The old practice of pruning tree branches was to cut flush with the tree trunk. When this is done the ability of the tree to stop decay is greatly decreased. While the tree will still form a barrier zone, it is a very weak barrier and decay organisms can infect the main trunk of the tree. The current recommendation is to prune the branch to just outside the collar. Properly pruned branches will heal all around the wound, not just from the sides. Callus that forms around a pruning cut should have a ring or donut shape if the branch was properly removed. If the callus is elongated or oval shaped, the branch may have been cut to close to the trunk.

For years people have applied a wound dressing to pruning cuts to block out microorganisms, keep moisture in or out, and speed the healing process. However, research has shown that treated wounds do not heal quicker than untreated wounds. In most cases, sealed wounds actually give wood inhabiting microorganisms an environment favorable for growth and decay development. Some wound dressings kill cambial cells and cause the wound to remain open for years longer than if no treatment had been applied.

When to Prune
Pruning and training should start when trees are quite young. This will prevent many serious problems before they develop. Older, neglected trees are more difficulty, dangerous, and expensive to prune. Most of the pruning on older trees should be done when they are dormant; there is less weight on the limbs. It is also easier to see the framework of the branches. Pruning of young trees should be done when problems can be observed.

Some trees, such as birch, honey locust, maple, dogwood, elm, and walnut exude excessive sap from the wound when pruned in late winter or early spring. While this bleeding does not hurt the tree it can be alarming to many gardeners. These trees will not bleed if pruned in late spring, summer, or fall.

The time of pruning should take into account the life cycle of insects and diseases. Plants in the genus Prunus are prone to develop bacterial cankers. The spores for the diseases, which are released in fall and early winter, can enter plants through fresh pruning cuts and wounds. Prunus trees do not initiate new cankers during late spring or summer. Dogwood borers are most active in May, June, and July. Pruning cuts should not be made during these months.

Prepared by: Erv Evans, Consumer Horticulturist, NC State University

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