Mulch and Root-ball Manipulation Affect Establishment of Container-grown London Planetrees

Landscape contractors and urban foresters are increasingly using container-grown shade trees for tree planting projects.  Establishment of container-grown trees, however, may present unique challenges compared to traditional balled-in-burlap trees.  In this project we conducted two experiments to examine growth and physiological responses of London planetrees (Platanus × acerifolia ‘Bloodgood’) following transplanting.  In the first experiment we planted 48 planetrees, from #25 containers, in 3×2 factorial combination of root-ball manipulation (‘control’ – no treatment; ‘shaved’ – outer 3 cm of roots removed; or ‘teased’ – outer circling roots teased apart) and fertilization (no fertilizer or 400 g of controlled release fertilizer (15-9-12:N-P2O5-K2O, 5-6 mo. release)).  In the second experiment 48 planetrees from #25 containers were planted in a 3×2 factorial of root-ball manipulation and mulch (no mulch or 8 cm of ground pine park mulch).  Fertilization did not increase height or caliper growth after two years (p>0.05) but increased (p<0.05) leaf SPAD chlorophyll index.  Both root-ball treatments increased new root growth relative to the control. Shaving the root-ball increased new root growth by 67% compared to the control trees; whereas teasing apart the root-ball increased new root growth by 49% relative to control.  Mulching consistently increased soil moisture at 0-15 cm and 0-45 cm depth and increased tree caliper and height growth.  The results indicate that root-ball manipulation at planting can enhance new root growth.  Mulching greatly improved soil moisture availability and growth after transplanting, whereas fertilization had only a modest impact on post-transplanting tree performance.