Assessment of Rootball Planting Treatments of Two Species of Container-grown Trees

Researchers have done extensive work assessing planting techniques for container-grown trees. The results are often very specific to species and soil type, so it is hard to make broad recommendations. We implemented a study to assess the differences in establishment success and growth of two different species of container-grown trees. We were interested in determining if different handling methods had an effect on establishment and growth of the trees, and what role site preparation plays during planting. To accomplish this, we selected Acer rubrum 'Brandywine' and Nyssa sylvatica 'Wildfire'. A. rubrum have very fibrous roots, while N. sylvatica have more woody root systems. Fifteen-gallon trees were placed in the hole with no rootball treatment, had the outer edges of the rootball shaved off two inches, or the rootball was thrashed with the sharp edge of a shovel. Soil treatments included a site preparation treatment, where composted leaves were added, and a no site preparation area. Growth measurements included caliper at 6” above rootball, height, and twig extension. After two years a third of the 120 trees were destructively harvested. Leaves and stems smaller than one-inch diameter were separated from larger branches and the trunk. These were oven-dried to obtain biomass dry weight. Roots were harvested using a 42”-tree spade and all soil was removed with either water or an air spade. We hung the rootballs and marked the original rootball diameter in the 15-gallon container. We separated roots into various size categories and recorded the number of each. In addition, we indicated if the roots came straight out from the rootball, girdled the trunk, or circled around the rootball. We found there was no significant difference in aboveground biomass growth. However, there was a significant difference in root architecture. Trees we placed in the holes with no treatment had the most trunk girdling and circling roots, and tended to be larger diameter. Those that were shaved or thrashed had fewer and smaller diameter circling or girdling roots. Roots will be oven-dried and weighed. We believe we will find significant differences between the rootball treatments. The study will continue through May, so at present we can offer no recommendations on best handling practices for container-grown trees. We expect to have results and recommendations available by the August ASHS meeting.