Pruning Landscape Trees

What Is Pruning?

Pruning is the purposeful removal of plant parts. Its use is preferred to less precise terms like trimming. This fact sheet deals mainly with pruning of branches on ornamental trees. It does not cover pruning of fruit trees for fruit production, shearing or other intensive crown shaping practices, or root pruning.

Why Prune? Reasons for pruning landscape trees generally fit into three closely-related categories: health, hazard, and form. Step back and reconsider if you find yourself pruning off healthy, non-hazardous branches on a tree with good form. Health — Pruning for tree health includes removal of insect or disease infested branches, broken or dead branches, crowded branches, and branches or portions of trunks with included bark. Pruning to "open-up" a tree's crown to encourage light penetration or air movement generally is not needed. Hazard — Pruning to reduce hazard to people or property includes removal of dead and decaying branches; branches that interfere with sight lines or travel along streets, driveways, or sidewalks; branches that rub against structures; thorny or spiny branches that might cause injury, and pruning for utility line clearance. Healthy, strong, properly attached branches that overhang a building do not usually pose an unreasonable safety risk and do not necessarily need to be removed. Form — Pruning for tree form or shape involves removal of certain branches and leaving others to direct growth toward and away from certain areas. Pollarding, crown raising, and topiary all are examples of pruning for form.

When to Prune Time of Year — Pruning can be done at any time of year with special care and knowledge, but certain times are better than others. Pruning is best done in winter or early spring before buds swell when tree energy reserves are high and the tree is dormant. Though certain trees, such as birches, maples, and walnuts, may exude sap or "bleed" when pruned at this time of year, this is not a problem and stops within a few days. During the spring growth period bark is tender and easily damaged and pruning must be done very carefully. In fall pruning wounds may be more easily infected with decay microorganisms. Though summer pruning can be done, considerable dieback may occur at the edges of summer pruning wounds, possibly due to drying of the living tissues at wound edges. Quickly wrapping such wounds with white plastic sheeting can reduce this dieback (see page 4). Time of Life — At planting time only prune branches that are dead, broken, or that have insect or disease problems. Otherwise, prune early in a branch or tree's life to avoid pruning large branches or letting serious problems develop. For maintenance pruning on established trees try to prune branches before they exceed 2 inches in diameter.