Amounts of backfill and mulch around and over root balls of trees and shrubs may ensure or hinder passage of air and water to roots. Edward F. Gilman, University of FL Professor, and Laura Sadowski, Information Specialist, FL Institute of Food and Agricultural Sciences, in Planting and Establishing Trees, Ch. 11, September 2007, state on p. 1, “Planting and establishing trees is all about managing air and moisture in the soil. Manage these correctly and trees will grow quickly following planting.”
Barbara Leach, Horticultural Associate, Agriculture and Natural Resources, Virginia Cooperative Extension, made use of Gilman and Sadowski’s material while presenting a recent workshop in Roanoke, VA. Leach stressed removal of synthetic protective material as well as amounts and types of backfill needed to ensure quality tree and shrub root growth. She also presented specific instructions on mulch placement.
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Material that will not decompose in soil – string, rope, strapping plastic and synthetic burlap – should be removed. Beware, some synthetic burlap looks much like the natural. Synthetic burlap melts when lit; natural burlap flares and burns to ash.
Some contractors leave not only natural burlap – flipped over and exposing roots at the top of the root ball – but also wire baskets in place. Others remove the baskets, being careful to avoid shifting the root ball. Gilman and Sadowski state on p.4 of Planting and Establishing Trees, Ch. 11 that “There is no research documenting the detrimental effects of wire baskets on trees.” Contractors who decide to remove the baskets should do so after the tree placement in the planting hole, and then stake the tree to stabilize it.
Soil, originally removed from the planting hole, makes the best backfill. Research and experience show that soil amendments – peat moss, compost or humus – are not necessary.
Contractors should loosely position backfill in the planting hole. When this step is complete, the root ball with topmost roots exposed should be above the line of surrounding landscape soil – 1 inch for small plants to 3 inches for large trees. (Photo #1)
Slice down with shovel into backfill soil to break up large soil clumps. Step firmly on backfill in the planting hole to secure the root ball. Add water – as much as 10 to 20 gallons for a large specimen – and more backfill to eliminate depressions and holes. However, do not pack soil because this action eliminates important small air pockets.
Apply about 3 inches of mulch around the plant beyond the root ball – estimate a 2- to 3-foot diameter circle for each inch of tree trunk diameter. Provide only a thin mulch layer – no more than 1 inch – over the root ball for aesthetics. Too much mulch over the root ball cuts off oxygen and water penetration. (Photo #2) Never pile mulch, volcano-fashion, (Photo #3) against the plant stems or trunk. This causes feeder roots to grow into the mulch layer as well as encourages stem-girdling roots to form in some trees.
Stake young trees to allow trunk growth, and older trees to hold root ball in place. Investigate and select a proper staking system for the project.
It is not necessary to prune top growth to compensate for root-loss. Prune top only to remove broken branches or branches that might compete with the main leader.
Gilman, Professor Edward F., Department of Environmental Horticulture; University of Florida and Laura Sadowski, Information Specialist, Institute of Food and Agricultural Sciences, Gainesville. Planting and Establishing Trees, Chapter 11, Publication ENH 1061, original publication date September 2007, Urban Forest Hurricane Recovery Program series of the School of Forest Resources and Conservation and the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
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