Pruning is a horticultural practice that alters the form and growth of a plant. Pruning can also be considered preventive maintenance. Many problems may be prevented by pruning correctly during the formative years of a tree or shrub.

Reasons for pruning

Prune to promote plant health

• Remove dead or dying branches injured by disease, insect infestations, storms or mechanical damage. Such damaged wood can and should be removed as soon as possible. Remove branches that rub together. Remove branch stubs that can be entry points for insects and disease.

Prune to maintain plants’ intended purpose

• To encourage flower and fruit development and to maintain a desired plant form

Prune to improve plant appearance

• For most landscapes, a plant’s natural form is best. When plants are properly pruned, it should be difficult to see that they have been pruned.

Prune to protect people and property

• Take down hazardous trees and prune out weak or narrow-angled tree branches that overhang homes, sidewalks and anyplace they could injure people or damage property. Prune branches that obscure vision at intersections. And for security purposes, prune shrubs or tree branches that obscure the entrance to your home.

When should pruning start?

• Pruning begins at planting time. When planting young trees, remove only diseased, dead or broken branches. Begin training a plant in the dormant season following planting. At that time, begin pruning to shape, remove crossing branches and branches that grow back toward the center. Remove branches that are spaced too closely on the trunk.

Pruning large, established trees

This is a job best left to qualified tree professionals who have the proper equipment. You may be asked to choose between several types of tree pruning.

• Crown thinning is the selective removal of branches on young trees to promote better air circulation and light penetration. Use it cautiously on mature trees.

• Crown raising is done to allow more clearance above lawns, sidewalks, streets, etc.

• Crown reduction is the removal of larger branches at the top of a tree to reduce its height. Done properly, it’s different from “topping,” because branches are removed immediately above lateral branches, leaving no stubs. Crown reduction is the least desirable pruning practice and should be done only when absolutely necessary.

A few cautions

• “Topping” of trees is not recommended. Removing large branches by leaving stubs can cause several health problems. It also permanently destroys the tree’s natural shape and promotes suckering and development of weak branching.

• Never remove more than one quarter of a tree’s crown during a single season.

Proper branch pruning

• To shorten a branch, cut it back to a side branch or about one-quarter inch above a bud. Always prune above a bud facing the outside of a plant to force growth in that direction.

• To remove large branches, three or four cuts will be necessary to avoid tearing the bark. Make the first cut about 18 inches from the trunk on the underside of the branch, one-third to halfway through the branch. Make the second cut on the topside, about an inch farther out on the branch, and cut until the branch breaks. The final cut should be made so that the branch collar (swelling around the branch where it meets the trunk) is undamaged. The wound will heal more effectively. Make the final cut just beyond the collar, but don’t leave a stub.

When to prune

The late dormant season (about February and early March in this area) is best for most pruning, with the exception of spring-flowering trees and shrubs.

• Without the foliage, it’s easier to see the tree’s structure and where to make the cuts. The limbs are also lighter and easier to handle.

• There’s less chance of transmitting diseases from one plant to another through pruning.

• Insect activity is low, so there’s less chance of exposing oaks to oak wilt disease. It’s spread by beetles carrying the oak wilt fungus, which are attracted to the open wound. Trees in the red oak family can be killed within months of infection, while white oaks may linger on for several years.

• Wounds will start to heal rapidly with the start of spring growth.

Have a question? In Washington County, call the Master Gardeners office at 724-228-6881. Follow us on Facebook. Also consult the Penn State Extension website at http://extension.psu.edu/plants/master-gardener/counties/washington for additional information.

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