Pruning is one of those gardening topics that has an air of mystery about it. When to prune trees? Why do you prune trees? How do you prune trees? Curious gardeners want to know. Here are the basics.
When to prune trees? February and March are generally considered the best time to prune trees in the North. The weather is still cool enough that the trees are in their dormant state and they will have time to repair any wounds during the spring. Given our erratic springs of the past few years, it might be best not to wait too long to do pruning. A warmish, sunny day is ideal pruning weather.
Why prune trees? The goal of pruning is to keep your trees healthy and shapely, to promote flowering or fruit, and to keep your neighbors safe from falling branches, obstructed views and other hazards.
How to prune? That depends on the tree. (Flowering shrubs, such as lilacs, should be pruned after flowering.) Generally, the first step in all pruning is to remove any potential problems. Called the three Ds, you should first get rid of all dead, diseased or damaged branches. You also will want to remove branches that are criss-crossing each other or rubbing together, stray stubs on the tree from past pruning and “water spouts,” those branches that come up from the base of the tree. If you are going for a longer trunk, you may want to remove branches below a certain level.
After that, the goal is to give the tree its proper shape. Consider where the main branches should be and what the tree’s natural shape is — a vase, upright, or spreading. The University of Minnesota Extension Service has a great fact sheet with drawings on where to make cuts and how. Overall, you do not want to cut more than about one-third out of a tree you are pruning. And, it’s not a good idea — for either health or aesthetics — to “top” a tree. Topping involves cutting branches from the top, like you are giving it a haircut.
A few warnings: Never prune near electrical or utility lines. Let your city know if trees need pruning near power lines. Be aware of your own limits. I prune all of my smaller trees myself using several types of bypass pruners and a pruning saw. For trees that require tall ladders and have large branches, I call in a pro.
—Mary Lahr Schier