Effects of Root Pruning on Container-Grown Maple and Oak

Abstract

Two experiments were conducted on container-grown plants that were actively growing in spring to evaluate the effects of root pruning prior to repotting or planting in a field plot. In experiment 1, severe root pruning significantly reduced height and trunk diameter growth for both ‘Summer Red’ maple (Acer rubrum L) and overcup oak (Quercus lyrata Walt.) after repotting into a larger container. Shoot and root dry weights were less with plants severely root pruned compared to plants that were not root pruned or had been lightly root pruned. Overcup oaks that received no root pruning or were lightly root pruned did not differ in height or trunk growth 24 weeks after study initiation. However, overcup oaks severely root pruned had brown foliage within 10 days of repotting and within 2 months had extensive dieback, which resulted in negative height growth by the end of the study. In experiment 2, ‘Autumn Flame’ red maple that received no root pruning had similar growth to plants that had light root pruning, but was greater than plants that received moderate or severe root pruning during the first growing season in the field. Autumn Flame red maples severely root pruned prior to field planting had 65% less height growth than plants receiving no root pruning during year 1. After four years, shoot and trunk diameter growth was similar among treatments. The number of circling roots at the soil surface decreased as the amount of root pruning increased.