74 Gilman et al.: Effect of Container Type and Root Pruning on Growth and Anchorage Aſter Planting ment following planting in slightly larger contain- ers. It is not clear if root deflection in much larger containers typical of the landscape nursery indus- try would also result in compromised anchorage. Distributing root tips in the lateral (horizon- tal) position throughout the root ball instead of vertically—causing a collection of circling roots at the container bottom—on young mahogany (Gilman and Paz 2013) in #3 containers allowed many lateral roots to grow into landscape soil in a more natural position parallel to the soil sur- face. Young trees with an abundance of straight roots inside the root ball at planting appear bet- ter secured to soil aſter planting than those with bent roots (Gilman and Harchick 2013). Despite differences in root architecture at, and aſter plant- ing, there may be little impact on shoot and trunk growth (Ruter 1993; Marshall and Gilman 1998). One method of managing root architecture is manual root pruning. Early work showed that man- ual root pruning of tree seedlings raised in contain- ers reduced root defects (Harris et al. 1971a; Harris et al. 1971b) and produced more symmetrically distributed lateral roots aſter planting (Krasowski 2003). One recent study showed that light cutting of circling roots on shrubs enhanced the amount of roots growing into substrate of the slightly larger container (Blanusa et al. 2007). Slicing (Quercus virginiana Mill., Gilman et al. 2009) or shaving (Acer rubrum, Gilman et al. 2010b) the #3 con- tainer periphery when shiſting into a #15 container improved root system quality by removing roots that grew down, around, and up the container wall. There is more experience studying the impact of root pruning during the process of planting into field soil than when shiſting to larger nurs- ery containers. Gilman et al. (1996) showed that cutting Burford holly (Ilex cornuta ‘Burfordii’) #3 root balls from top to bottom (slicing or scoring) at planting resulted in a redistribution of roots, not an increase in roots, compared with non-pruned controls. Harris et al. (2001) reported root-pruning treatments (5, 10, or 15 cm below soil) on pin oak (Quercus palustris Münchh.) liners in containers did not affect root length following planting, but root pruned trees had more main lateral roots (>2 mm diameter) originating from the primary seed- ling radicle when compared to control. Krasowski and Owens (2000) found that, despite a smaller ©2016 International Society of Arboriculture root ball at planting, root systems of mechanically pruned Picea glauca (Moench) Voss seedlings pro- duced greater root growth in field soil than control or chemically root pruned treatments. Removing all roots by shaving the periphery of several tree taxa has shown to be very effective at almost eliminating deflected roots within the root ball (Gilman et al. 2010b; Gilman et al. 2015), but its impact on roots and growth aſter planting into soil remains untested. The goal of this project was to determine if nurs- ery container type, root pruning in the nursery, and tree orientation during production influence growth and anchorage aſter planting trees into land- scape field soil. Specific objectives were to relate root architecture within the planted root ball—described in the companion study (Gilman et al. 2015)—with anchorage 26 months aſter planting from four con- tainer sizes, and with growth and root architecture measured when trees were five-years-old. Differ- ent root morphologies were induced by growing trees in eight different types of containers and by root pruning while shiſting to larger containers. MATERIALS AND METHODS A cultivar of Acer rubrum (‘Florida Flame’) was cho- sen for this study because red maple and hybrids are common shade trees grown throughout much of the United States. ‘Florida Flame’ red maple is propa- gated by rooting current year’s shoots removed from parent trees; use of clonal trees should reduce root system variability among replicate trees com- pared to a cultivar graſted onto seedling root stock. Planting into Containers and Land- scape Soil In April 2008, 384 uniform rooted cutting liners (13 cm tall) in circular (5.1 cm top diameter, 13 cm tall ribbed containers, 38 Groovetube, Grow- ing Systems, Inc., Milwaukee, Wisconsin, U.S.) were shiſted (planted) into eight different #3 (ap- proximately 11 L) container types described fully in Gilman et al. (2010a). The container types were smooth sided (SS, Nursery Supplies, Inc., Cham- bersburg, Pennsylvania, U.S.); SmartPot® (SP, Root Control, Inc., Oklahoma City, Oklahoma, U.S.); RootBuilder® (RB) and RootMaker® (RM, Root- Maker® Products Company, LLC, Huntsville, Alabama, U.S.); Fanntum™ (FN, Fanntum Products, Inc., Statesville, North Carolina, U.S.); Florida Cool
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