Accidents happen in the yard or garden and trees get wounded, often by a lawn mower or weed whacker that gets too close. What’s the best way to help the tree? In most cases, the answer is to let the tree repair the wound on its own.
Upon being wounded, trees begin a natural process of callusing over the wounded area with new bark and wood. In the spring, when trees are growing vigorously, this process will naturally occur quickly. During other times of the year when growth is not as vigorous, try to keep wounded trees growing as vigorously as possible by fertilizing and watering.
On some trees, however, a wound made during the active growing season may attract insects and pass on pathogens. Wounds on oaks and elms, for instance, may attract borers and beetles that are carriers of diseases such as Dutch elm disease and oak wilt.
In such cases, a petroleum-based tree wound dressing may be applied to cover the freshly cut wood in order to inhibit decay or insect infestation, but its effectiveness is debatable. Researchers at Washington State University have found that wound dressings do not prevent entrance of decay organisms or stop rot from occurring.
They do, on the other hand, seal in moisture and decay, and sometimes serve as a food source for pathogens, prevent wound wood from forming, inhibit compartmentalization, and eventually crack, exposing the tree to pathogens.
When pruning a disease-prone species while insects or fungi are active (that is, during the warmer times of the year), a light coating of an insecticide or fungicide may be warranted. Otherwise, avoiding wounds is the best practice.
Mulch around trees and shrubs to avoid mowers and weed whackers getting close to trees, and prune during the dormant season when insects and pathogens are not active.