Arboriculture & Urban Forestry 36(3): May 2010 mm) magnolias (Table 3). This was not surprising because mag- nolia generates roots primarily from the end of the stem when rooting cuttings, not along the stem according to many propa- gators (e.g., Todd Gentry, Total Quality Liners, Inc., Groveland FL). Cathedral Oak (Gilman et al. 2006), and probably other trees lose their capacity to generate roots along the buried stem as they grow older. Shallower planted trees into #3 had fewer roots over the flare because it was higher in the substrate pro- file and some deflected roots grew under main flare roots. As shown for Cathedral Oak (Gilman et al. 2006), planting deeply (64 mm) into #15 for elm and maple resulted in more serious defects than planting deeply (64 mm) into #3 containers (Table 2). The older trees apparently had lost capacity to gener- ate new adventitious roots from the buried portion of the stem. As a result, elm and maple planted deeply into #15 containers had more roots growing around the trunk, deeper root flare, and more root length over the flare compared to shallow planting. In contrast, magnolia planting depth into #15 containers had no impact on defects. Magnolia roots were less likely to grow up into substrate placed over the flare as compared to elm and maple when shifted into a #15. The reason for this is not clear. Stem Girdling Roots Planting deeply into containers may be more problematic than planting deeply into a field nursery because roots in containers are deflected around, up, and back toward the trunk (Gilman et al. 2010a). The result is a container root ball with more root density than a root ball dug from field soil (Harris and Gilman 1993; Gilman and Beeson 1996; Marshall and Gilman 1997). Roots of nursery-sized trees are likely to grow out and away from the trunk on trees planted into field soil (Hewitt and Watson 2009), because there is no container wall to deflect them back over the flare. An- other contributing factor that encourages roots to grow down and away from the trunk is the soft soil common to many field nurseries. Roots growing over the flare close to the trunk from deep planted landscape-sized trees (Wells et al. 2006), may result from deflection by sides of planting holes from soil compaction (Gilman et al. 1987; Zisa 1980), which is typical of urban soils. Planting deeply into Air-Pot containers appeared to encour- age development of SGRs. The same occurred when planting deeply into Accelerator containers (Gilman et al. 2006). Worst defects were seen at the position of the #3 Air-Pot wall because deflected roots were redirected close to the trunk. Despite more defects associated with deeper planting, serious defects occurred even at the shallow planting depths for all three species tested. For example, an average of 59.9% of the trunk was wrapped with SGRs greater than 5 mm diameter on maple planted shal- low into #3 containers (Table 2), and 346 cm of roots greater than 5 mm diameter were growing over the flare. Both condi- tions could lead to health problems later (Wells et al. 2006). Root defects should be removed (by pruning) each time the tree is potted to a larger size, even when trees are planted at the ap- propriate depth in the container. This has been shown to dramati- cally reduce defects (Gilman et al. 2006; Gilman et al. 2010b). Most defects were hidden from view because they were found below substrate surface; and presence of a visible root flare was not related to occurrence of root defects (Table 3). Once substrate was removed, defects were clearly visible (Figure 1). Root balls on elm and maple were packed with roots growing in many dif- 137 ferent directions which made it time consuming to remove sub- strate and roots above root flare. This could have been magnified by retaining trees in #3 Air-Pot containers for a longer period of time; they were only in for seven months, in this study. More than a few growers (Todd Gentry, pers. comm.) leave trees in this container size for longer. Arborists and others charged with planting trees in this condition will find it time consum- ing to remove these roots on elm and maple prior to planting. CONCLUSIONS Growers exercising care to position the liner root ball so the top-most root is close to the substrate surface will produce bet- ter quality trees than those planting deeper (Figure 2). It ap- pears more problematic to plant deeply into a #15 container than into a #3 container size. Lack of root flare was a good indication that trees were planted too deeply into the #15 con- tainer size. Based on results from this study, rooted cuttings of red maple should be positioned so the point where the top-most root emerges from the trunk is within 6 cm of substrate surface. Magnolia should be positioned as high as possible in the sub- strate profile because, unlike ‘Florida Flame’ red maple and Cathedral Oak (Gilman et al. 2006), magnolia roots generally did not grow from the buried portion of the stem. This placed the root flare below many deflected roots which grew over and crossed the flare tangent to the trunk. Allée elm should be posi- tioned as high in the substrate profile as possible to reduce inci- dence of SGRs which developed when liners were planted deeply into #3. Root ball surface of #3 and larger containers should be planted so the point where the top-most main root emerges from the trunk is either at or just below substrate surface. Substrate on the surface along with roots growing over the flare may have to be removed when shifting to a larger container size or into field or landscape soil in order to produce quality root systems. Growers of container trees can exercise some control over for- mation of root defects by planting at the appropriate depth; howev- er, even planting shallow at three shifts to larger containers resulted in serious root defects for many trees, especially red maples. Land- scape contractors, horticulturists, and arborists also share in the responsibility for helping develop and maintain healthy root sys- tems by instituting root management programs as part of planting and routine maintenance. This strategy could be incorporated into bid specifications. Root systems should be inspected by washing substrate from the surface in order to check for and treat defects. Acknowledgments: Thanks to www.GreatSouthernTreeConference.org., TREE Fund, and Florida Nursery, Growers and Landscape Association for partial funding of this research. LITERATURE CITED Anonymous. 1998. Florida Grades and Standards for Nursery Stock. Florida Department of Agriculture and Consumer Services, Div. of Plant Industry, Gainesville, FL. Balisky, A.C., P. Salonius, C. Walli, and D. Brinkman. 1995. Seedling roots and forest floor: Misplaced and neglected aspects of British Co- lumbia’s reforestation effort? The Forestry Chronicle 71:59–65. Browne, C., and K. Tilt. 1992. Effects of planting depth on three orna- mental trees. Proceedings Southern Nurseryman Association 37:2–4. ©2010 International Society of Arboriculture
May 2010
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
