Is it time to prune trees and shrubs?

By Gary Johnson, University of Minnesota Extension

ST. PAUL, Minn. (4/7/2008) — As the winter’s snow melts away, spring chores and promises slowly take shape and gardeners begin sharpening and oiling their pruning tools. Is late winter and early spring the best time to prune trees and shrubs? Well, it depends.

If the urge to prune is the reason for pruning, suppress that urge! Unnecessary pruning unnecessarily stresses trees and shrubs during an already stressful time of the year, can reduce or eliminate the beautiful flowers that should have decorated the plant in the spring, and can ruin the tree or shrub’s natural form.

When is pruning necessary? There are some very good reasons to prune, and they generally fall into one of these four categories:

Canopy cleaning. Whether tree or shrub, as a plant gets older some of the branches die. Removal of these branches improves the appearance of the plant and, in the case of trees, makes it safer to walk under them.

Maintaining hedges. Late winter is the best time to develop the ideal hedge shape: broad at the bottom, narrower at the top. There’s little to no foliage to dispose of and if an expert job isn’t done, within a month or two the new leaves will cover all of the pruning errors.

Flower and/or fruit production. As some shrubs get older, they become less “flower productive.” Stimulating new stems (canes) usually stimulates better flower production.

Removal of weak branches. Winter is a perfect time to find those “weak links” and remove them before the weight of summer leaves or a storm rips the tree apart.

Here are some basic guidelines for pruning:

• For shrubs that normally flower before mid-June, prune them AFTER the flowering is done. Spring pruning removes all or most of the flower buds for that season.

• If oak wilt is present, avoid pruning oaks in the high risk season (April, May and June). Winter is the best season to avoid contracting oak wilt.       

• Don’t over-prune mature trees. Do not remove excessive amounts of living branches (keep it less than 25 percent of the living tree). The branches produce the leaves that trees depend on.

• Mammals bleed, trees lose sap. If maples or birches need to be pruned, prune them and don’t believe the “bleeding tree” myth.
  

Any use of this article must include the byline or following credit line:
Gary Johnson is a forest resources educator with University of Minnesota Extension.

NOTE: News releases were current as of the date of issue. If you have a question on older releases, use the news release search (upper left-hand column of the News main page) or the main Extension search (upper right of this page) to locate more recent information.