Home & Garden

Want healthy, long-lasting trees in your yard? Here’s what not to do

Trees can be affected by the actions of homeowners, including construction activity, improper use of home and garden equipment, de-icing salt, soil compaction, improper pruning and improper use of pesticides.
Trees can be affected by the actions of homeowners, including construction activity, improper use of home and garden equipment, de-icing salt, soil compaction, improper pruning and improper use of pesticides. TNS photo

Two years ago we purchased some good size trees from Wheatfield Nursery and had them plant them. They are doing great and have added a lot to the overall appearance of the property. As I looked at them the other day it got me to thinking that we do not really talk about trees and how they can be affected by what we do as homeowners.

There are many factors that can relate to poor growth, quality and survival of trees in our landscape. Many of the problems can be traced back to people. Some of the ones that come readily to mind are construction activity, improper use of home and garden equipment, de-icing salt, soil compaction, improper pruning and planting (girdling roots) and improper use of pesticides. Some symptoms of overall tree decline include: small and discolored leaves, premature fall coloration and loss of leaves, reduced twig growth, dying twigs in the upper crown and decline of all parts of the tree.

Construction activity around trees is one of the most common sources injury caused by people. Soil compression caused by heavy equipment can physically damage roots and destroy the root environment by reducing the soil aeration. Since soil compression is often difficult to reverse, it is best to prevent heavy traffic over an area filled with tree roots.

Excavation near trees will also destroy many of the roots. Contrary to popular belief, root injury — not trunk injury — during construction is most likely to be fatal to trees. Covering tree roots with additional soil, asphalt or concrete during construction alters the amount of water and air available to the roots. Trees with covered roots may die within three to five years. If light-textured material has been used, the process may take as long as 10 to 15 years. Both of the above problems can be readily observed on the Penn State campus, although they try to avoid injuring the trees.

Home and garden equipment can injure trees. Injury occurs when you hit trunks roots and branches with mowers, tiller, pruners and snowplows. For example, over the course of a season, repeated impacts from the sharp edge of a lawnmower will girdle the trunk of a tree. I have observed serious canker formation on the lower trunks of dogwood and other trees at heights equal to the edge of a mower. String-line trimmers also cause problems for trees.

Removing the sod near tree trunks will eliminate the need to mow close. A mulch on this exposed soil will help retain moisture and prevent weed growth while protecting the trunk.

De-icing salts used on walks or roads are toxic to plants. Injury is possible to all parts of the plant. These salts will penetrate to the root system even though the soil is frozen in winter. Trees near salted areas tend to be more susceptible to drought injury because they are already under stress. You can see the injury to trees and shrubs at the seashore after a dry nor’easter when the salt from the ocean spray is carried inland.

Agricultural chemicals — especially herbicides or weed killers — can cause serious problems with trees, most often because of the common misconception that “if a little is good, a lot will be better.” Proper use of any pesticide includes strict adherence to recommendations given on the label.

Herbicides mixed with turf fertilizer for weed control in lawns can cause injury when such combinations are used to close to trees or heavy rains wash them into the root zone of trees and shrubs. Read the label to determine just how close the material can be applied to woody plants.

Pruning trees helps by removing diseased, dying or injured tissue, but it can increase the chances of disease and decay if done improperly. When pruning, make all cuts close to the main branch or trunk, although not so close that the slight flare at the branch’s base is removed. Retaining this flare improves the healing of the wound. Tree wound dressings are no longer recommended. Dying branches should be promptly removed.

Improper planting also places trees under stress. It may not cause immediate loss, but it can result in a gradual decline over a number of years. Proper planting makes the transition from the nursery to the site easier for a tree and increases its chance of surviving. Poor root placement in the hole, improper planting depth, poor quality backfill soil and dry soil are factors that inhibit the tree’s growth. Failure to remove the newer types of synthetic burlap after planting retards root expansion. Research has also found that the wire baskets planted with some trees caused root restriction. These too should be removed at planting time.

So as you can see many things that may negatively impact the growth of your trees in the landscape may be caused by you.

Bill Lamont is a professor emeritus in the department of plant science at Penn State and can be reached by e-mail: wlamont@psu.edu.
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