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J. Roger Harris

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Lisa E. Richardson-Calfee and J. Roger Harris

Prudent landscape professionals can enhance chances for successful establishment by timing tree transplant operations to coincide with ideal seasonal conditions. However, transplant timing is usually determined by economic factors, resulting in trees being transplanted at times that are unfavorable for their survival and growth. Knowledge of the effects of season of transplanting on the establishment of landscape trees can help assure the highest probability of success, especially since special post-transplant management may be required if trees are transplanted at unfavorable times. This manuscript reviews past and current research on the effects of transplant timing on landscape establishment of deciduous shade trees. Specific results are summarized from several key studies.

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J. Roger Harris and Susan D. Day

Root flares of landscape trees are increasingly found to be much deeper than their forest counterparts, indicating that their root systems have been situated deeper in the soil. Planting deeply in production containers contributes to this phenomenon, yet the consequences of deep planting in production containers or the consequences of any adjustments made to planting depth at the time of transplant on growth in the landscape have not been reported for many species. Container-grown (11.4 L) liners of Tilia cordata Mill. (littleleaf linden) and Quercus palustris Münchh. (pin oak) were planted in 50-L containers with the first main lateral roots (structural roots) at substrate-surface grade or 10 cm or 20 cm below grade (deep planting). Trees were grown in the 50-L containers for two growing seasons and in a simulated landscape for three additional seasons after transplanting with the top of the container substrate at soil level or with some roots and substrate removed such that the original structural roots were just below the soil surface (remediated). Deep planting pin oak, but not littleleaf linden, slowed growth during container production; however, the effect did not persist after transplanting. Remediation of the 20-cm-deep pin oaks slowed growth during all three post-transplant years. Littleleaf linden remediation slowed growth for the first season after transplanting to a simulated landscape for 10-cm-deep trees and for the first two seasons for 20-cm-deep trees. Evaluation of pin oak root systems 3 years after transplanting revealed vigorous growth of non-deflected adventitious roots that had formed on the trunks of deep trees, and these roots appeared to be developing into main structural roots. No adventitious roots were present on littleleaf linden; instead, deflected roots grew and produced deformed root systems. Deep planting of linden reduced suckering; however, we conclude that remediation of deep-planted littleleaf linden is warranted as a result of potential hazards from trunk-girdling roots. In some species such as pin oak, non-deflected, strong adventitious root systems may assume the role of structural roots and diminish the effect of deflected and circling roots systems formed during container production. Remediation of these trees is likely not as critical as for species without abundant adventitious roots.

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J. Roger Harris, Patricia Knight and Jody Fanelli

Two rootball sizes as well as a nontransplanted control were randomly assigned to Acer saccharum Marsh. (sugar maple) trees in four adjacent nursery rows at Waynesboro Nurseries in Waynesboro, Va. One size (75 cm in diameter) corresponded to the American Association of Nurserymen standards. The other rootball size was 90 cm in diameter. Trees were transplanted just before bud swell or during shoot elongation. Rootball size had no effect on height, stem diameter, or twig growth, total nonstructual leaf nitrogen content (LNC), or total stem nonstructual carbohydrate (TNC). Height growth was reduced by 81%, stem diameter growth by 71%, and twig growth by 82% for trees transplanted before bud swell compared to nontransplanted trees. LNC was 25% more on transplanted trees than on nontransplanted trees, presumably due to a dilution effect. TNC was 20% higher on transplanted compared to nontransplanted trees. Growth was severely curtailed on late-transplanted trees for all characteristics measured compared to all other treatments.

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J. Roger Harris, Patricia Knight and Jody Fanelli

The effect of fall vs. spring transplanting was tested on landscape-sized Chionanthus virginicus L. at a research farm in Blacksburg, Va. Two fall transplanting dates (11 Nov. and 1 Dec. 1994) were selected so that soil temperatures were decreasing and near 10 °C for the earlier fall date (11 Nov.) and decreasing and near 5 °C for the later fall transplanting date (1 Dec.). The spring date (14 Mar. 1995) was selected so that soil temperatures were increasing and near 5 °C. All trees were transplanted with rootballs of native soil wrapped in burlap (B&B). Fringe tree was clearly tolerant of fall transplanting. Trees transplanted on 11 Nov. had a larger leaf area 1 month after bud set the next summer and had wider canopies and more dry mass of new roots at leaf drop than trees transplanted on the other dates. Trees transplanted on 14 Mar. had less total leaf area, leaf dry mass, and lower maximum root extension into the backfill soil than trees transplanted on 11 Nov. or 1 Dec. No root growth occurred beyond the original rootball until about early July (1 month after bud set) in any treatment, suggesting that first season posttransplant irrigation regimes need to focus on rootballs, not surrounding soil areas.

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J. Roger Harris, Richard Smith and Jody Fanelli

Rapid posttransplant root growth is often a determining component of successful establishment. This study tested the effect of transplant timing on first-season root growth dynamics of bare-root Turkish hazelnut trees. Trees were either harvested and planted in the fall (F-F), harvested in the fall and planted in the spring after holding in refrigerated storage (F-S), or harvested and planted in the spring (S-S). All trees were transplanted into 51-L containers, adapted with root observation windows. Root growth began in F-F and F-S trees 1-2 weeks before spring budbreak, but was delayed in S-S trees until ≈3 weeks after budbreak. Budbreak was 6 days earlier for fall-harvested than for spring-harvested trees. No new roots were observed before spring. Root length accumulation against observation windows (RL) was delayed for S-S trees, but rate of increase was similar to F-F and F-S trees soon after growth began. Seasonal height, trunk diameter growth, and RL were similar among treatments. Surface area of two-dimensional pictures of entire rootballs was not correlated with seasonal RL.

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J. Roger Harris, Jody Fanelli and Paul Thrift

Description of early post-transplant root growth will help formulate best transplanting strategies for landscape trees. In this experiment, the dynamics of early root system regeneration of sugar maple (Acer saccharum Marsh. `Green Mountain') and northern red oak (Quercus rubra L.) were determined. Field-grown 4-year-old trees were transplanted bare-root into outdoor root observation containers (rhizotrons) in Oct. 1997, Nov. 1997, or Mar. 1998. All trees were grown in the rhizotrons until Oct. 1998 and then transplanted, with minimally disturbed rootballs, to field soil and grown for an additional two years. October-transplanted trees of both species began root regeneration earlier and regenerated more roots, as judged by accumulated root length on rhizotron windows, than Nov.- or March-transplanted trees. Median date for beginning root extension for sugar maples was 48, 22, and 0 days before budbreak for October-, November-, and Marchtransplanted trees, respectively. Median date for beginning root extension for northern red oak was 4, 21, and 14 days after budbreak for October-, November-, and Marchtransplanted trees, respectively. Height and trunk diameter growth were similar for all treatments within each species for 3 years after application of treatments. Early fall transplanting will result in earlier first season post-transplant root growth for sugar maple and northern red oak. Earlier post-transplant root growth will likely increase resistance to stress imposed by harsh landscape environments.

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J. Roger Harris and Edward F. Gilman

Growth and physiological responses before and after transplanting to a simulated landscape were studied for `East Palatka' holly (Ilex ×attenuata Ashe `East Palatka') grown in plastic containers (PC), in the ground in fabric containers (FC), or in the ground conventionally. At the end of a 15-month production period, trees grown in PC had more shoot dry weight and leaf area than trees grown in FC, and they had thinner trunks than field-grown trees. Root balls on harvested field-grown trees contained 55% and those grown in FC 65% of total-tree root surface area. Trees transplanted from FC had the lowest predawn leaf xylem potential and required more frequent post-transplant irrigation than trees grown in PC or in the ground. Carbon assimilation rate and stomata1 conductance in the first week after transplanting were highest for trees planted from PC. Dry weight of regenerated roots was similar for all production methods 4 months after transplanting from the nursery, but trees grown in PC had SO% more regenerated root length, and the roots extended further into the back-fill soil.

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Matt Kelting, J. Roger Harris, Jody Fanelli and Bonnie Appleton

Application of biostimulants, humate-based products marketed as aids to plant establishment, may increase early post-transplant root growth and water uptake of landscape trees. We tested three distinct types of biostimulants on root growth and sapflow of balled and burlapped red maple (Acer rubrum L. `Franksred') trees. Treatments included: humate, 1) as a wettable powder formulation, applied as a soil drench; 2) as a liquid formulation to which various purported root growth—promoting additives had been added, also applied as a soil drench; 3) as a dry granular formulation, applied as a topdress; and 4) a nontreated control. Root growth was monitored through single-tree rhizotrons, and sap flow was measured with a heat balance sapflow system. Roots were first observed in the rhizotron windows 38 days after planting. No biostimulant-treated trees had more root length than nontreated controls, and the two soil drench treatments had the lowest root length throughout the 20 weeks of post-transplant observation. All biostimulants increased sapflow.

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J. Roger Harris, Alex Niemiera, Jody Fanelli and Robert Wright

Two experiments tested the effects of root pruning on growth during first-season production of pin oak (Quercus palustris Muenchh.). Experiment one tested the effect of root pruning developing radicles at 5, 10, or 15 cm (2, 4, or 6 inches) below the substrate surface. After 11 weeks, total root length was not affected by root pruning, but root-pruned seedlings had more main lateral [>2-mm (0.08-inch) diameter] roots than those that were not root pruned. Shallow pruning increased the number of main lateral roots. Experiment two tested the effect of initially producing plants in different-depth bottomless containers [5, 10, 15, or 20-cm (2, 4, 6, or 8-inch) depth] on growth after transplanting to #2 [6 L (1.6 gal)] containers. Shoot and root growth in #2 containers were lowest when plants were originally produced in 5-cm-deep containers. Plants with the greatest height and highest root:shoot ratios were obtained when plants were grown initially in 10-cm-deep containers. Predicted optimum depth of bottomless containers from regression equations ranged from 11.3 cm (4.5 inches) to 14.2 cm (5.5 inches) for the different growth parameters measured. The importance of these findings are: Pruning developing radicles of pin oak seedlings increases the number of main lateral roots but not overall root length. Growers can maximize growth in #2 containers by initially growing in 10-cm-deep bottomless containers before transplanting to #2 containers.