Arboriculture & Urban Forestry 42(3): May 2016 costs of varying container sizes have yet to be fully evaluated to determine which container size affords the most advantageous opportunity to consumers. Although container size establishment has been considered by several researchers (Gilman et al. 1998; Struve 2009; Gilman and Masters 2010; Gil- man et al. 2010; Lambert et al. 2010; Gilman et al. 2013), extensive research has yet to be conducted, especially in regards to differences across environ- ments. With trees being offered to the public in an ever-increasing array of sizes, it is important to determine the initial growth responses of various container-grown trees for different landscape envi- ronments. Geography influences trees’ responses to varying light levels, photoperiods, and precipitation (Teskey and Hinckley 1986; Chapin et al. 1987), thus impacting the type of trees that can be grown (Abrams and Kubiske 1990). It is oſten generally accepted that smaller-sized planting stock estab- lishes more quickly aſter transplanting than larger stock (Struve 2009; Gilman et al. 2010; Gilman et al. 2013). Lambert et al. (2010) investigated three sizes of containers for three species in forestry conditions, but only smaller sizes were tested [i.e., 3.5 L (#1), 11.7 L (#3), and 23.3 L (#7)], and no information was provided relative to the genotypic background of the plants—and so size may have been confounded with genotypes or nursery production conditions. The purpose of this study was to determine if differential growth rates existed during the first year of establishment in the landscape with trees representing various ornamental landscape species grown in a wide range of container sizes, and if those initial post-transplant growth responses varied between two contrasting locations. MATERIALS AND METHODS Clonal selections of Vitex agnus-castus L. (spreading multi-stemmed small tree), Acer rubrum L. var. drummondii (Hook. & Arn. ex Nutt.) Sarg. (single- stemmed deciduous broadleaved shade tree), and Taxodium distichum (L.) Rich. (single-stemmed de- ciduous conifer) were chosen due to their wide-spread use in the regional nursery trade and their represen- tation of a variety of classes of landscape trees. In or- der to best represent contrasting environments that utilize all three species regularly in the landscape, two U.S. locations were selected; College Station, Texas (seasonally xeric) and Starkville, Mississippi (mesic). 171 Beginning spring 2011, tip cuttings (8–10 cm long) of Acer rubrum var. drummondii ‘Maroon’, Vitex agnus-castus (unnamed white flowering clone), and Taxodium distichum (Test Clone TX8DD38) were taken from containerized clonal sources maintained in College Station, Texas, U.S. The basal end of these cuttings was then dipped in a liquid rooting hormone containing indolebutyric acid (IBA): naphthalene acetic acid (NAA) at a 3:1 concentrate (2,500 mg•L-1 IBA/ 1,250 mg•L-1 NAA) to water ratio for five seconds (Dip ’n Grow® Inc., Clackamas, Oregon, U.S.). Cuttings were placed in 36 cm × 51 cm × 10 cm deep flats (Kadon Corp., Dayton, Ohio, U.S.) filled with coarse perlite (Sun- shine Perlite #3 4cf SUGRPLITE Sun Gro Horticul- ture Canada LTD, Seba Beach, Alberta, Canada) on an intermittent mist bench in a poly-covered green- house. Intermittent mist was applied at 16 minute intervals for 20-second durations using reverse osmosis water from one hour before sunrise to one hour aſter sunset. Rooted cuttings were then potted in 3.5 L (#1) black plastic pots (Nursery Supplies, Inc., Kissimmee, Florida, U.S.) contain- ing Metro-Mix 700 media (Sun Gro Horticulture Canada Ltd, Vancouver, British Columbia, Canada). Nurserymen used ANSI Z60.1 container class standards (American Association of Nurseryman 2004) caliper and height to determine the appro- priate container size for individual trees (Table 1). Therefore, as the cuttings grew, trees were trans- planted to successively larger container sizes, 11.7 L (#3), 23.3 L (#7), 97.8 L (#25), and 175.0 L (#45) when trees reached appropriate size for the current container (Figure 1). This process was repeated throughout a two-year period until 18 trees of each container size for each species were produced, with initial trees being transplanted to #45 at nearly the same time propagation of cuttings for the #1 con- tainers began. During the repotting process, trees were removed from their initial container, roots were broken up by hand to disrupt circling roots, and trees were repotted in appropriate sized black plastic pots (Nursery Supplies, Inc., Kissimmee, Florida, U.S.) containing Metro-Mix 700 media (Sun Gro Horticulture Canada Ltd, Vancouver, British Columbia, Canada). As trees were pro- duced, they were amended with 15N-3.9P-9.9K controlled release fertilizer (Osmocote® Plus, Scotts Co., Marysville, Ohio, U.S.) every spring ©2016 International Society of Arboriculture
May 2016
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