLEDGMENTS

I wish to thank Dr. August De Hertogh for his contin-
ual interest and suggestions during this study. I also
extend thanks to Drs. Shigemi Honma, Aleksander Kivilaan,
and J. C. Raulston for their assistance in the preparation
of this manuscript. The help of Mr. Norman Blakely is also
appreciated.

The financial assistance of the Netherlandstlower-

bulb Institute is gratefully acknowledged.

ii

TABLE OF CONTENTS

Page

LIST OF TABLES O O O O O O O O 0 O O O O O V
LIST OF FIGURES O O O O O O O O O O O O 0 ix
INTRODUCTION . . . . . . . . . . . . . . 1
REVIEW OF LITERATURE. . . . . . . . . . . . 3
Introduction. . . . . . . . . . . . . 3
Botanical History . . . . . . . . . . . . 4
Production Cycle . . . . . . . . . . . . 5
Deve10pmental Stages . . . . . . . . . . . 6
Fertilization O O O O O O O O O O O O O 6
Temperature . . . . . . . . . . . . . . 8
Light IntenSity O O O O O O O O O O 0 O O 12
PhotoperiOd O O I O O O O O O O O O O 0 13
Growth Regulators . . . . . . . . . . . . 19
MATERIALS AND METHODS . . . . . . . . . . . 21
Fertilizer Experiments . . . . . . . . . . 25
Temperature Experiments . . . . . . . . . . 26
Light Intensity Experiments. . . . . . . . . 26
Photoperiod Experiments . . . . . . . . . . 28
Hydrogel Experiment . . . . . . . . . . . 30
Pesticide Usage. . . . . . . . . . . . . 31
Removal of Failures . . . . . . . . . . . 32
Data Collection. . . . . . . . . . . . . 32
Statistical Analysis . . . . . . . . . . . 33
RESULTS AND DISCUSSION . . . . . . . . . . . 35
Forcing Criteria . . . . . . . . . . . . 35
Effects of Fertilization. . . . . . . . . . 36
Effects of Temperature . . . . . . . . . . 43
Effects of Light Intensity . . . . . . . . . 55

iii

Page

Effects of Photoperiod. . . . . . . . . . . 65
Effects of Hydrogel. . . . . . . . . . . . 77
CONCLUSIONS 0 O O I O O I O O O O O O O O 8 0

LITERATURE CITED . . . . . . . . . . . . . 82

iv

Table

1.

LIST OF TABLES

Page

Mean day/night temperatures during the 1976
forcing period. . . . . . . . . . . 27

Foot candle measurements of the three light
intensity levels under different weather
conditions and dates, 1976. . . . . . . 27

Solar radiation in calories/cmZ/day at East
Lansing, Michigan. . . . . . . . . . 28

Calories/cmz/day determinations under three
weather conditions at East Lansing,
MiChigan. O O O O O O O O O O O O 28

Number of daylight hours and times of
photoperiod treatments for dates during
the 1976 forcing season at East Lansing,
Michigan, 43° north latitude . . . . . . 30

Effect of fertilizer treatments on the number
of days to flower, plant height, flower
longevity, and diameter of the first three
flowers and number of shoots produced per
plant of 'Kolchelsee'. Tuberous-roots were
planted on 4 February, 1975 . . . . . . 39

Effect of fertilizer treatments on the number of days
to flower, plant height, flower longevity, and
diameter of the first three flowers and number
of shoots produced per plant of 'Park Princess'.
Tuberous-roots were planted on 4 February,

1975 . . . . . . . . . . . . . . 40

Effect of fertilizer treatments on the number
of days to flower, plant height, flower
longevity, and diameter of the first three
flowers and number of shoots produced per
plant of 'Kolchelsee'. Tuberous-roots were
planted on 6 February, 1976 . . . . . . 41

Table Page

9. Effect of fertilizer treatments on the
number of days to flower, plant height,
flower longevity, and diameter of the first
three flowers and number of shoots produced
per plant of 'Park Princess'. Tuberous-roots
were planted on 6 February, 1976. . . . . . 42

10. Effect of temperature on the number of days to
flower, plant height, flower longevity, and
diameter of the first three flowers and number
of shoots produced per plant of 'Kolchelsee'.
Tuberous-roots were planted in 1975. . . . . 44

11. Effect of temperature on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers and
number of shoots produced per plant of
'Park Princess'. Tuberous-roots were planted
in 1975 . . . . . . . . . . . . . . 46

12. Effect of temperature on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers
and number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were planted
in 1976.. . . . . . . . . . . . . . 49

13. Effect of temperature on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers
and number of shoots produced per plant of
'Park Princess'. Tuberous-roots were
planted in 1976 . . . . . . . . . . . 51

14. Effect of light intensity on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers
and number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were
planted in 1975 . . . . . . . . . . . 56

15. Effect of light intensity on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers
and number of shoots produced per plant of
'Park Princess'. Tuberous-roots were
planted in 1975 . . . . . . . . . . . 58

vi

Table Page

16. Effect of light intensity on the number of
days to flower, plant height, flower longevity,
and diameter of the first three flowers and
number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were planted
in 1976. . . . . . . . . . . . . . 60

17. Effect of light intensity on the number of
days to flower, plant height, flower longevity,
and diameter of the first three flowers and
number of shoots produced per plant of
'Park Princess'. Tuberous-roots were
planted in 1976 . . . . . . . . . . . 62

18. Effect of phot0period on the number of days to
flower, plant height, flower longevity, and
diameter of the first three flowers and number
of shoots produced per plant of 'Kolchelsee'.
Tuberous-roots were planted in 1975 . . . . 66

19. Effect of photoperiod on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers and
number of shoots produced per plant of
'Park Princess'. Tuberous-roots were
planted in 1975 . . . . . . . . . . . 68

20. Effect of photoperiod on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers and
number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were
planted on 9 February, 1976 . . . . . . . 70

21. Effect of photOperiod on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers and
number of shoots produced per plant of
'Park Princess'. Tuberous-roots were
planted on 9 February, 1976 . . . . . . . 72

22. Effect of hydrogel on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers
and number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were planted
on 4 February, 1975. . . . . . . . . . 78

vii

Table Page

23. Effect of hydrogel on the number of days
to flower, plant height, flower longevity,
and diameter of the first three flowers
and number of shoots produced per plant
of 'Park Princess'. Tuberous-roots were
planted on 4 February, 1975. . . . . . . 79

viii

LIST OF FIGURES

Figure Page

1. A tuberous-root of 'Kolchelsee' planted
in the 15 cm pot. . . . . . . . . . . 24

2. A high quality plant of 'Park Princess'
after forcing. . . . . . . . . . . . 38

ix

INTRODUCTION

Dahlias (Dahlia variabilis Willd.) grown from

 

tuberous-roots are popular with amateur flower growers and
home gardeners (James, 1963). The use of dahlias could be
increased by marketing them as flowering plants at Easter
and Mother's Day. Initially, the plants would be used as
house plants and later they could be transplanted into out-
door flower beds, or large containers where they would
continue flowering until the first killing frost.

The production of greenhouse cr0ps is based on con-
trolling the major environmental factors which influence
plant growth and development. Light is an important factor
because of its influence on plant growth and development and
because it is required for photosynthesis. The effects of
light intensity and duration (photoperiod) vary with the
species and many times even the cultivar. Maximum, minimum,
and Optimum levels have been established for many crops
(Einert and Box, 1967, Smith and Langhans, 1962b).

Temperature affects plant quality and flower develop-
ment of many plant species (Smith and Langhans, 1962a, Roh

and Wilkins, 1973). Since night temperature generally

affects growth more than day temperature, minimum night
temperatures have been established for many greenhouse crOps
(Cathey, 1954, Langhans and Larson, 1960).

Because the production of plants in pots restricts
root development to a finite soil volume, fertilization
requirements for a crop are also quite specific (Ball, 1972,
Gortzig, 1974). '

Forcing schedules must integrate these factors so
that the crop will flower uniformly within a pre-determined
number of days and at a specific plant height. The number
of flowers per plant and flower life and diameter also must

fall within desired ranges.

Chemical growth retardants have been utilized to

 

reduce the height of many crops, including Chrysanthemum,

Lilium, and Euphorbia (Gortzig, 1974). Ancymidol has been

 

effective on a wide range of crops (Einert, 1971, Larson

and Kimmins, 1972, Cathey and Heggestad, 1973) and its
effects on tuberous-rooted dahlias have been demonstrated
(De Hertogh, Blakely, and Szlachetka, 1976). With appropri-
ate application procedures, heights of 30-40 cm have been
achieved with selected cultivars. Thus, the potential for
forcing dahlias as potted plants has been established.

The objective of this study was to determine the
effects of fertilization, greenhouse temperature, photoperiod,
and light intensity on the forcing of two tuberous-rooted
cultivars, and to integrate them into a basic greenhouse

program for forcing pot dahlias.

REVIEW OF LITERATURE

Introduction

 

Several studies have been conducted on the effects
of environmental factors on the growth of dahlias. The
objectives of the studies varied widely and the cultivars
were always different. They were primarily designed to
evaluate tuberization effects, cut flower production, or
outdoor growing conditions. Responses of the different
cultivars indicated that this was a major source of vari-
ability. In addition, the plant materials used included
seedlings, stem cuttings, and tuberous-rooted plants.

The effects of photoperiod treatments were first
reported (Garner and Allard, 1923, Zimmerman and Hitchcock,
1929) on the tuberization process. Effects on flowering
were reported later (Maatsch and Rfinger, 1954, Yasuda and
Yokoyama, 1960). Most experiments included a natural day-
length treatment. Since the research had been conducted in
Germany, the Netherlands, England, Japan, and the United
States, seasonal conditions of temperature, daylength, and
light intensity varied greatly. Planting and harvesting

dates were likewise different.

There are few reports available on the effects of
other environmental factors on the growth of dahlias. The
effect of light intensity was determined on stock plants
used for cutting production but not on forced flowering
plants (Biran and Halevy, 1973a). Experiments to determine
the response to different temperatures during the forcing
period have not been conducted. Fertilization requirements
have never been evaluated in a forcing program.

The basic responses of dahlias as well as some
analogous bulbous plants to environmental factors are the
subjects of this review of literature. For clarity, the
botanical history, production cycle, and a summary of the

development stages of the dahlia are also included.

Botanical History

 

Dahlias are native to the high plateau regions of
Mexico and Guatemala (James, 1963). They are half-hardy,
herbaceous, tuberous-rooted perennials. The genus Dahlia,
named for Andreas Dahl, is a member of the Compositae family,
forming both disc and ray florets. Leaves are opposite.

As early as 1580, Hernandez described cultivated
dahlias in Mexico using the Aztec names of Acocotli,
Cocoxochitl, and Acocoxochitl which referred to the hollow
stem characteristic. He described several different forms
of dahlias having variations in petal color and plant heights.

In 1789, seeds from Mexico were introduced to Spain

and in 1798 subsequently to England. Because of the Mexican

origin, dahlias were assumed to be subtrOpical, but they did
not respond accordingly. By 1804, Q. coccinea, 2. crocea,
Q. purpurea, and Q. rosea were recognized as species and

hybrid forms were listed in the Annual Dahlia Register in

 

1836. In 1872, the first cactus dahlia, later named Dahlia

Juarezii was sent from Mexico to M. J. J. VanderBerg near

Utrecht, the Netherlands (Baumgardt, 1970, James, 1963).
Dahlias are now produced in England, The Netherlands,

and in several areas of The United States.

Production Cycle

 

To produce tuberous-rooted dahlias (Krabbendam, 1967)
mother plants of each cultivar are planted in 15-20 cm deep
benches in 15°C greenhouses in late January or February. As
shoots develop from the base of the previous year's stem
(crown), cuttings are removed when they are 7 to 10 cm long.
It is essential that each cutting include a portion of the
crown or otherwise the plant will not produce shoots in the
second growing season. Cuttings are taken through early May.
The cuttings are rooted in sand under greenhouse conditions
and are subsequently placed in cold-frames until planting
into the field in early June. Throughout the summer months,
shoot growth occurs and tuberization is induced by the
ensuing short days of fall. After the first frost, normally
October, all shoot portions of the plants are cut off and
the tuberous-roots are harvested. They are kept in high

humidity, nonventilated storage rooms at 9-11°C. Prior to

shipping, they are graded, washed, and packed in peat or

some similar material.

Developmental Stages

Only one study (Krijthe, 1938) has been carried out
on the formation and development of leaves and flowers of
the dahlia roots during and after the storage period. She
found that no flowers had been initiated in Mignon dahlia
‘L'Innocence' by May 8, the date of planting of the tuberous-
roots in the field. After two and a half weeks and the
formation of seven pairs of leaves, flower initiation
occurred. Flowering occurred some ten weeks after planting.
Tuberous-roots planted in a greenhouse in early March and
grown at 15-16°C started flower initiation after the forma-
tion of only five pairs of leaves. When the temperature was
raised to 20°C on March 25, flowering also occurred about
ten weeks after planting (about mid-May). Krijthe (1938)
also observed that height at flowering was dependent upon
the length of the internodes. The control of the length of
the internodes is the important key in producing dahlias as

pot plants.

Fertilization

 

Fertilization has been recommended for dahlias grown
in the garden from tuberous-roots, cuttings, or seedlings.

Baumgardt (1970) and Vance (1974) have pr0posed using liquid

feed applications every two weeks or dry formulations of
(2-10-6) or (8-20-12) at the rate of 453 g per 9.2 square
meters.

Specific fertilizer recommendations for greenhouse
forced dahlias have not been established. De Hertogh,
Blakely, and Szlachetka (1976) used liquid applications of
30 ppm (20-20-20) every three weeks in their growth regula-
tor trials. In evaluating the effects of growth regulators
on tuberization, rooted cuttings of 'Nita' were fertilized
weekly with a 12% solution of (20-8.6-16.6) NPK (Read,
Dunham, Fieldhouse, 1972).

Some bulbous plants have variable fertilizer require-

ments during forcing. Tulipa, Hyacinthus and Narcissus are

 

 

 

not normally fertilized during the forcing period (De Hertogh,
1973) but regular fertilization has been recommended for

forcing Lilium longiflorum (Kiplinger and Langhans, 1967).

 

Constant liquid feed applications at the rates of 150 ppm
'nitrogen throughout the greenhouse forcing period or weekly
applications of 90 g per 38 liters of water of potassium
nitrate alternated with calcium nitrate have been suggested
(Kiplinger and Langhans, 1967). Osmocote (12-0-41) or (26-
0-0) incorporated into the planting media at the rates of
97.6 or 131 g per cubic foot caused rapid emergence and
earlier maturity in forced 'Ace' lilies although bud initi-
ation and bud counts were only minimally affected (Hasek and

Sciaroni, 1970).

Corms of Gladiolus 'Spotlight' pot-forced in sand

 

from May to August flowered about five days earlier when
treated with nitrogen at rates of 100 or 200 ppm nitrogen
and phosphorus at 50 ppm, while plants not receiving nitrogen

flowered later (Kosugi, 1960).

Temperature

 

Temperature is an important factor both in the
storage of bulbous plant materials and during forcing
(De Hertogh, 1973).

For dahlias, studies were conducted to determine
the Optimal temperatures for the over-wintering of the
tuberous-roots for later use in the garden. Tuberous-roots
of three dahlia cultivars were stored satisfactorily from
November to May at temperatures of 1.7-10°C (Zimmerman and
Hitchcock, 1932). Dahlias stored at 0°C were infected with
soft rot while at 21-32°C, roots became desiccated and only
50% were viable when planted in the spring. Allen (1937)
confirmed these findings with seven other cultivars. He
found that the ideal temperature for a six month storage
period was 4.5-7.0°C with a relative humidity of 80 to 85%.
Peat moss with a moisture of 50% was an ideal packing
material to prevent desiccation. Higher moisture content of
the peat promoted disease development.

Temperature has a major influence in the forcing of

both bulbous and non-bulbous plant material (Hartsema, 1961,

De Hertogh, 1973). Its primary effect has been to accelerate
or delay the flowering process but other growth parameters
are also affected.

To date, there has not been a study on the effects
of greenhouse temperatures on forced dahlias. In their
experiments De Hertogh, Blakely, and Szlachetka (1976) used
the day/night temperature sequence of 16-17/18-20°C for
forcing several cultivars of tuberous-rooted dahlias from
February or March to May. Under these conditions,
'Kolchelsee' and 'Park Princess' flowered in 81 and 71 days,
respectively.

Flowering of dahlia seedlings (Botacchi, 1958) of
'Coltness' was reported in 141, 150, 149, 168, and 177 days
at 10°C under photoperiods of 9, 13%, 14%, 10%-16, 17%, and
24 hours respectively, while at 15.5°C flowering under the
same phot0periods was reported in 125, 120, 174, 134, and
155 days. Seedlings of 'Unwin' flowered in 138, 149, and
158 days at 10°C and 127, 135, and 135 days at 15.5°C under
photoperiods of 13%, 14', and 17% hours, respectively. For
both cultivars, plant heights at the 15.5°C treatment were
increased approximately 6 cm. At 21.1°C, 'Unwin' flowered
in 91 and 104 days with 9 and 14% hour photoperiods while
'Coltness' averaged 80 and 101 days at the same temperature
and photoperiods.

The effects of greenhouse temperatures on the days
to flowering and plant height at flowering have been

reported for a number of bulbous greenhouse crops.

10

Smith and Langhans (1962a) showed that both night
and day temperatures affected the number of days from plant-
ing to flowering of precooled 'Croft' lily bulbs but con-
cluded that night temperature had the greatest influence.
Plants at 10.0, 15.6, 18.3 21.1, and 26.7°C minimum night
temperatures flowered in 141, 110, 106, 95, and 82 days
respectively, with a 15.6°C day temperature, and they
flowered in 135, 102, 106, 86, and 81 days respectively with
a 21.1°C day temperature. The optimum continuous forcing
combination was the 21.1 day/15.6°C night temperature.

Plant height was also modified by the temperature regimes.
Heights were 35.6, 40.4, 39.3, 47.5 and 58.9 cm for constant
day/night temperatures of 10, 15.6, 18.7, 21.1 and 26.7°C,
respectively (Smith and Langhans, 1962a). With different
day/night temperatures, heights varied but the plants

tended to be tallest in treatments combining both high day
and high night temperatures and shortest with low day/night
temperatures.

Day and night temperatures during forcing from the
visible bud stage to anthesis affected the number of days
to flower in 'Ace' lilies (Roh and Wilkins, 1973). With
constant temperatures of 15.6, 21.1, 26.7 and 32.2°C,
flowering occurred in 45, 28, 25 and 24 days, respectively.
With a day temperature of 21.1°C flowering occurred in 40,
28, 26, and 28 days with night temperatures of 15.6, 21.1,

26.7 and 32.2°C, while with a day temperature of 26.7°C

ll

flowering was obtained in 30, 26, 25, and 23 days with the
same night temperatures. The forcing temperatures also
affected the plant heights at flowering. With a day tempera-
ture of 26.7°C, heights were 26.9, 23.5, 23.7 and 23.2 cm
for the respective night temperatures of 15.6, 21.1, 26.7,
and 32.3°C. Thus, plant height increased with the combined
high day and low night temperature.

Following pretreatments at 31°C and preparation

treatment at 13°C (Hartsema, 1961), bulbs of Iris hollandica

 

'Wedgewood' flowered in 58, 48, 35, and 31 days when forced
at constant temperatures of 15, 17, 20, and 23°C, respec-

tively. Flowering of Iris hollandica 'Dominator', ‘Professor

 

Blaauw', and 'Imperator' was accelerated by forcing at
increasing temperatures in the range of 9-18°C (Fortanier
and Zevenbergen, 1973). At 9°C, 50% flowering of the first
bud was seen in 142, 152, and 160 days, for the respective
cultivars while at 15°C the numbers of days decreased to
70, 85, and 111. At 18°C, 50% flowered in 59, 65, and 86
days while further decreases to 49, 50, and 73 days were

seen at 24°C. In forcing Iris hollandica 'Wedgewood' at

 

21, 18, and 15°C, stem lengths were increased from 12 to 19
and 34 cm, respectively under a 12 hour photOperiod while
with a 16 hour photoperiod at the same temperatures heights
were 26, 27, and 54 cm (Fortanier and Zevenbergen, 1973).
Thus, for out flower production it is important to select a
temperature which gives the most rapid flowering but with a

satisfactory length.

12

Light Intensity

 

The effect of light intensity on the stimulation of
rooting of dahlia cuttings was investigated by Biran and
Halevy (1973a). They found that the rooting percent of
cuttings from 'Orpheo' stock plants grown continuously under
only 50 or 28% of natural daylight was increased, but there
were 40% fewer cuttings per plant. Rooting was not enhanced
when stock plants were shaded only during the noon hours.
These treatments also affected the internodal lengths of the
cuttings. With 100, 50, and 28% light treatments, the
lengths of the second internodes were 1.8, 3.6, and 6.7 cm,
respectively.

The elongating effect of low light intensities dur-

ing the greenhouse forcing phase of Lilium longiflorum has

 

been established (Kohl and Nelson, 1963, Einert and Box,
1967). Under 500 ft. candles, 'Ace' lilies at full bloom
were significantly longer (79 cm) than those obtained with
a light intensity level of 1,000 ft. candles (65.7 cm).
This increase in height was due to internode length and not
the number of nodes (Kohl and Nelson, 1963).

Similarly, plants of the Harson strain of 'Georgia'
lilies forced under 100% light intensity were 38.6 cm in
height, while with 75 and 50% light, the height increased
to 44.5 and 47.5 cm, respectively (Einert and Box, 1967).
Flowering was also affected by these treatments. The flower
buds formed per plant numbered 13.3, 12.7, and 11.9 for the

100, 75, and 50% light intensities, respectively.

13

During outdoor summer forcing of Gladiolus 'Sans

 

Souci' (Shillo and Halevy, 1976a), a 25% light treatment
increased flower stalk length by 18 cm but decreased the
percent flowering to 64 and decreased the florets per spike
by 53%. With a 20% light treatment during winter forcing
the flowering of 'Dr. Fleming' was similarly decreased to

25% and the number of florets was decreased by 54%.

PhotOperiod

 

Tuber and tuberous-rooted plants progress through a
series of developmental stages. Normally, the sequence is
vegetative growth, then flower initiation and flowering, and
then tuber formation and enlargement. PhotOperiod treat-
ments have been shown to induce or retard the onset of the
different stages (Garner and Allard, 1923). Several reports
have established that the tuberization process in dahlias is
under short day control (Garner and Allard, 1923, Zimmerman
and Hitchcock, 1929). These results were also seen by Moser
and Hess (1968) who concluded that at least five inductive
cycles were needed to initiate the responses.

Similar short day treatments have been shown to
enhance tuberization in other tuberous plants. Weights of
tubers formed by 'Mc Cormack' potatoes under a 10 hour
photoperiod were 8 times greater than those formed under a

13 hour photoperiod (Garner and Allard, 1923). Three to

14

four weeks of an 8 1/2 hour phot0period applied from late
July increased the root weights in tuberous-rooted begonias
(Wasscher, 1955).

The effects of photOperiod conditions on the stages
of vegetative growth and flower formation and development in
several dahlia cultivars have also been reported. These
reports have greater implications regarding greenhouse
forcing.

During their tuberization experiments, Zimmerman and
Hitchcock (1929) also made observations on the flowering of
plants under different daylengths. They reported that both
cuttings and tuberous-rooted plants of 'Jersey's Beauty',
'Trentonian', 'Mrs I. de Ver Warner', and 'Insulinda'
flowered only with 7-9 hour photoperiods, and that a 16
photOperiod delayed flowering of 'John Erlich'.

During their tuberization experiment, Moser and Hess
(1968) found that vegetative growth was promoted by photo-
periods of 12 hours or longer. They concluded that photo-
period treatments regulated a competitive relationship
between vegetative growth and tuberization. They did not,
however, evaluate the flowering stage.

During a tuberization study (Yasuda and Yokoyama,
1959) with 'Hanagasa', the total number of flowers formed
from April 15 to September 1 was 446 for plants with a 13
hour photoperiod while the number of flowers decreased to

235 and 158 with 10 and 7 hour photoperiods, respectively.

15

The flowering response of tuberous-rooted plants of
4 dahlia types (Yasuda and Yokoyama, 1960) single, decora-
tive, cactus, and pompon was determined using an 8 hour
photoperiod, natural daylength (Japan-April to June) and
incandescent night lighting. After three weeks of treatment,
the 8 hour photoperiod produced the highest number of buds
recording 34, 22, 22, and 34 buds per the respective flower
types. Plants under the natural daylength had 32, 16, 12,
and 24 buds while night lighting reduced the number of buds
per plant to 20, 0, 0, and 25. Although the tuberous-roots
were planted on April 15, the controlled light conditions
were not initiated until June 1. Since floral bud initia-
tion has been shown to be completed within three weeks after
planting (Krijthe, 1938) and these treatments were started
6 weeks after planting, the effect of daylength would pri-
marily be on flower development.

The effects of phot0period on the tuberous-rooted
dahlias 'Broeder Justinus' and 'Finesse Anversoise' were
reported for continuous photoperiods of 10, 11, 12, 13, and
14 hours and natural daylength conditions from late May to
September 1 (Germany), (Maatsch and Rfinger, 1954). Plants
of 'Broeder Justinus' flowered earliest with the 12 hour
photoperiod while delays of 5, 15, and 22 days were seen
with 13 or 14 hour photoperiods or under the natural day-
length conditions. Plants of ‘Finesse Anversoise' flowered
earliest with the 11 hour phot0period and were delayed 7,

11, 25, and 35 days with 12, 13, or 14 hours or under the

16

natural day conditions. With the 11 hour photoperiod,
flowers of 'Finesse Anversoise' were abnormally formed, hav-
ing single rows of ray florets and 'Open-eye' centers.

For 'Broeder Justinus' the number of flowers at the
10, 11, 12, 13, and 14 hour and natural daylength treatments
was 0, 1.3, 6.3, 42.6, 28.9, and 19.1, while 'Finesse Anver-
soise' had 3.4, 10.7, 20.7, 55.4, 17.6 and 3.4 flowers.
They found maximum flower number with the 13 hour photoperiod
and reduction in flower numbers at treatments of 14 hours or
more. Flowering was severely affected by the 10 and 11 hour
photoperiods.

In 'Broeder Justinus' plant heights were 15, 25, 40,
55, and 50 cm for 8—11, 12, 13, and 14 hours and natural
daylength conditions, reSpectively. Shoot weights were 50,
100, 500, 1,400, and 1,800 g for 'Broeder Justinus' and 150,
300, 1,000, 1,500, and 2,200 g for 'Finesse Anversoise' with
11 or less, 12, 13, and 14 hour photOperiods and natural day
conditions. Vegetative growth was severely retarded with 11
hour or shorter phot0periods and increased with the longer
photoperiods. This is in agreement with the findings of
Moser and Hess (1968). The increase in plant weight at the
14 hour photoperiod or natural daylength conditions was
seen as an indicator of increased vegetative growth while
flowering was delayed and flower numbers were reduced. The
critical daylength of 12-13 hours was the most conducive

for flowering these cultivars.

17

In a study to determine the optimum daylength for
out flower production in Japan in autumn, the percent
flowering of cuttings of 'Akane' and 'Futurishizaka' was 0
and 35% with an 11 hour photOperiod, 20 and 57% with a 12
hour photoperiod, and 87 and 100% with a 13 hour photoperiod
(Konishi and Inaba, 1964). In the spring, the percent
flowering was 5, 70 and 100 for the 11, 12, and 13 hour
photoperiods with 'Akane'. Similarly, the fresh weights of
the vegetative shoots of these plants increased from 5 and
7 g at 11-12 hours to 45 and 20 g with a 13 hour photoperiod.
Lengths of stems were 5 and 15 cm at 11 and 12 hour photo-
periods, while at 13 hours the lengths were 83 and 78 cm for
the respective cultivars. The critical daylength was
determined to be 12 hours, with both vegetative and floral
growth suppressed by shorter photoperiods while longer
photoperiods enhanced both stages.

For cut flower production in England (Canham, 1969),
a two hour night break treatment with fluorescent lights
through January and February induced normal flower formation
10 and 8 weeks earlier than natural day plants of 'Newby'
and 'Chorus Girl' respectively. Flowers of plants grown
under natural daylengths were abnormally formed, having
'open-eye' centers and vegetative growth of the plants was
suppressed.

.Photoperiod treatments have also affected both the

dates of flowering and the flower number in Lilium longi-

 

florum. With an 18 hour photoperiod applied from the date

18

potting, flowering of 'Croft' lilies was 111 days, while
plants under a 9 hour photoperiod flowered in 119 days with
a constant temperature regime of 15.6°C (Smith and Langhans,
1962b). The number of flowers under the 18 hour photoperiod
was reduced, however, to 4.0, 3.4 and 2.0 at constant temper-
atures of 15.6, 18.3 and 21.1°C, while with a 9 hour photo-
period, plants averaged 4.5, 4.1 and 2.9 flowers.

The stem length of Lilium longiflorum has been

 

modified by the use of photoperiod treatments during the
forcing period (Kohl and Nelson, 1963, Smith and Langhans,
1962b, Wilkins, Waters, Widmer, 1968). With a 9 hour
phot0period applied from potting, plant heights of 'Croft'
lilies averaged 32.2 cm while with an 18 hour phot0period,
heights increased to 67.5 cm (Smith and Langhans, 1962b).
Heights of 'Ace' lilies forced with an 8 hour photoperiod
were 60 cm while with a 16 hour photoperiod they were 84.8
cm (Kohl and Nelson, 1963). The increased heights at
flowering were a result of increased internodal length.

During outdoor winter forcing of Gladiolus 'Sans

 

Souci' (Shillo and Halevy, 1976b) plants under the natural
daylength (10-12 hours) flowered in 123 days while flowering
of plants receiving 10-19 foot candles under either an 18
hour photoperiod or a 4 hour night break treatment was
delayed by 4 days. With these respective treatments, stalk
lengths were 155.1, 161.9 and 162.8 cm. Shortening the
natural daylength during summer forcing (13 1/2-14 1/2 hours)

to a 6 hour photOperiod reduced the flowering by 68%.

19

Also during summer forcing, 82, 71, 57, and 22% of 'Dr.
Fleming' flowered with natural day (ll-13 hours), 8 hour,

6 hour, and 4 hour phot0periods, respectively.

Growth Regulators

 

Exogenous applications of growth regulators on
dahlias have been used primarily to investigate their effects
on the rooting of cuttings or on the tuberization process.

Applications of indolebutyric acid alone (Biran and
Halevy, 1973c) or in combination with abscissic acid (Biran
and Halevy, 1973b) have increased the average number of roots
per cutting. The number of tuberous-roots, root diameters,
and root fresh weights were increased by daminozide and
chlormequat (Read, Dunham, Fieldhouse, 1972) and tuberiza-
tion was promoted by abscissic acid (Biran, Gur, Halevy,
1972) while GA3 (Moser and Hess, 1968) and ethephon (Biran,
Gur, and Halevy, 1972) suppressed tuberization.

Ancymidol, daminozide, and chlormequat are widely
used to regulate plant height on many greenhouse crops such

as Chrysanthemum morifolium, Euphorbia pulcherrima, and

 

Lilium longiflorum (Gortzig, 1974). Soil drench applications
have had longer-lasting effects than foliar sprays (Cathey
and Heggestad, 1973). However, resPonses have been modified
by cultivar sensitivity, growing conditions, dose rates,
stages of plant development, and time of application.
Recently, De Hertogh, Blakely, and Szlachetka (1976)

reported on the effectiveness of growth regulators on

20

controlling the height of forced tuberous-rooted dahlias.
For spring forcing of 'Park Princess', soil drenches of
ancymidol at the 0.5 mg rate per pot reduced plant heights
to 31.2 or 28.8 cm for 8 February or 9 March planting dates,
respectively, while heights of untreated plants were 46.0 cm.
Soil drenches of chlormequat at 270 or 540 mg per pot and
foliar sprays of daminozide at the 2,500 or 5,000 ppm rate
per plant were not effective. Soil drenches of ancymidol at
the 0.5 mg rate reduced plant heights of 'Kolchelsee' to
27.4 cm at the 8 February planting date while heights of
untreated plants, chlormequat-treated (270 mg, soil drench)
and daminozide-treated (2,500 ppm foliar spray) were 30.8,
34.4, and 41.5 cm, respectively. Application made two weeks
after the planting dates were more effective than those made
4 weeks after planting. Flower diameter and the number of
shoots per plant were not affected while flowering was
delayed by ancymidol in 'Kolchelsee' at the early planting

date but not.at the later date.

MATERIALS AND METHODS

Tuberous-roots were used and they were grown in the
Netherlands. They were harvested in October 1974 and 1975,
stored at 9 to 11°C, graded as size number II, washed just
prior to shipping, and then packed in cardboard cartons with
airdried peat to prevent drying. They were shipped on
December 23 and 17 in 1974 and 1975, respectively. They
arrived in East Lansing on January 13, 1975 and January 9,
1976. On arrival, the tuberous-roots were stored in the
shipping containers at 5°C until the dates of planting.
Prior to planting, shoot and root development was minimal.
Two cultivars had been selected for evaluation in all experi-
ments. 'Kolchelsee', a red semi-decorative type had rather
large tuberous-roots with four to five elongated storage
organs eight to ten cm long. 'Park Princess' a pink semi-
cactus flowered cultivar, had four to five spherical storage
organs which were three to four cm long.

In 1975, the tuberous-roots, washed free of packing
material, were dipped for thirty minutes in a solution con-
taining 44.8 g each of benomyl (50% WP) and ethazol (50% WP)
per 90 liters of water prior to planting. This pre-plant

dip was eliminated in 1976.

21

22

The tuberous-roots were planted one per 15 cm clay
pot with the crown region approximately one to two cm above
the level of the planting medium (Figure 1). The medium
consisted of sterilized soil, sand, peat, and Perlite (equal
volumes). The saturated soil extract test (Rieke and
Warncke, 1975) gave a soluble salts conductivity reading of

150 MHOS x 10'5

or 1050 ppm and a pH of 6.7.

Except in the fertilization experiments, Osmocote
(14-14-14) was incorporated into the planting medium at the
rate of 169.8 g per cubic foot, in 1975. In 1976, Osmocote
(14-14-14) was top dressed at the rate of 9 g per pot one
week after planting.

Two weeks after planting ancymidol was applied as a
soil drench to all plants at the rate of 0.5 mg per 15 cm
pot in 100 m1 of solution.

In all of the experiments, each treatment consisted
of five pots in three blocks. Pots were placed on the
benches in blocks which were designed to minimize the effects
of the peripheral heat source. Initially, spacing was pot
to pot and this later was increased to 35 cm centers when
shoot growth dictated it. All pots were thoroughly watered
immediately after planting and were subsequently watered as

needed to maintain adequate moisture. Treatments in the

individual experiments are described in the following pages.

Figure l.

A.
B.
C.

D.

23

A tuberous-root of 'Kolchelsee' planted
15 cm pot.

Old Stem
New Shoots
An Individual Enlarged Tuberous-Root

Fibrous Roots

in the

an

25

Fertilizer Experiments

 

In 1975, seven fertilization formulations were
evaluated (Tables 6 and 7). All tuberous-roots were planted
on 4 February. In 1976, only four fertilization formulations
were evaluated (Tables 8 and 9) and a February 6 planting
date was used.

All plants received natural daylength and full sun-
light conditions with a minimum night temperature of 17°C.
The specific fertilizer treatments were as follows:

1. No fertilizer was incorporated into the planting
medium prior to planting and no fertilizer was sub-
sequently applied.

2. Osmocote (14-14-14), a 3-4 month formulation was
incorporated into the planting medium prior to
planting at the rate of 169.8 g per cubic foot of
medium.

3. (1975) Osmocote (18-9-13), a 3-4 month formulation
was incorporated into the planting medium prior to
planting at the rate of 169.8 g per cubic foot.
(1976) Osmocote (14-14-14) was top dressed one week
after planting at the rate of 9 g per pot.

4. Osmocote (18-6-12), an 8-9 month formulation was
incorporated into the planting medium prior to plan-

ting at the rate of 169.8 g per cubic foot.

26

5. Osmocote (18-6-12) and Osmocote (14-14-14) were both
incorporated into the planting medium prior to plan-
ting at the rate of 84.9 g each per cubic foot of
medium.

6. Osmocote (18-9-13) and Osmocote (18-6-12) were both
incorporated into the planting medium prior to plant-
ing at the rate of 84.9 g each per cubic foot.

7. (1975) No fertilizer was incorporated into the plant-
ing medium. Plants received 200 ppm (20-20-20) in
300 m1 of solution per pot weekly.

Treatments 1 and 2 were the same in 1975 and 1976.
Treatment 7 in 1975 was treatment 4 in 1976. The other

treatments were not repeated.

Temperature Experiments

In 1975, (Tables 10 and 11) three maximum day/mini-
mum night temperature treatments were evaluated using two
planting dates, January 30 and February 20. In 1976, (Tables
1, 12 and 13) a fourth temperature treatment was included.
The planting dates remained the same. All plants received

natural daylength and full sunlight intensity.

Light Intensity Experiments
In 1975 and 1976 light intensity treatments giving
100, 75, and 50% of natural daylight were evaluated. Plas-

tic mesh was used to reduce the light intensity. Two

27

planting dates, January 30 and February 20 were used. Foot
candle measurements (Table 2) were determined with a direct
reading GE Type 213 light meter.

Table l.--Mean day/night temperatures during the 1976
forcing period.

 

 

 

Month °C

February 25/11 23/16 28/16 29/20
March 26/14 25/15 26/16 29/22
April 28/12 28/16 30/17 28/22
May 27/13 32/17 32/17 28/22
Seasonal Average 27/12 27/16 29/17 29/22

 

Table 2.--Foot candle measurements of the three light
intensity levels under different weather condi-
tions and dates, 1976.

 

DATE, CONDITION AND % LIGHT INTENSITY

 

 

TIME or READING 100 73 50
February 2 Clear AM 5000 3500 2500
February 5 Overcast AM 2000 1500 650-600
February 19 Clear AM 4000 3200 2000
February 26 Rainy AM 260 220 150
March 11 Clear AM 5000+ 5000+ 4000
March 17 Overcast PM 1500 1000 500-400
March 23 Partly Cloudy AM 2700 1800 1000-700
April 5 Cloudy PM 1500 1000 600-500

April 18 Clear PM 5000+ 4000+ 4000+

 

28

Table 3.--Solar radiation in calories/cmz/day at East
Lansing, Michigan.

 

 

WEEK MEAN RADIATION
01/31-02/06 191.1
02/21-02/27 251.8
03/08-03/14 292.4
03/15-03/21 326.0
04/05-04/11 378.0
04/26-05/02 423.6
05/10-05/16 465.1

 

a(Baker and Klink, 1975).

Table 4.--Calories/ cmz/day determinations under three
weather conditions at East Lansing, Michigan.

 

 

Month clotgozover clougogover cloudotclear)
January 50 150 215
February 100 250 380
March 120 380 480
April 150 480 500
May 200 550 700

 

a(Baker and Klink, 1975)..

Photoperiod Experiments
In 1975, four photOperiod treatments (Tables 18 and
19) were evaluated using two planting dates, January 30 and

February 20.

29

In 1976, four combination treatments were included
(Tables 20 and 21), and only one planting date, February 9
was used. These treatments evaluated long day and night-
break regimes with natural daylengths. Transfers from the
initial photOperiod to the finishing photoperiod took place
on March 15, five weeks after planting. The minimum night
temperature was 17°C. The specific photoperiod treatments
were as follows:

1. The natural daylength treatment received sunlight
available in a greenhouse at 42° 42' N. latitude.
The daylength varied from 10 to 14 hours by the
termination of the experiment (Table 5).

2. The 8 hour photOperiod treatment had black cloth
applied daily from 1630 to 0830 hours until termina-
tion of the experiment.

3. The 16 hour photOperiod, an extended day treatment,
was supplied by four cool-white 110 fluorescent
tubes suspended 92-102 cm above the bench surface
with 150-200 foot candles supplied to supplement the
natural daylength (Table 5). At the time of flower-
ing, the lights were approximately 60 cm above the
plants.

4. The four hour night break treatment was provided
using eight 60 watt incandescent bulbs with reflec-
tors suspended 56 cm apart and 92 cm above the bench.

Lights supplied 60-100 foot candles nightly between

30

2200 and 0200 hours. At the time of flowering,
lights were approximately 60 cm above the plants.
Table 5.--Number of daylight hours and times of photOperiod treatments

for dates during the 1976 forcing season at East Lansing,
Michigan, 43° north latitude.

 

 

Number Natural Black 16 Hour 4 Hour
Date of Daylight Daylengtha cloth lights lights
hours EST applied applied from applied
February 1 10.0 0750-1750 1630-0830 0200 hr. 2200-0200
February 9 10.5 0745-1800 " 0200 hr. "
February 20 11.25 0730-1815 " 0230 hr. "
March 6 11.5 0700-1830 " 0230 hr. "
March 12 11.5 0700-1830 " 0230 hr. "
March 26 12.5 0630-1900 " 0300 hr. "
April 15 13.5 0600-1930 " 0330 hr. "
April 30 14.0 0630-2000 " 0430 hr. "
May 1 14.2 0630-2040 " 0430 hr. "
May 11 14.7 0615-2100 " 0500 hr. "

 

aDaylight savings time went into effect on April 30 and
continued throughout the experiment.

Hydrogel Experiment

 

In 1975, three rates of the soil amendment hydrogel
(Viterra) were evaluated (Tables 22 and 23). The tuberous-
roots were planted on February 4. Plants received natural
daylength with full sunlight intensity and the minimum night
temperature was 17°C. Specific treatments were applied as

follows:

31

1. No hydrogel was incorporated.

2. Hydrogel at the rate of 339.6 g per cubic foot was
incorporated into the planting medium prior to
planting.

3. Hydrogel at the rate of 226.4 g per cubic foot of
planting medium was incorporated prior to planting.

Pots were thoroughly watered immediately after planting and
were subsequently watered as needed to maintain adequate
moisture levels. These requirements varied with the rate of

hydrogel incorporated.

Pesticide Usage

 

In 1975, plants in all experiments received a soil
drench of ethazol at the rate of 22.2 g per 45 liters of
water with 200 m1 of solution applied per pot on March 17.
Plants were sprayed with 'Malathion' to runoff on March 18.
Aldicarb was applied to the soil surface at the rate of 0.1
g per pot, worked and watered in on March 20.

In 1976, Aldicarb was applied at the same rate and
in the same manner on March 19.

In 1975, many plants of 'Kolchelsee' regardless of
the treatment or soil moisture level became wilted. To
aerate the planting medium, plants were removed from the
pots and the root clumps were given a quarter turn before
being replaced into the pots on March 26. A11 pots were
then heavily leached weekly and allowed to drain. Soil

samples from wilted plants were tested and the results

32

indicated that the main cause of the wilting was high solu-
ble salts and overwatering. The soft rot bacteria Pectobac-
terium g2, was reported as present in root tissue, although

it was not a causal agent of wilting.

Removal of Failures

 

For all treatments, tuberous-roots which did not
produce shoots 4-6 weeks after planting were removed. These

losses were low, from 3 to 5%.

Data Collection

 

For all experiments, specific parameters were mea-
sured as indices of the plant response to the treatments.

The number of days to flower for the first, second,
and third flowers per plant was determined from each plant-
ing date to the date when the flower was fully opened.

The promotion or delay of flowering was determined
by comparing the mean number of days when 100% of the plants
in a treatment had flowered. In some treatments of the
fertilizer and photoperiod experiments some of the plants
failed to flower. Therefore, the mean of the maximum
percent which did flower was determined and compared.

The height of the flower stalks of the first, second,
and third flowers was measured from the crown of the
tuberous-root to the base of the fully Open flower head.

The longevity (flower life) of the first, second,
and third flowers per plant was determined by recording the

number of days from flower opening to the senescence.

33

The diameter of the first, second, and third flowers
per plant was measured from the distal ends of the florets
through the center of the flower on the day each flower was
fully opened.

The number of major and minor shoots which arose
from the crown of the tuberous-root was also recorded. The
major shoots were the vigorous shoots which flowered earli-
est while the minor shoots were those less vigorous and
delayed in flowering. The total number of shoots which
arose from the crown was determined by summing the values

obtained for both types of shoots.

Statistical Analysis

 

The experiments were conducted as randomized com-
plete block designs with 2 x 2 factorial analyses conducted
on the data.

Means in rows were compared using the Tukey omega-
procedure to determine the treatment significance on each
parameter, for each planting date, and for each cultivar.
Means in columns were separated by the omega-procedure for
each parameter, for each cultivar at one treatment level to
determine the significance of the planting dates (Steele
and Torrie, 1960).

In determining the treatment effects on the forcing
parameters, it is important to note the limitations under
which the experiments were conducted. The error variance

in the experiments is likely to be overestimated if the

34

effects of the blocks interacted with those of the treatments
or planting dates. Thus, the tests of significance of the
treatment levels and planting dates were conservative.
Although the level of significance may have been inexactly
determined, the large differences were primarily caused by
the treatment levels, cultivars, and planting dates with

consistent responses seen for the two years of data.

RESULTS AND DISCUSS ION

Forcing,Criteria

The forcing of dahlias as a commercial greenhouse

crop depends upon the use of environmental factors which

will produce high quality plants. The specific criteria for

dahlias satisfactory as pot plants include the following:

1.
2.

Forcing time should not exceed 84 days.

Ninety-five percent of the plants should flower
within a 10 day period.

Plant height from the crown to the base of the first
fully opened flower should range from 30—40 cm when
planted in a 15 cm pot.

Flower diameters should range from 10 to 15 cm when
fully opened.

Plants should have 2-4 flowers open at the same time
and there should be 10 or more floral buds initiated
and developed.

Plants should have dense and well-formed foliage with
an attractive color.

Plants should have an indoor keeping quality of 2-4
weeks, with good transplanting characteristics and

continued flowering.

35

36

These criteria were used as guidelines to judge satisfactory
plant quality in the following discussion of the experimen-
tal results and an example of a high quality plant is

illustrated in Figure 2.

Effects of Fertilization

In both years, fertilizer treatments markedly
affected plant growth characteristics (Tables 6, 7, 8 and 9).
With 'Kolchelsee', the fertilizer treatments increased the
percent of plants flowering from 0 to 100% in 1975, and from
53, 26, and 0% for the first, second, and third flowers,
respectively, to 100% in 1976. With 'Park Princess', ferti-
lizer treatments also increased the percent flowering of
first, second, and third flowers from 73, 40, and 30% to
100% in 1975, while in 1976 it increased from 33 and 0% for
second and third flowers to 100%. The higher percent
flowering of both cultivars without fertilization from 1975
to 1976 reflects year to year variation during production
and forcing periods.

On the average, applications of fertilizer promoted
earlier flowering by 20 days. Plant heights, flower diame-
ters and flower longevity, and the total number of shoots
and flowers per plant were also increased. Thus, fertiliza-
tion is essential in the production of high quality plants
forced from tuberous-roots.

In both years, there were differences in some of the

forcing parameters among the fertilizer treatments. But the

37

Figure 2. A high quality plant of 'Park Princess'
after forcing.

38

 

39

Table 6.--Effect of fertilizer treatments on the number of days to flower, plant
height, flower longevity, and diameter of the first three flowers and
number of shoots produced per plant of 'Kolchelsee'. Tuberous-roots
were planted on 4 February, 1975.

 

. X
PLANT ORGAN FERTILIZER TREATMENTS

EVALUATED Noney 14-14-14 18-9-13 18-6-12 18-6-12 18-9-13 20-20-20
14-14-14 18-6-12 Liquid

 

Days to Flower

First Flower - 65a 70b 72b 70b 72b 70b
Second Flower - 77a 78a 82ab 81ab 80ab 84b
Third Flower - 86a 85a 86a 90ab 87ab 92b

Plant Height (cm)

First Flower - 26.1bc 25.3abc 29.0c 22.2a 26.5bc 23.6ab
Second Flower - 31.4a 29.5ab 36.9c 28.2ab 31.1a 26.2b
Third Flower - 34.1cb 31.4c 38.9a 31.9c 36.1ab 27.9d

Flower Longevity (Days)

First Flower - 7.4a 7.2a 7.3a 7.2a 6.2b 6.7ab
Second Flower - 6.5a 7.3a 6.8a 6.7a 7.0a 6.9a
Third Flower - 6.9bc 6.9bc 7.6c 5.9a 6.3ab 6.8bc

Diameter (cm)

First Flower - 5.8a 5.8a 6.3b 5.9ab 6.0ab 5.9ab
Second Flower - 5.7a 5.7a 5.8a 5.9a 5.8a 5.5a
Third Flower — 5.5a 5.8a 5.6a 5.8a 5.7a 5.3a

Number of Shoots Per Plant

Major Shoots 1.0a 1.8bc 2.0b 1.1a 1.5c 1.5c 1.1a
Minor Shoots 0.3a 0.9b 0.6ab 0.5ab 0.3a 0.5ab 0.5ab
Total Shoots 1.3a 2.7b 2.6b 1.6ac 1.8c 2.0c 1.6ac

 

xMeans followed by the same letter (a,b,c,d) are not significantly different
by Tukey's test at .05 for single rows (each organ per parameter determined
separately).

yNone of the plants flowered.

4()

Table 7.--Effect of fertilizer treatments on the number of days to flower, plant
height, flower longevity, and diameter of the first three flowers and
number of shoots produced per plant of 'Park Princess'. Tuberous-
roots were planted on 4 February, 1975.

 

X
PLANT ORGAN FERTILIZER TREATMENTS

EVALUATED Noney 14-14-14 18-9-13 18-6-12 18-6-12 18-9-13 20-20-20
14-14-14 18-6-12 Liquid

 

Days to Flower

First Flower 88(73%)a 72b 74bc 76c 75bc 74bc 75bc
Second Flower 98(40%)a 78b 79bc 82bc 82bc 78b 84c
Third Flower 105(30%)a 82b 83b 89cd 86bc 85bc 93d

Plant Height (cm)

First Flower 23.9(73%)a 28.8bc 34.3d 31.8cd 29.9bc 29.8bc 26.4ab
Second Flower 29.5(40%)a 32.6ab 35.9b 35.2b 30.4a 30.6a 30.8a
Third Flower 30.7(30%)a 34.8bc 37.9b 37.5b 35.3bc 34.9bc 32.7ac

Flower Longevity (Days)

First Flower 6.8(73%)a 7.5ab 7.5ab 7.6ab 7.8b 7.7b 8.3b
Second Flower 6.9(40%)a 6.9a 8.1b 6.5a 6.9a 8.1b 7.0ab
Third Flower 6.3(30%)ac 7.0ab 7.3b 6.8ab 6.5abc 6.3ac 5.8c

Diameter (cm)

First Flower 11.0(73%)a 12.0b 11.9b 12.3b 12.2b 12.3b 12.2b
Second Flower 9.7(40%)a 11.7b 12.0bc 11.9bc 12.1c 11.7b 11.6b
Third Flower 7.3(30%)a 11.8b 11.6b 11.8b 11.6b 11.7b 10.8c

Number of Shoots Per Plant

Major Shoots 1.4a 2.2bc 2.0bc 1.8b 2.2bc 2.4c 1.9b
Minor Shoots 1.0ab 1.4b 1.3ab 0.8a 1.2ab 0.9a 1.1ab
Total Shoots 2.4a 3.6c 3.3bc 2.6a 3.4c 3.3bc 3.0b

 

xMeans followed by the same letter (a,b,c,d) are not significantly different
by Tukey's test at .05 for single rows (each organ per parameter determined
separately).

YMaximum percent of plants flowering is given.

41.

Table 8.--Effect of fertilizer treatments on the number of days to flower, plant
height, flower longevity, and diameter of the first three flowers and
number of shoots produced per plant of 'Kolchelsee'. Tuberous-roots
were planted on 6 February, 1976.

 

 

x

PLANT ORGAN FERTILIZER TREATMENTS

EVALUATED Noney 14-14-14 14-14-14 20-20-20
Incorporated Top dressed Liquid

 

Days to Flower

First Flower 84(53%)a 65b 69bc 74c
Second Flower 109(26%)a 71b 76b 77b
Third Flower — (0%) 80a 77a 81a

Plant Height (cm)

First Flower 27.1(53%)a 30.8a 31.8a 38.9a
Second Flower 30.3(26%)a 34.2a 35.6a 41.4a
Third Flower - (0%) 38.9a 41.4a 44.5a

Flower Longevityg(Days)

First Flower 7.7(53%)a 6.0b 5.9b 5.9b
Second Flower 8.0(26%)a 5.8b 7.2ab 5.8b
Third Flower — (0%) 7.3a 7.3a 6.6a

Diameter (cm)

First Flower 5.5(53%)a 6.1a 5.8a 5.9a
Second Flower 4.3(26%)a 5.5b 5.8b 5.8b
Third Flower - (0%) 5.6a 5.6a 5.6a

Number of Shoots Per Plant

Major Shoots 1.0a 1.5a 1.5a 1.8a
Minor Shoots 0.4a 1.0a 0.9a 0.9a
Total Shoots 1.4a 2.5b 2.4b 2.7b

Number of Flowers and Buds Per Plant

Total Flowers
and Buds 1.3a 8.5b 8.2b 8.7b

 

xMeans followed by the same letter (a,b,c) are not significantly different
by Tukey's test at .05 for single rows (each organ per parameter determined
separately).

yMaximum percent of the plants flowering is given.

‘42

Table 9.--Effect of fertilizer treatments on the number of days to flower, plant
height, flower longevity, and diameter of the first three flowers and
number of shoots produced per plant of 'Park Princess'. Tuberous-roots
were planted on 6 February, 1976.

 

X
PLANT ORGAN FERTILIZER TREATMENTS

EVALUATED Noney 14-14-14 14-14-14 20-20-20
Incorporated Top dressed Liquid

 

Days to Flower

First Flower 90a 73b 74b 76b
Second Flower 98(33%)a 74b 77b 80b
Third Flower -(0%) 81a 81a 86a

Plant Height (cm)

First Flower 32a 41a 45a 38a
Second Flower 35(33%)a 43a 46a 42a
Third Flower -(0%) 44a 48a 43a

Flower Longevity (Days)

First Flower 9.0a 8.4a 9.0a 8.1a
Second Flower 8.8(33%)a 8.4a 7.7a 8.0a
Third Flower -(0%) 8.1a 7.7a 8.1a

Diameter (cm)

First Flower 10.3a 12.1b 12.2b 12.4b
Second Flower 8.3(33%)a 11.4b 11.6b 11.6b
Third Flower -(O%) 11.7a 11.9a 11.3a

Number of Shoots Per Plant

Major Shoots 1.2a 1.8a 1.9a 1.4a
Minor Shoots 0.4a 0.4a 0.7a 0.7a
Total Shoots 1.6a 2.2b 2.6b 2.1b

Number of Flowers and Buds Per Plant

Total Flowers

 

xMeans followed by the same letter (a,b,c) are not significantly different

by Tukey's test at .05 for single rows (each organ per parameter determined
separately).

YMaximum percent of the plants flowering is given.

43

data indicated that balanced formulations of Osmocote (14-
14-14) or soluble fertilizers (20-20-20) were satisfactory.
Also, the higher nitrogen formulations, (18-6-12) or (18-9-
13), did not delay flowering and are not required.

These results are consistent with recommendations
that dahlias should be fertilized when grown in the garden
(James, 1963, Vance, 1974, Baumgardt, 1970). There have
been no previous studies on fertilizer requirements for
greenhouse forced tuberous-rooted dahlias. De Hertogh,
Blakely, and Szlachetka (1976) used 30 ppm liquid feed appli-
cations in their study on the effects of growth regulators
on forced tuberous-rooted dahlias and this would appear to
be on the low side.

In its basic responses to fertilizer treatments, the

dahlia is similar to Lilium and Gladiolus in their levels of

 

fertilizer recommended during forcing (Kiplinger and
Langhans, 1967, Kosugi, 1960). It differs greatly, however,

from the bulbous materials such as Tulipa, Hyacinthus, and

 

 

Narcissus which do not normally require fertilization during

forcing (De Hertogh, 1973).

Effects Of Temperature

 

In 1975, (Tables 10 and 11), flowering was promoted
with an increase in the day/night temperatures from 26/11 to
23/16 and 27/18°C from 103 to 84 and 64 days and from 93 to
74 and 68 days for 'Kolchelsee' and 'Park Princess' respec-

tively. Comparing planting dates, flowering was accelerated

44

Table 10.--Effect of temperature on the number of days to flower, plant
height, flower longevity, and diameter of the first three
flowers and number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were planted in 1975.

 

 

 

 

 

PLANT ORGAN PLANTING DAY/NIGHT TEMPERATURES °cx
EVALUATED DATE 26/11 23/16 27/18
Days to Flower
First Flower 30 Jan 103a/d 84b/d 63c/d
20 Feb 91a/e 62b/e 59b/d
Second Flower 30 Jan llla/d 99b/d 7lc/d
20 Feb 98a/e 69b/e 64b/d
Third Flower 30 Jan 116a/d 104b/d 74c/d
20 Feb 97a/e 73b/e 67b/e
Plant Height (cm)
First Flower 30 Jan 35.7a/d 24.9b/d 31.1ab/d
20 Feb 38.0a/d 21.7b/d 32.4a/d
Second Flower 30 Jan 40.7a/d 30.4b/d 35.7ab/d
20 Feb 41.9a/d 26.2b/d 38.4b/d
Third Flower 30 Jan 41.2a/d 35.2a/d 37.4a/d
20 Feb 46.8a/d 28.4b/d 41.3a/d
Flower Longevityi(Days)
First Flower 30 Jan 5.9a/d 6.9a/d 7.2b/d
20 Feb 5.2a/d 6.9a/d 7.0b/d
Second Flower 30 Jan 5.2a/d 5.7a/d 7.3b/d
20 Feb 5.7a/d 7.3b/e 7.2b/d
Third Flower 30 Jan 6.9a/d 7.0a/d 7.3a/d
20 Feb 5.3a/d 7.0a/d 6.9a/d

 

Table 10.--Continued.

45

 

 

 

 

 

PLANT ORGAN PLANTING DAYZNIGHT TEMPERATURES °Cx

EVALUATED DATE 26/11 23/16 27/18
Diameter (cm)

First Flower 30 Jan 5.4a/d 5.8a/d 5.8a/d
20 Feb 5.9a/d 6.3a/d 6.2a/d
Second Flower 30 Jan 5.8a/d 5.5a/d 5.7a/d
20 Feb 6.1a/d 6.0a/d 5.9a/d
Third Flower 30 Jan 5.5a/d 5.7a/d 5.6a/d
20 Feb 5.5a/d 5.9a/d 5.9a/d

Number of Shoots Per Plant
Major Shoots 30 Jan 1.7a/d 1.5a/d 1.7a/d
20 Feb 1.4a/d 1.5a/d 1.6a/d
Minor Shoots 30 Jan 0.6a/d 0.6a/d 0.3a/d
20 Feb 0.4a/d 0.5a/d 0.4a/d
Total Shoots 30 Jan 2.3a/d 2.1a/d 2.0a/d
20 Feb 1.8a/d 2.0a/d 2.0a/d

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows
(each organ per date and parameter determined separately). Means
followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each
organ per treatment and parameter determined separately).

46

Table ll.--Effect of temperature on the number of days to flower, plant
height, flower longevity, and diameter of the first three
flowers and number of shoots produced per plant of 'Park
Princess'. Tuberous-roots were planted in 1975.

 

 

 

 

PLANT ORGAN PLANTING DAY/NIGHT TEMPERATURES °cx
EVALUATED DATE 26/11 23/16 27/18
Days to Flower
First Flower 30 Jan 93a/d 74b/d 68b/d
20 Feb 89a/d 67b/d 63b/d
Second Flower 30 Jan lOOa/d 79b/d 73b/d
20 Feb 94a/d 74b/d 69b/d
Third Flower 30 Jan lOSa/d 85b/d 77b/d
20 Feb 97a/e 78b/e 72b/d
Plant Height (cm)
First Flower 30 Jan 36.4a/d 32.3a/d 35.1a/d
20 Feb 34.9a/d 30.1a/d 27.1a/e
Second Flower 30 Jan 38.7a/d 32.1b/d 36.9ab/d
20 Feb 37.7a/d 37.1a/d 31.9a/d
Third Flower 30 Jan 39.0a/d 45.5a/d 38.5a/d
20 Feb 39.6a/d 38.1a/d 34.8a/d
Flower Longevity (Days)
First Flower 30 Jan 6.5a/d 7.9a/d 9.9b/d
20 Feb 7.5a/d 7.8a/d 6.8a/e
Second Flower 30 Jan 7.1a/d 7.7a/d 8.9a/d
20 Feb 7.9a/d 7.7a/d 6.9a/e
Third Flower 30 Jan 7.0ab/d 6.2a/d 8.3b/d
20 Feb 9.9a/e 8.3a/e 8.0a/d

 

 

Table ll.--Continued.

47

 

 

 

 

 

PLANT ORGAN PLANTING DAT/NIGHT TEMPERATURES °cx
EVALUATED DATE 26/11 23/16 27/18
Diameter (cm)
First Flower 30 Jan 12.3a/d 12.4a/d 11.2b/d
20 Feb 13.2a/e 12.4a/d 12.7a/e
Second Flower 30 Jan 11.0a/d 12.1b/d 11.2ab/d
20 Feb 11.8a/d 11.6a/d 11.4a/d
Third Flower 30 Jan 11.4a/d 12.2a/d 11.5a/d
20 Feb 11.2a/d 11.4a/d 11.6a/d
Number of Shoots Per Plant
Major Shoots 30 Jan 1.7a/d 2.3a/d 1.9a/d
20 Feb 1.6a/d 1.5ab/e 2.2a/d
Minor Shoots 30 Jan 1.4a/d 1.0a/d 1.6a/d
20 Feb 1.2a/d 0.7a/d 0.4a/e
Total Shoots 30 Jan 3.1a/d 3.3a/d 3.5a/d
20 Feb 2.8a/d 2.2a/d 2.6a/d

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows

(each organ per date and parameter determined separately).

Means

followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each

organ per treatment and parameter determined separately).

48

for all temperatures with the second planting. The range
was from 4 to 31 days. The cultivars differed with 'Park
Princess' flowering 2-11 days earlier than 'Kolchelsee'
under comparable treatments.

At 26/11°C, plant heights were significantly
increased, averaging 40 and 37 cm for 'Kolchelsee' and
'Park Princess' while heights at 23/16°C averaged 28 and 36
cm and at 27/18°C heights were 35 and 34 cm for the respec-
tive cultivars. Flower longevity, flower diameter, and the
number of shoots per plant were not affected by temperature
or planting date.

Since the upper temperature limit for forcing was
not established in 1975, an additional day/night temperature
treatment was included in the 1976 study. Again, the data
showed that flowering was promoted by increasing temperatures
(Tables 12 and 13). The higher temperature permitted the
earliest initiation and floral develOpment but adverse
affects on overall plant quality were noted.

Cultivars again differed in their response. 'Kol-
chelsee' flowered a maximum of 16 days earlier than 'Park
Princess'. Year to year variation was reflected by the
average promotion of flowering by 6 days from 1975 to 1976
for comparable treatments.

The 29/22°C treatments produced the earliest flow-
ering with both cultivars. With the 29/17°C treatments

flowering was delayed to 62 and 64 days for 'Kolchelsee'

49

Table 12.--Effect of temperature on the number of days to flower, plant
height, flower longevity, and diameter of the first three
flowers and number of Shoots produced per plant of
'Kolchelsee'.

Tuberous-roots were planted in 1976.

 

 

 

 

 

 

PLANT ORGAN PLANTING DAY/NIGHT TEMPERATURES °cx
EVALUATED DATE 27/12 27/16 29/17 29/22
Days to Flower

First Flower 30 Jan 81a/d 71b/d 59c/d 55c/d
20 Feb 84a/d 75b/d 57c/d S4c/d

Second Flower 30 Jan 88a/d 76b/d 63c/d 62c/d
20 Feb 9la/d 82a/d 61b/d 59b/d

Third Flower 30 Jan 94a/d 81b/d 67c/d 66c/d
20 Feb 96a/d 84b/d 66c/d 59c/d

Plant Height (cm)

First Flower 30 Jan 37.6a/d 31.6a/d 34.4a/d 19.5b/d
20 Feb 38.1a/d 30.7b/d 32.1ab/d 29.4b/e

Second Flower 30 Jan 42.0a/d 32.7b/d 38.7b/d 24.7c/d
20 Feb 47.3a/e 37.5bc/e 39.3b/d 31.5c/e

Third Flower 30 Jan 45.2a/d 35.6bc/d 40.7ab/d 29.5c/d
20 Feb 50.4a/d 37.5b/d 39.4b/d 36.7b/e

Flower Longevity (Days)

First Flower 30 Jan 5.8a/d 6.1a/d 6.5a/d 5.9a/d
20 Feb 6.9a/d 7.3a/d 6.2a/d 5.3a/d

Second Flower 30 Jan 7.9a/d 6.1b/d 6.5ab/d 5.7b/d
20 Feb 7.3a/d 7.3a/d 6.3ab/d 5.2b/d

Third Flower 30 Jan 8.2a/d 6.3ab/d 6.2ab/d 5.1b/d
20 Feb 7.8a/d 6.5ab/d 6.3ab/d 5.4b/d

Table 12.--Continued.

50

 

 

 

 

 

 

PLANT ORGAN PLANTING DAY/NIGHT TEMPERATURES °cx
EVALUATED DATE 27/12 27/16 29/17 29/22
Diameter (cm)

First Flower 30 Jan 6.0a/d 6.0a/d 6.3a/d 5.7a/d
20 Feb 6.3a/d 6.0a/d 6.0a/d 5.7a/d

Second Flower 30 Jan 5.7a/d 5.5a/d 6.2a/d 5.7a/d
20 Feb 6.2a/e 5.9a/d 5.7a/d 5.5a/d

Third Flower 30 Jan 5.7a/d 5.3a/d 5.9a/d 5.5a/d
20 Feb 5.7a/d 5.5a/d 5.7a/d 5.2a/d

Number of Shoots Per Plant

Major Shoots 30 Jan 1.5a/d 1.7a/d 1.5a/d 1.8a/d
20 Feb 1.3a/d 1.2a/e 1.4a/d 1.8a/d

Minor Shoots 30 Jan 0.9a/d 0.8a/d 0.5a/d 0.7a/d
20 Feb 0.7a/d 0.8a/d 0.7a/d 0.1a/d

TOtal Shoots 30 Jan 2.3a/d 2.5a/d 1.9a/d 2.5a/d
20 Feb 1.9a/d 2.0a/d 2.1a/d 1.9a/d

Number of Flowers and Buds Per Plant

Total Flowers

and Buds 30 Jan 9.4a/d 7.4ab/d 8.0ab/d 6.2b/d
20 Feb 7.3ab/d 5.7a/e 10.0b/e 8.1b/e

 

IMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows
(each organ per date and parameter determined separately).
followed by the same letter following the slash (d,e) are not signifi-

cantly different by Tukey's test at .05 for pairs in columns (each

organ per treatment and parameter determined separately).

51

Table l3.-Effect of temperature on the number of days to flower, plant
height, flower longevity, and diameter of the first three
flowers and number of shoots produced per plant of 'Park

Princess'.

Tuberous-roots were planted in 1976.

 

 

 

 

 

 

PLANT ORGAN PLANTING DAY/NIGHT TENTERATURES °Cx
EVALUATED DATE 27/12 27/16 29/17 29/22
Days to Flower

First Flower 30 Jan 87a/d 82a/d 61b/d 54b/d
20 Feb 88a/d 76b/d 60c/d 56c/d

Second Flower 30 Jan 93a/d 89a/d 64b/d 58b/d
20 Feb 94a/d 87a/d 66b/d 60b/d

Third Flower 30 Jan 96a/d 97a/d 67b/d 59b/d
20 Feb 96a/d 94a/d 69b/d 60b/d

Plant Height (cm)

First Flower 30 Jan 36.8a/d 28.9b/d 39.3a/d 21.4c/d
20 Feb 37.2a/d 27.0b/d 34.6a/d 21.8b/d

Second Flower 30 Jan 38.4a/d 31.6b/d 43.5a/d 29.2b/d
20 Feb 39.8a/d 30.1b/d 38.5a/e 25.2b/d

Third Flower 30 Jan 37.5a/d 35.2a/d 47.8b/d 30.2a/d
20 Feb 38.6a/d 29.3b/e 38.7a/e 28.3b/d

Flower Longevity (Days)

First Flower 30 Jan 8.9a/d 8.6ab/d 7.3ab/d 6.7b/d
20 Feb 9.1a/d 10.7a/e 8.7ab/d 6.9b/d

Second Flower 30 Jan 8.7a/d 9.1a/d 7.8ab/d 6.2b/d
20 Feb 8.7a/d 9.0a/d 8.7a/d 7.6a/e

Third Flower 30 Jan 7.5a/d 10.3b/d 7.4a/d 6.4a/d
20 Feb 7.2a/d 9.3b/d 9.2b/e 7.6abé

Table l3.--Continued.

52

 

 

 

PLANT ORGAN PLANTING DAY/NIGHT TEMPERATURES °Cx
EVALUATED DATE 27/12 27/16 29/17 29/22
Diameter (cm)
First Flower 30 Jan 11.8ab/d 12.2a/d 12.4a/d 11.2b/d
20 Feb 12.4a/e 13.0a/e 11.0b/e 10.6b/e
Second Flower 30 Jan 11.4a/d 12.6b/d 11.3a/d 10.4a/d
20 Feb 12.3a/e 11.3b/e 10.2c/e 9.9c/d
Third Flower 30 Jan 11.5ab/d 12.2a/d 10.9b/d 10.6b/d
20 Feb 11.7a/d 10.6b/e 10.1b/e 9.6b/e
Number of Shoots Per Plant
Major Shoots 30 Jan 1.3a/d 1.5ab/d 2.0ab/d 1.9ab/d
20 Feb 1.3a/d 1.4a/d 1.3a/e 1.6a/d
Minor Shoots 30 Jan 1.4a/d 0.6a/d 0.6a/d 0.6a/d
20 Feb 1.6a/d 0.8a/d 0.7a/d 0.7a/d
Total Shoots 30 Jan 2.7a/d 2.1a/d 2.6a/d 2.6a/d
20 Feb 2.9a/e 2.2a/d 1.9a/d 2.3a/d
Number of Flowers and Buds Per Plant
TOtal Flowers 30 Jan 6.6a/d 6.3a/d 10.5b/d 10.0b/d
and Buds 20 Feb 6.7a/d 3.3b/e 5.1ab/e 7.3a/e

 

 

 

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows

(each organ per date and parameter determined separately).

Means

followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each
organ per treatment and parameter determined separately).

53

and 'Park Princess', respectively due to the lower night
temperature since the day temperatures were approximately
equal.

The delaying effects of the lowered night tempera-
ture was demonstrated by the 27/16°C treatment in which
flowering averaged 78 and 86 days for 'Kolchelsee' and
'Park Princess', respectively. The greatest delay in
flowering occurred with the 27/12°C treatment. This showed
the retarding effect of the lowest minimum night temperature
since the average day temperature approximately equalled
that of two other treatments. Since there was no effect of
planting date, the minimum days to flower at each tempera-
ture was probably due to the higher day temperature.

Plant heights of 'Park Princess' at 27/16°C averaged
30.3 cm. This was significantly less than 39.2 cm at 27/
12°C or 34 cm at the 29/17°C treatment. Likewise, plant
heights of 'Kolchelsee' at 27/16°C averaged 34 cm and this
was significantly less than 43.4 cm at 27/12°C or 37 cm at
the 29/17°C treatments.

Flower diameters, flower longevity, and the number
of shoots, flowers and buds per plant were only minimally
affected by these temperatures or planting dates.

The 29/22°C treatment was suboptimal for forcing
both cultivars because of the adverse effects noted. The
flower diameters were decreased, plant heights and leaf
areas were reduced, and the foliage had a chlorotic con-

dition.

54

Since the dahlia, like the Easter lily and bulbous
Trig, does not have differentiated flower parts at planting
time, temperature treatments applied from the data of pot-
ting to flowering would affect the rates of differentiation,
development of floral organs and the rate of vegetative
growth. The promotion of flowering in the dahlia by
increasing day and/or night temperatures has been similarly
demonstrated with both the 'Ace' and 'Croft' Easter lilies

as well as with several cultivars of Iris hollandica. In

 

practice, temperatures could be temporarily raised or
lowered to either accelerate or delay crop development in
order to meet the market demand.

In dahlias, the best height control was produced
with the 27/16°C treatment. With the 29/17°C treatment,
plants were too tall to be acceptable. This response had
been similarly reported with 'Ace' lilies (Roh and Wilkins,
1973) and Trig 'Wedgewood' (Fortanier and Zevenbergen,
1973).

The increases in height of dahlias at flowering may
be due to more rapid vegetative growth at the higher day
and night temperatures prior to the application of ancymidol.
Thus, regardless of planting date, it appears that ancymidol
must be applied before shoots exceed 3 cm if good height

control is to be obtained.

55

Effects of Light Intensity

Light intensity treatments markedly affected the
height of plants of both cultivars in 1975 and 1976 (Tables
14, 15, 16, and 17). Plants grown under 50% of the natural
light intensity were 10 and 11 cm taller than those grown
under the 75 or 100% levels, respectively.

In both years, heights of 'Kolchelsee' of the second
planting date averaged 10 cm taller than those of the first
planting date. Heights of 'Park Princess' however, were not
significantly different with the two planting dates.

In 1975, the 50 and 75% light intensity treatments
promoted the opening of first flowers of 'Kolchelsee' by 13
and 10 days earlier than the 100% light intensity treatment
of the first planting date. However, in 1976, there were
no differences due to treatments or planting dates. The
50% light intensity treatment also delayed the opening of
first flowers of 'Park Princess' by 8 and 4 days at the
respective planting dates in 1975, but in 1976 delayed
opening by 5 days only of the first planting date.

With 'Park Princess' flower longevity was increased
under the 50% light intensity level in 1976. Also, in 1976,
longevity was increased of the second planting date for
both cultivars.

At the 50% level, 'Park Princess' had a reduced num-
ber of flowers and buds, but an increased number of shoots.

Flower diameter was unchanged by treatments.

56

Table l4.--Effect of light intensity on the number of days to flower,
plant height, flower longevity, and diameter of the first
three flowers and number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were planted in 1975.

 

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS %x
EVALUATED DATE 100 75 50
Days to Flower
First Flower 30 Jan 86a/d 76b/d 73b/d
20 Feb 68a/e 69a/e 64a/e
Second Flower 30 Jan 94a/d 89a/d 87a/d
20 Feb 75a/e 76a/e 73a/e
Third Flower 30 Jan lOla/d 97a/d 96a/d
20 Feb 78a/e 80a/e 78a/e
Plant Height (cm)
First Flower 30 Jan 28.9a/d 37.6a/d 37.8b/d
20 Feb 39.9a/e 43.3a/e 43.2a/d
Second Flower 30 Jan 36.9a/d 34.0a/d 51.5b/d
20 Feb 44.3a/e 48.5ab/e 52.7b/d
Third Flower 30 Jan 37.5a/d 39.2a/d 58.7b/d
20 Feb 46.5a/e 51.7ab/e 54.4b/d
Flower Longavity (Days)
First Flower 30 Jan 7.0a/d 6.7a/d 8.2a/d
20 Feb 7.4a/d 6.4a/d 7.0a/d
Second Flower 30 Jan 6.3a/d 6.8a/d 7.1a/d
20 Feb 7.0a/d 6.9a/d 7.6a/d
Third Flower 30 Jan 6.3a/d 7.1a/d 7.4a/d
20 Feb 6.8a/d 7.0a/d 7.3a/d

Table 14.--Continued.

57

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS as"
EVALUATED DATE 100 75 50
Diameter (cm)
First Flower 30 Jan 5.7a/d 5.8a/d 5.9a/d
20 Feb 6.3a/d 6.6a/d 5.8a/d
Second Flower 30 Jan 5.5a/d 5.8a/d 5.6a/d
20 Feb 5.9a/d 6.0a/d 5.8a/d
Third Flower 30 Jan 5.7a/d 5.6a/d 5.6a/d
20 Feb 6.2a/d 6.0a/d 5.6a/d
Number of Shoots Per Plant
Major Shoots 30 Jan 1.5a/d 1.3a/d 1.3a/d
20 Feb 1.8a/d 1.3a/d 1.4a/d
Minor Shoots 30 Jan 1.3a/d 0.5a/d 0.6a/d
20 Feb 0.5a/d 0.2a/d 0.4a/d
Total Shoots 30 Jan 2.8a/d 1.7a/d 1.9a/d
20 Feb 2.3a/d 1.5a/d 1.8a/d

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows
(each organ per date and parameter determined separately). Means
followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each
organ per treatment and parameter determined separately).

58

Table 15.-Effect of light intensity on the number of days to flower,
plant height, flower longevity, and diameter of the first
three flowers and number of shoots produced per plant of
'Park Princess'. Tuberous-roots were planted in 1975.

 

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS ex
EVALUATED DATE 100 75 50
Days to Flower
First Flower 30 Jan 69a/d 69a/d 77b/d
20 Feb 67a/d 74b/d 71ab/d
Second Flower 30 Jan 77a/d 75a/d 83a/d
20 Feb 75a/d 81a/d 80a/d
Third Flower 30 Jan 80a/d 79a/d 91b/d
20 Feb 78a/d 83a/d 86a/d
Plant Height (cm)
First Flower 30 Jan 30.3a/d 32.6a/d 40.9b/d
20 Feb 30.1a/d 31.5a/d 42.8b/d
Second Flower 30 Jan 32.3a/d 35.2a/d 46.7b/d
20 Feb 37.1a/d 36.4a/d 48.7b/d
Third Flower 30 Jan 36.5a/d 38.7a/d 52.1b/d
20 Feb 38.1a/d 37.8a/d 52.5b/d
Flower Longevity (Days)
First Flower 30 Jan 7.1a/d 7.7a/d 7.9a/d
20 Feb 7.7a/d 8.7a/d 6.9a/d
Second Flower 30 Jan 6.7a/d 7.2a/d 7.4a/d
20 Feb 7.7a/e 8.2a/e 7.9a/d
Third Flower 30 Jan 7.5a/d 6.1a/d 7.6a/d
20 Feb 8.3a/d 7.4a/d 7.7a/d

Table 15.--Continued.

59

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS %x
EVALUATED DATE 100 75 50
Diameter (cm)
First Flower 30 Jan 12.1a/d 11.8a/d 12.1a/d
20 Feb 12.4a/d 12.2a/d 12.2a/d
Second Flower 30 Jan 11.3a/d 11.1a/d 11.3a/d
20 Feb 11.6a/d 11.5a/d 11.7a/d
Third Flower 30 Jan 11.6a/d 11.6a/d 11.7a/d
20 Feb 11.4a/d 11.9a/d 11.6a/d
Number of Shoots Per Plant
Major Shoots 30 Jan 2.1a/d 1.7a/d 1.9a/d
20 Feb 1.5a/d 2.0ab/d 2.3b/d
Minor Shoots 30 Jan 1.3a/d 0.7a/d 1.1a/d
20 Feb 0.7a/d 1.2a/d 1.4a/d
Total Shoots 30 Jan 2.3a/d 1.5a/d 1.8a/d
20 Feb 2.2a/d 3.2ab/d 3.7b/d

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows
(each organ per date and parameter determined separately). Means
followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each
organ per treatment and parameter determined separately).

60

Table 16.--Effect of light intensity on the number of days to flower,
plant height, flower longevity, and diameter of the first
three flowers and number of shoots produced per plant of
'Kolchelsee'. Tuberous-roots were planted in 1976.

 

X

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS %
EVALUATED DATE 100 75 50
Days to Flower
First Flower 30 Jan 65a/d 66a/d 66a/d
20 Feb 66ab/d 64a/d 68b/d
Second Flower 30 Jan 70a/d 72a/d 73a/d
20 Feb 72a/d 70a/d 73a/d
Third Flower 30 Jan 74a/d 74a/d 80a/d
20 Feb 75a/d 72a/d 78a/d
Plant Height (cm)
First Flower 30 Jan 29.8a/d 34.5ab/d 40.4b/d
20 Feb 35.2a/d 35.7a/d 52.6b/e
Second Flower 30 Jan 34.9a/d 38.1a/d 47.2b/d
20 Feb 43.3a/e 40.3a/d 52.3b/d
Third Flower 30 Jan 38.1a/d 41.9ab/d 47.4b/d
20 Feb 46.6a/e 45.5a/d 62.8b/e
Flower Longevity (Days)
First Flower 30 Jan 6.6a/d 7.3a/d 6.6a/d
20 Feb 7.0a/d 6.8a/d 7.9a/e
Second Flower 30 Jan 6.0a/d 6.6a/d 6.3a/d
20 Feb 7.8a/e 8.0a/e 7.7a/e
Third Flower 30 Jan 6.1a/d 6.1a/d 6.6a/d
20 Feb 8.0a/e 8.1a/e 8.2a/e

Table 16.--Continued.

61

 

LIGHT INTENSITY TREATMENTS ex

 

 

 

 

 

PLANT ORGAN PLANTING
EVALUATED DATE 100 75 50
Diameter (cm)
First Flower 30 Jan 6.3a/d 6.3a/d 6.2a/d
20 Feb 6.1a/d 6.0a/d 5.9a/d
Second Flower 30 Jan 6.1a/d 5.7a/d 5.6a/d
20 Feb 5.8a/d 5.6a/d 5.9a/d
Third Flower 30 Jan 6.0a/d 5.9a/d 5.6a/d
20 Feb 5.8a/d 5.6a/d 5.8a/d
Number of Shoots Per Plant
Major Shoots 30 Jan 1.7a/d 1.4a/d 1.3a/d
20 Feb 1.3a/e 1.7a/d 1.5a/d
Minor Shoots 30 Jan 0.8a/d 0.9a/d 1.0a/d
20 Feb 0.4a/d 0.4a/d 0.2a/e
Total Shoots 30 Jan 2.6a/d 2.3a/d 2.4a/d
20 Feb 1.7a/d 2.0a/d 1.7a/d
Number of Flowers and Buds Per Plant
Total Flowers 30 Jan 7.5a/d 7.0a/d 8.0a/d
and Buds 20 Feb 9.0a/d 8.5a/d 6.9a/d

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows

(each organ per date and parameter determined separately).

Means

followed by the same letter following the slash (d,e) are not signigi-
cantly different by Tukey's test at .05 for pairs in columns (each

organ per treatment and parameter determined separately).

62

Table l7.--Effect of light intensity on the number of days to flower,
plant height, flower longevity, and diameter of the first
three flowers and number of shoots produced per plant of
'Park Princess'. Tuberous-roots were planted in 1976.

 

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS 1%"
EVALUATED DATE 100 75 50
Days to Flower
First Flower 30 Jan 70a/d 70a/d 75b/d
20 Feb 66a/e 66a/e 68a/e
Second Flower 30 Jan 74a/d 74a/d 79a/d
20 Feb 7la/d 73a/d 74a/d
Third Flower 30 Jan 76ab/d 75a/d 82b/d
20 Feb 73a/d 76a/d 78a/d
Plant Height (cm)
First Flower 30 Jan 41.4a/d 38.7a/d 56.5b/d
20 Feb 32.4a/e 38.4a/d 57.9b/d
Second Flower 30 Jan 44.8a/d 43.7a/d 58.8b/d
20 Feb 36.5a/e 42.8a/d 60.0b/d
Third Flower 30 Jan 47.9a/d 45.4a/d 62.4b/d
20 Feb 37.9a/e 44.3b/d 65.4c/d
Flower Loggevity (Days)
First Flower 30 Jan 6.9a/d 6.1a/d 8.2b/d
20 Feb 7.8a/d 8.9ab/e 9.3b/e
Second Flower 30 Jan 6.6a/d 6.5a/d 7.6a/d
20 Feb 7.7a/e 8.3ab/e 9.1b/e
Third Flower 30 Jan 6.9a/d 7.0a/d 7.7a/d
20 Feb 7.4a/d 8.4a/e 8.3a/e

Table l7.--Continued.

63

 

 

 

 

 

 

PLANT ORGAN PLANTING LIGHT INTENSITY TREATMENTS %x
EVALUATED DATE 100 75 50
Diameter (cm)
First Flower 30 Jan 12.3a/d 12.5a/d 12.3a/d
20 Feb 12.4a/d 12.7a/d 12.3a/d
Second Flower 30 Jan 11.8a/d 11.9a/d 11.8a/d
20 Feb 11.5a/d 11.7a/d 11.7a/d
Third Flower 30 Jan 11.0a/d 11.7a/d 11.5a/d
20 Feb 11.5a/d 11.4a/d 11.5a/d
Number of Shoots Per Plant
Major Shoots 30 Jan 1.9a/d 2.2a/d 1.9a/d
20 Feb 1.5a/d 1.3a/e 1.6a/d
Minor Shoots 30 Jan 0.5a/d 0.5a/d 0.6a/d
20 Feb 0.6a/d 0.4a/d 0.8a/d
Tetal Shoots 30 Jan 2.4a/d 2.7a/d 2.6a/d
20 Feb 2.0a/d 1.6a/e 2.4a/d
Number of Flowers and Buds Per Plant
TOtal Flowers 30 Jan 9.4a/d 10.1a/d 7.3b/d
and Buds 20 Feb 8.3a/d 5.7b/e 6.8ab/d

 

IMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows

(each organ per date and parameter determined separately).

Means

followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each

organ per treatment and parameter determined separately).

64

The increased heights of forced dahlias with lowered
light intensities confirms the findings of Biran and Halevy
(1973a) who reported increased internodal length of stock
plants of 'Orpheo' with 50 and 28% light levels. Similarly,
plant heights of both 'Ace' and 'Georgia' Easter lilies have
been increased with lowered light levels (Kohl and Nelson,
1963: Einert and Box, 1967). Heights of 'Ace' lilies had
been increased 14 cm by a 500 ft candle level while heights
of 'Georgia' lilies were increased 5.9 and 8.9 cm with 75
and 50% light levels.

The height increase of 'Kolchelsee' due to the
second planting date had also been noted by De Hertogh,
Blakely and Szlachetka, (1976) and may reflect the seasonal
increase in solar radiation and calories (Tables 3 and 4).
Thus, for a later planting date of 'Kolchelsee' the applica-
tion of ancymidol may be needed earlier to achieve proper
height control or the rate may have to be increased.

In other crops, the number of flowers per plant has
also been affected by lowered light levels. With a 50%
light level, the reduced number of flowers and buds as seen
in 'Park Princess' (Table 17) was similar to that reported
by Einert and Box (1967) with 'Georgia' lilies. In glad-
iglga 'Sans Souci' and 'Dr. Fleming' decreases in flowering
to 64 and 25% were reported with 25 and 20% light levels
(Shillo and Halevy, 1976a).

The delay in flowering at the 50% light level (Table

14, 15, and 17) probably reflects an overall reduction in

65

the photosynthetic rate of these plants. The promotion of
flowering in both cultivars during the 1976 forcing period
was an indicator of the yearly variation in light and
temperature conditions at the forcing location as well as
the year to year variation in plant material due to produc-
tion conditions. Obviously, these conditions will interact.

Increases in flower longevity of the second planting
date may reflect seasonal promotion of vigorous growth
(Tables 15, 16 and 17).

The increase in the number of shoots at the 50%
light level would have no commercial value since plant height

was unacceptable (Table 15).

Effects of Photoperiod

The greatest significant differences in all plant
parameters were obtained with the continuous treatments of
natural daylength, 4 hour night break, or 16 hour photo-
periods in both 1975 and 1976 (Tables 18, 19, 20 and 21) as
well as with the combination treatments in 1976 (Tables 20
and 21). In all these treatments, 100% of the plants
flowered.

With the 8 hour phot0period in 1975 (Table 18) 0 and
40% of 'Kolchelsee' flowered of the first and second plant-
ing dates respectively, while in the one planting date in
1976, 0% flowered (Table 20). Flowering of 'Park Prin-
cess' was affected to a lesser extent by the eight hour

treatment (Table 19) with 26 and 60% forming flowers Of the

66

Table 18.--Effect of photoperiod on the number of days to flower, plant
height, flower longevity, and diameter of the first three
flowers and number of shoots produced per plant Of
'Kolchelsee'. Tuberous-roots were planted in 1975.

 

PHOTOPERIOD TREATMENTSx

 

 

 

EVALUATSSAN DATE ING Natural 8 HourY 16 Hour 4 Hour
Day Night Break
Days to Flower

First Flower 30 Jan 68a/d - 72a/d 74a/d
20 Feb 64a/d 88.3b(40%) 67ac/d 73c/d

Second Flower 30 Jan 75a/d - 81ab/d 84b/d
20 Feb 69a/e - 72a/e 82b/d

Third Flower 30 Jan 79a/d - 86a/d 82a/d
20 Feb 72a/d - 78ab/d 85b/d

Plant Height (cm)

First Flower 30 Jan 25.8a/d - 26.2a/d 26.3a/d
20 Feb 32.6a/e 16.5b(40%) 31.4a/e 28.7a/d

Second Flower 30 Jan 29.5a/d - 31.9b/d 32.9b/d
20 Feb 35.7a/e - 33.0ab/d 30.9b/d

Third Flower 30 Jan 33.5a/d - 35.4a/d 34.8a/d
20 Feb 38.0a/e - 37.1a/d 33.2b/d

Flower Longevity (Days)

First Flower 30 Jan 6.9a/d - 7.7a/d 8.3a/d
20 Feb 6.3a/d 4.2b(40%) 6.3a/d 6.6a/e

Second Flower 30 Jan 6.9a/d - 7.6a/d 6.7a/d
20 Feb 6.0a/d - 7.5a/d 7.1a/d

Third Flower 30 Jan 6.9a/d - 7.2a/d 7.4a/d

 

 

67

Table 18.--Continued.

 

PHOTOPERIOD TREATMENTS"

 

 

 

PLANT ORGAN PLANTING
Natural 8 HourY 16 Hour 4 Hour
EVALUATED DATE Day Night Break
Diameter (cm)

First Flower 30 Jan 5.9a/d - 5.8a/d 5.9a/d
20 Feb 6.3a/d 5.2b(40%) 6.2a/d 6.2a/d

Second Flower 30 Jan 5.6a/d - 5.7a/d 5.9a/d
20 Feb 5.9a/d - 5.9a/d 5.9a/d

Third Flower 30 Jan 5.6a/d - 5.9a/d 5.8a/d
20 Feb 5.6a/d - 5.9a/d 5.8a/d

Number of Shoots Per Plant

Major Shoots 30 Jan 1.6a/d 1.2a/d 1.7a/d 1.6a/d
20 Feb 1.5a/d 1.8a/d 1.6a/d 1.7a/d

Minor Shoots 30 Jan 1.1a/d 0.8a/d 1.1a/d 0.9a/d
20 Feb 0.5a/d 0.5a/d 0.3a/d 0.3a/d

Total Shoots 30 Jan 2.7a/d 1.8a/d 2.8a/d 2.5a/d
20 Feb 2.0a/d 2.3a/d 1.9a/d 2.0a/d

 

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows
(each organ per date and parameter determined separately). Means
followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each
organ per treatment and parameter determined separately).

YMaximum percent of the plants flowering is given.

68

Table 19.-Effect of phOtOperiod on the number of days to flower, plant
height, flower longevity, and diameter of the first three
flowers and number of shoots produced per plant of 'Park
Princess'. Tuberous-roots were planted in 1975.

 

PHOTOPERIOD TREATMENTSx

 

 

 

PLANT ORGAN PLANTING
Natural 8 HourY 16 Hour 4 Hour
EVALUATED DATE Day Night Break
Days to Flower
First Flower 30 Jan 71a/d 54b/d(26%) 82c/d 82c/d
20 Feb 68a/d 51b/d(60%) 75c/d 74c/d
Second Flower 30 Jan 78a/d - 89b/d 88b/d
20 Feb 75a/d 63b(60%) 83c/e 83c/e
Third Flower 30 Jan 82a/d - 90ab/d 99b/d
20 Feb‘ 78a/d - 90a/d 89a/d
Plant Height (cm)
First Flower 30 Jan 31.2a/d 24.3b/d(26%) 27.0ab/d 27.2ab/d
20 Feb 30.1ab/d 29.0ab/e(60%) 31.9a/e 25.7b/d
Second Flower 30 Jan 34.1a/d - 32.9a/d 32.6a/d
20 Feb 37.1a/d 34.0a/b(60%) 35.7a/d 29.6b/d
Third Flower 30 Jan 36.3a/d - 34.3a/d 35.0a/d
20 Feb 38.1a/d - 40.7a/e 33.7b/d
Flower Longevity (Days)
First Flower 30 Jan 9.4a/d 6.2b/d(26%) 7.9ac/d 7.3a/d
20 Feb 7.7ab/e 6.6a/d(60%) 8.3ab/d 8.7b/d
Second Flower 30 Jan 7.9a/d - 7.7a/d 8.2a/d
20 Feb 7.7a/d 7.0a(60%) 8.2a/d 8.9a/d
Third Flower 30 Jan 7.0a/d - 8.3a/d 8.3a/d
20 Feb 8.3a/d - 6.5a/e 6.4a/e

 

 

69

Table 19.--Continued.

 

PHOTOPERIOD TREATMENTSx

 

 

 

 

PLANT ORGAN PLANTING
Natural 8 HourY 16 Hour 4 Hour
EVALUATED DATE Day Night Break
Diameter (cm)

First Flower 30 Jan 11.7a/d 10.1b/d(26%) 13.4c/d 14.3c/d
20 Feb 12.4a/e 11.1b/e(60%) 13.6c/d 13.0ac/d

Second Flower 30 Jan 11.4a/d - 13.3b/d 13.4b/d
20 Feb 11.6a/d 10.3b(60%) 12.5ac/d 13.2c/d

Third Flower 30 Jan 11.3a/d - 12.7b/d 13.0b/d
20 Feb 11.4a/d - 12.4b/d 12.1ab/e

Number of Shoots Per Plant

Major Shoots 30 Jan 1.9a/d 1.5a/d 2.0a/d 1.9a/d
20 Feb 1.5ab/d 1.0b/d 1.9a/d 1.9a/d

Minor Shoots 30 Jan 1.0a/d 0.5a/d 0.8a/d 1.0a/d
20 Feb 0.7a/d 0.6a/d 2.3b/e 0.8a/d

Total Shoots 30 Jan 2.9a/d 2.0a/d 2.8a/d 2.9a/d
20 Feb 2.2ab/d 1.6b/d 3.2a/d 2.7a/d

 

xMeans followed by the same letter preceding the slash (a,b,c)
are not significantly different by Tukey's test at .05 for single rows

(each organ per date and parameter determined separately).

Means

followed by the same letter following the slash (d,e) are not signifi-
cantly different by Tukey's test at .05 for pairs in columns (each
organ per treatment and parameter determined separately).

yMaximum percent of the plants flowering is given.

70

 

 

 

 

 

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73

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74

respective planting dates in 1975. In 1976 (Table 21) 78,
57, and 7% of the plants formed first, second, and third
flowers respectively. The increases in percent flowering
from the first to second planting date and from 1975 to
1976 reflect variation in forcing conditions and/or plant
material.

Under the 8 hour photOperiod, flowers Opened 17 days
earlier than under natural daylength conditions but were
abnormal, having a single row of ray florets with 'open-eye'
centers. Plant height, flower longevity, flower diameter,
and the number of flowers and buds per plant were signifi-
cantly decreased by this treatment and vegetative growth
was severely retarded.

Plants of 'Kolchelsee' and 'Park Princess' under the
natural daylength treatment flowered in 68 and 71 days in
1975 (Tables 18 and 19) and in 1976 (Tables 20 and 21) in
65 and 68 days for the respective cultivars.

Flowering was delayed in plants grown under the 16
hour photoperiod, 4 hour night break, and some of the treat-
ments which combined these regimes with the natural day-
length photoperiod. The mean delay in flowering was six
days for 'Kolchelsee' and seven days for 'Park Princess'.
Flower longevity was also increased in both cultivars but
flower diameters of only 'Park Princess‘ were increased.
Means for plant height, the number of shoots, and the number

of flowers and buds per plant were not different.

75

Previous investigators had reported that photoperiods
of natural daylength, short days, and long days affected the
flowering stage of dahlias (Zimmerman and Hitchcock, 1929,
Maatsch and Rfinger, 1954, Yasuda and Yokoyama, 1959). How-
ever, since the locations of the experiments and the parti-
cular seasonal conditions prevailing had altered the natural
daylength in each experiment, it is difficult to make direct
comparisons of the results. Their experiments showed
however, that there were great cultivar differences in
responses to the various photOperiods. Also, since their
plants had originated from seeds, cuttings, or tuberous-
roots, this factor affected the responses.

Since flower initiation is completed within three
weeks after the planting of the tuberous-roots (Krijthe,
1938), effects of photoperiod on bud initiation and develOp-
ment were determined using continuous treatments from the
time of planting. Photoperiod conditions applied after the
first three weeks of growth and continued until flowering
would primarily affect floral development. Since 'Kolchel-
see' and 'Park Princess' formed floral buds under all the
photoperiod treatments, it was apparent that the critical
daylength for bud initiation in these cultivars must be less
than eight hours. Floral develOpment, however, was primarily
affected by the photoperiod treatments.

The adverse effects of the eight hour photoperiod on
the flowering stage of 'Kolchelsee' and 'Park Princess' with

reduced flowering, abnormal floral development, and retarded

76

vegetative growth has been similarly reported with tuberous-
rooted dahlias of 'Broeder Justinus' and 'Finesse Anversoise'
with 8-11 hour photoperiods (Maatsch and Rfinger, 1954).

The increased percent of flowering of the second
planting date during the 8 hour photoperiod reflected the
seasonal increase in light and energy levels during the
restricted hours (Tables 3 and 4). Konishi and Inaba (1966)
reported a similar increase from 35% flowering in 'Akane'
with a 12 hour photOperiod in the autumn compared to 70%
flowering in the spring with the same photoperiod. The role
of short day conditions in promoting tuberization of many
dahlia cultivars has been well established (Zimmerman and
Hitchcock, 1929, Moser and Hess, 1968), and it is directly
antagonistic to the vegetative growth stage (Moser and Hess,
1968). Similarly the flowering stage is greatly affected.

Abnormal flower development in 'Park Princess' seen
with the 8 hour photoperiod was similarly reported in 'Newby'
and 'Chorus Girl' with short day conditions in January and
February (Canham, 1969) and in 'Finesse Anversoise' receiv-
ing photoperiods of 11 hours or shorter (Maatsch and Rfinger,
1954). For 'Park Princess' the critical daylength for
normal flower development must exceed 8 hours.

The delayed flowering of 'Kolchelsee' and 'Park
Princess' under long day type treatments has been reported
for 'John Erlich' grown under a 16 hour photoperiod (Zimmer-

man and Hitchcock, 1929). Flowering of seedlings of 'Unwin'

77

and 'Coltness' were similarly delayed by daylengths exceed-
ing 14 1/2 hours (Botacchi, 1958), while 'Broeder Justinus'
and 'Finesse Anversoise' were delayed an average of 20 days
with a 14 hour photoperiod (Maatsch and Rfinger, 1954).
Although cultivar response varied, treatments of
natural daylength exceeding at least 10 hours at planting
appear adequate for forcing. Adequate vegetative growth

and rapid flowering can be obtained.

Effects of Hydrogel

 

For both cultivars, forcing parameters were not
greatly affected by the hydrogel treatments (Tables 22 and
23) and there were no adverse effects. At maturity, the
plants required increased amounts of water and both rates
of hydrogel were adequate to prevent the afternoon wilting
that was normally observed.

Perhaps, hydrogel could be effective in increasing
the shelf life of plants during shipping and marketing.
Treatments could increase the amount of time between appli-
lcations of water by consumers, but these effects were not

determined.

78

Table 22.--Effect of hydrogel on the number of days to
flower, plant height, flower longevity, and
diameter of the first three flowers and number
of shoots produced per plant of 'Kolchelsee'.
Tuberous-roots were planted on 4 February, 1975.

 

 

 

 

 

 

 

 

PLANT ORGAN HYDROGEL TREATMENTS (GRAMS PER, CUBIC FT.)x
EVALUATED 0 339.6 226.4
Days to Flower
First Flower 65a 68a 66a
Second Flower 72a 79b 73ab
Third Flower 80a 86b 81ab
Plant Height (cm)
First Flower 26.2a 25.2a 27.3a
Second Flower 29.8a 29.5a 31.2a
Third Flower 33.8a 32.7a 34.1a
Flower Longevity (Days)
First Flower 7.0a 7.1ab 7.6b
Second Flower 6.9a 7.7b 7.3ab
Third Flower 6.3a 7.2a 6.9a
Diameter (cm)
First Flower 6.0a 5.9a 6.1a
Second Flower 5.7a 5.7a 6.0a
Third Flower 5.9a 5.8a 6.0a
Number of Shoots Per Plant
Major Shoots 1.5a 1.7a 1.5a
Minor Shoots 0.7a 1.1a 0.7a
Total Shoots 2.1a 2.7a 2.2a

 

xMeans followed by the same letter (a,b,c) are not
significantly different by Tukey's test at .05 for single
rows (each organ per parameter determined separately).

79

Table 23.--Effect of hydrogel on the number of days to
flower, plant height, flower longevity, and
diameter of the first three flowers and number
of shoots produced per plant of 'Park Princess'.
Tuberous-roots were planted on 4 February, 1975.

 

 

 

 

 

 

PLANT ORGAN HYDROGEL TREATMENTS (GRAMS PER CUBIC FT.)x
EVALUATED 0 339.6 226.4
Days to Flower
First Flower 76a 72a 74a
Second Flower 80ab 76a 83b
Third Flower 85ab 82a 88b
Plant Height (cm)
First Flower 31.4a 32.0a 31.1a
Second Flower 32.8a 34.6a 36.2a
Third Flower 34.1a 37.3b 37.6b
Flower Longevity_(Days)
First Flower 7.9a 7.9a 7.7a
Second Flower 6.2a 7.8b 7.3b
Third Flower 6.8a 6.6a 6.5a

Diameter (cm)

First Flower 12.5a .12.4a 12.1a
Second Flower 12.3a 12.1ab 11.9b
Third Flower 11.5a 12.6b 11.8a

Number of Shoots Per Plant

Major Shoots 2.5a 2.2a 2.3a
Minor Shoots 1.8a 1.7a 2.5a
Total Shoots 4.4a 3.9a 4.8a

 

‘xMeans followed by the same letter (a,b,c) are not
significantly different by Tukey's test at .05 for single
rows (each organ per parameter determined separately.

CONCLUSIONS

Cultivars differed in their response to the various
environmental factors tested.

The parameters: shoot number, flower diameter, and
flower longevity were minimally affected by the
treatments and were mainly a cultivar characteristic.
Year to year variation due to variation in produc-
tion and forcing conditions was reflected in data
for 1975 and 1976 for comparable treatments and
cultivars.

Fertilization of tuberous-roots during forcing pro-
moted earlier flowering and plant development.
Precise levels for fertilization were not determined
but an application of Osmocote (14-14-14), (18-6-
12), and (18-9-12) or (20-20-20) as a soluble ferti-
lizer were satisfactory.

Light intensity levels of 100 or 75% gave good height
control and promoted rapid flowering with no other
adverse effects. At 50% light levels, plant heights

exceeded acceptable ranges and flowering was delayed.

80

81

The 8 hour photoperiod severely retarded vegetative
growth, reduced the percent of plants flowering,
and caused abnormal flowering. Natural daylengths
of at least 10 hours at planting and increasing to
14 hours produced good quality plants. Long day
treatments of either 16 hours or a 4 hour night
break delayed flowering.

Responses to both day and night temperatures were
demonstrated. The 27/16°C treatment promoted rapid
flowering with satisfactory height control. Higher
temperatures accelerated flowering but were delete-
rious for satisfactory growth and development.
Lower temperatures delayed flowering and increased
plant height.

By controlling the interaction of these greenhouse
factors, the production of high quality pot plants
from tuberous-rooted cultivars for spring markets

is feasible.

LITERATURE CITED

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