Container-grown shade trees make up an increasing proportion of nursery stock, yet arborists report concerns about root defects associated with trees grown in smooth-sided containers, such as circling roots, persisting in the landscape post-transplant. The objective of this study was to determine the effect of root modifications at planting on establishment, survival, and growth of container-grown October Glory® red maple, columnar tulip poplar, and 'Bloodgood' London planetrees. Modifying roots before planting increased leaf scorch for tulip poplar and red maple trees. Nearly all trees bare-rooted before planting in July had severe die-back. Survival was excellent for all red maples and planetrees planted in May regardless of treatment. Survival for tulip poplar trees that were bare-rooted in May was 50%; all tulip poplars that were bare-rooted in July died. Bare-rooting increased tree stress immediately after planting, however, leaf water potential values for the rest of 2018 and throughout 2019 suggest that water status of trees with modified root systems achieved an equilibrium by reducing whole-tree water loss as functional leaf area was reduced. Root biomass outside the original root-ball did not differ among root modification treatments two years post-transplant. However, bare-rooting reduced the proportion of circling roots compared to control trees for all species. Shaving reduced circling roots compared to control trees for tulip poplar and planetrees. For practitioners interested in trialing these techniques, we advise performing root modifications in the dormant season and avoiding species known to be difficult to transplant bareroot (e.g., oaks, hackberry, tulip poplar).
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