University of Wisconsin - Extension

Trees are the most valuable of our landscape plants. Care for them properly, and your trees will live a long and healthy life. Start tree maintenance the day you plant the tree and continue throughout its life.

"Proper pruning does help trees live longer," said Mike Maddox, University of Wisconsin-Extension Dane County commercial horticulture educator. "It keeps your trees attractive, healthy and less susceptible to injury from natural forces such as severe storms. On the other hand, poor pruning practices, such as topping, make trees less attractive, more prone to pest and weather problems and can actually shorten their life span."

For pruning medium and large trees, you may want to hire an arborist -- a trained tree service professional, according to Maddox. These trees deserve professional maintenance because of their landscape value. By having a professional prune your larger trees, you can also avoid injuring yourself or damaging the tree, nearby buildings, utility wires or other landscape plants. Contact your UW-Extension county horticulture agent for more information on hiring an arborist.

If you plan to prune smaller trees, Maddox offers a few helpful tips:

First, use the right tools. You can prune most shrubs and small trees with a hand pruning shears, a lopping shears and a hand pruning saw. Pruning tools are available at garden and hardware stores and through garden supply catalogs.

Most deciduous trees should be pruned in late fall to winter. Late fall or winter pruning is especially important for oak trees to help prevent the spread of the fungus that causes oak wilt. Avoid pruning in late spring and summer when disease pathogens are active and wounds close more slowly.

Some trees, like maple and birch, will bleed when you prune them in early spring. This heavy sap flow does not hurt the tree. Pruning wounds are best left unpainted. Tree wound treatments are not recommended for most pruning cuts. One exception is that oaks pruned during the growing season must have wounds treated to keep insects out that transmit the oak wilt fungus.

Newly planted trees should not be pruned unless a branch is broken, diseased or dead. Young trees can be pruned to encourage a well-branched canopy. Older, established trees, if properly pruned when young, will require little pruning. Never "top" a tree, as this leads to poor branch structure and makes limbs vulnerable to breaking.

When pruning trees, there are several types of branches to remove. Prune out dead branches whenever you see them. Remove broken or diseased branches and remove the weaker of two branches that are rubbing together. Finally, prune out watersprouts and suckers. Suckers are long straight shoots that grow out of the ground from the tree's roots, usually occurring at the base of the trunk. Watersprouts are long straight shoots that grow off the trunk and main branches.

Certain trees have multiple leaders, including maples, ash and lindens. Trees grow best, and develop a better branch structure, when you train them to a single leader. It's important to remove all but the strongest leader early in the life of trees that are prone to developing multiple leaders.

Occasionally, you may need to remove lower branches on mature trees. Because these branches are often large, it's best to use the three-cut pruning method for removal. To do this, make an undercut halfway through the branch, a foot out from the trunk. Make a second cut on the top side of the branch, a few inches beyond the undercut. You'll remove the branch with this second cut. Finally, remove the stub with your third cut. The three-cut method prevents the falling branch from tearing a large section of bark from the trunk.

No matter what kind of branch you're pruning, the cardinal rules of pruning are to never leave a stub and never make a flush cut. Stubs are unattractive, do not heal over and can result in decay moving into the tree. Cuts made flush to the trunk result in large wounds, which take a long time to close. Make pruning cuts just beyond the branch collar. Collars are natural swellings that occur where the branch attaches to a larger limb or to the trunk of the tree.

There are several UW-Extension publications on pruning trees and shrubs. Contact your UW-Extension county horticulture agent for more information, or visit the web site of the UW-Extension Urban Agriculture/Horticulture Team at http://www.uwex.edu/ces/wihort/landscape/ .