A gardener’s guide to fall planting of deciduous trees

Posted Aug. 26, 2011, at 7:05 p.m.

Is it too late to plant a deciduous tree? In short, no. Fall planting can help deciduous trees replace the absorbing roots that were lost during harvest and handling in the nursery as well as roots lost during planting.

Deciduous trees planted in spring must establish a new root system while supplying emerging leaves with water and nutrients. Fall planting, on the other hand, provides time for development of new roots after the leaves have dropped. Many tree species, such as sugar maple, continue producing new roots until the soil freezes. A tree planted in September may have six or more weeks of new root development before winter closes in.

To ensure long-term success with your fall-planted tree, follow these guidelines: Purchase a small tree, one to two inches in trunk diameter. Small trees establish adequate root systems more rapidly than large trees and ultimately catch up in trunk diameter with initially larger trees.

Your new tree should show an obvious trunk flare, a widening of the trunk as it approaches the soil surface. Soil is often piled around the trunk during harvesting and handling of ball-and-burlap trees, so before planting a ball-and-burlap tree, completely remove the burlap and this excess soil until you can see the trunk flare. Better still, ask to do this in the nursery or garden center before you purchase the tree.

Avoid purchasing a container-grown tree that does not show an obvious trunk flare. It may have been planted too deep in its pot, a situation that can lead to tree decline in the future.

Once home with your new tree, dig the planting hole at least twice as wide as the tree’s root ball. Do not dig it deeper than the root ball; the loosened soil under the tree will settle and so will the tree.

Do not amend the backfill soil with organic matter; use only the native soil that came out of the hole. The only exception is when the native soil is almost totally sand or clay, when up to 25 percent by volume of compost should be added to the backfill.

Before placing your tree in its new home, carefully tease any roots circling the root ball to an outward growing direction. Then center the tree in the hole, spreading the roots outward and making sure that the base of the trunk flare will be at the soil level when you finish planting.

Do not stomp on the soil as you return it to the hole! This breaks or damages tree roots.

Instead, settle the soil with water. Once the hole is half full of soil, gently add water to settle the soil around the roots, eliminating air pockets. Water again after the hole is completely filled.

Mulch with compost at least out to the drip line, starting a few inches from the trunk. Do not pile mulch at the base of the trunk! This all-too-common form of mulching is appropriately called “volcano mulching” — the tree looks like it is erupting from a volcano. Moisture becomes trapped within the trunk-mulch interface resulting in bark rot and slow death of the tree.

Minimize pruning at planting. Healthy root growth next spring depends on chemicals transported from an abundance of leaves to the roots. When planting in the fall, remove only dead, damaged and diseased branches, delaying other pruning until after the establishment period (one year for each inch of trunk diameter).

Do not fertilize your newly planted tree. In fact, ask yourself, who fertilizes trees in the forest?

Somewhere along the way — I have to think this was the work of fertilizer-industry advertising — homeowners were led to believe that trees in the garden must be annually fertilized for good health and adequate growth. Nothing could be further from the truth.

Research has shown that pushing tree growth with nitrogen leads to reduction in tissue defense chemicals, the chemicals responsible for insect herbivore and disease resistance. In other words, excess nitrogen increases insect and disease problems. When a tree receives a heavy shot of nitrogen in the form of applied fertilizer, it shifts its metabolism toward growth at the expense of defense chemical production. Insect herbivores, such as the Japanese beetle, love nitrogen-rich tissues and so herbivory increases while the tree’s ability to build up herbivore-deterring chemicals decreases. A similar scenario has been established between high levels of nitrogen and disease pathogens.

When soil nitrogen levels are relatively low, metabolism favors defense chemical production over growth. And this is where we want our trees to be, growing relatively slow in response to relatively low soil nitrogen levels. In fact, trees fed annually by mulching with compost receive all the nitrogen necessary for a modest rate of growth. These trees will also be healthier, less damaged by herbivores and pathogens.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

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