Proper Pruning of Trees

The late dormant period (February to early April) is an excellent time to prune deciduous trees. The absence of foliage at this time of year gives the home gardener a clear view of the tree and allows him/her to select and remove appropriate branches. Also, the "healing" processes (wound compartmentalization and callus formation) occur most rapidly just prior to the onset of growth in spring. Proper pruning improves the appearance, maintains the health, and prolongs the life of trees. Improper pruning destroys their natural beauty, weakens them, and may lead to their premature death.

It is essential to make proper cuts when pruning trees. Do not make flush cuts. Flush cuts are cuts made as close as possible to the trunk or main branch. Flush cuts produce large wounds, destroy the tree's natural mechanisms that promote healing, and slow the healing process. When pruning trees, make the final cut just beyond the branch collar and branch bark ridge. The branch collar is the swollen area at the base of the branch. The branch bark ridge is the dark, rough bark ridge that separates the branch from the main branch or trunk. Pruning just beyond the branch collar and branch bark ridge retains the tree's natural defense mechanisms and promotes the healing process. When a branch is pruned properly, a slightly raised area remains on the trunk or main branch. However, do not leave stubs.

Do not apply wound dressings to pruning cuts. The application of wound dressings or paints doesn't stop decay and may actually inhibit or delay the healing of wounds. There is one exception to the no paint recommendation. That exception involves oak trees. To reduce the risk of the spread of oak wilt, don't prune oaks from April 1 to July 1. If you must prune oaks between April 1 and July 1, for example to correct storm damage, apply a wound dressing or paint to all cut surfaces.

To prevent extensive bark damage, use the 3-cut procedure when cutting large branches. Make the first cut about 1 to 2 feet from the main branch or trunk. Cut upward and go about halfway through the branch. Make the second cut a few inches beyond the first. Cut downward completely through the branch. Make the final cut just beyond the branch collar.

Some trees, such as maple, birch, and elm, bleed heavily when pruned in late winter or early spring. However, the heavy bleeding doesn't harm the trees. (The trees won't bleed to death.) Eventually the flow of sap will slow and stop. Heavy bleeding of susceptible trees can be avoided by pruning in late June or early July.

The pruning of deciduous trees by the home gardener should be limited to small trees and the removal of smaller branches that can be reached from the ground in medium to large trees. Branches high up in large trees and those near utility lines should be left to professional arborists. Professional arborists should have the proper training and equipment to safely perform the job.

Additional information on pruning trees can be found in SUL-5 Sustainable Urban Landscapes - Pruning Trees and Shrubs.

This article originally appeared in the February 23, 2001 issue, pp. 13-14.

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