Gilman, E.F., M. Paz and C. Harchick

Nursery planting depth, mulch application, and root pruning at landscape planting affect tree health and anchorage

Arboriculture & Urban Forestry 41 (2): 75-87

Influence of root collar depth in a nursery root ball and potential root remediation when planting into the landscape are subject of increasing research. Mulch placement on root ball surface at planting has also been called into question recently. Trees planted deeply in nursery containers required ≥41 percent more time to remove substrate and roots growing over the root collar at planting than trees planted shallowly. Circling roots on trees planted from 170 L containers persisted for five growing seasons after planting into the landscape unless remediated by pruning at planting. Root remediation improved Ulmus and Acer root systems by dramatically reducing percent trunk circled with roots without influencing post-planting xylem potential, crown growth, or anchorage during the first five years after landscape planting. Mulch placed on the root ball surface caused more regrowth of circling roots on Acer - but not Ulmus - following root remediation. Bending stress to tilt trunks was most correlated with cross-sectional area of leeward and straight roots on Ulmus or windward and straight roots on Acer. The initial increase with time in bending stress required to tilt trunks after planting followed by a drop in bending stress suggests that trees planted from nursery containers could be more susceptible to uprooting in a wind storm as they became established beyond three or four years.