Choose the right plants, make small cuts and clean your tools for best results.
The best time to prune is at the beginning or end of winter, when trees and shrubs are dormant but it's warm enough to work outside. But sometimes you just don't get it done. Then spring rolls around and there's so much to do that pruning takes a back seat. Before you know it, summer's here.
If you're one of the many gardeners who's put off pruning until now, you're in luck. Late summer is considered the second best time to prune. In fact, in a few cases, it's even a better time than winter.
What to prune now
Some trees and shrubs bloom on shoots that sprouted this year (called new wood), and some bloom only on wood that was produced last year (old wood).
Plants that only bloom on old wood -- spirea, weigela, big leaf and oak leaf hydrangea, lilacs and others -- should be pruned right after they bloom. That way, you'll get the best possible bloom next year.
Also, if you have a tree or shrub with a badly damaged or dead limb, prune that limb now. If you leave it, it's likely to fall off the tree and leave a large wound behind. That wound could create an entry point for diseases. Pruning cuts, on the other hand, are much cleaner, which makes it less likely an infection will occur.
Wait to prune
In summer, there are more diseases floating around than in winter, especially if it's been a wet summer. Some trees and shrubs are more susceptible to attack by a wide variety of diseases. So it's best to wait until winter to prune oak, honey locust and ash trees as well as fruit trees, such as apples and plums.
Also avoid pruning young or weak trees and shrubs. Pruning removes not only limbs and branches, but also leaves, which help create food for the plant. While most trees and shrubs can easily handle that loss, unestablished trees and those stressed by drought or disease may suffer slowed growth. When in doubt, wait until winter.
How to prune
When pruning in warm weather, always make the smallest cuts possible. Be sure to use a pruning saw or sharp pruners and be sure to sterilize them before and after you prune each tree or shrub. To sterilize, just dip your tools into a can of ethanol. Household products such as Lysol also will work. Keeping your tools clean is especially important in summer because dirty tools can easily transfer diseases.
What to avoid
After pruning, it's natural to want to cover the wound to prevent disease. Don't do it. Using pruning tars and paints only slows the healing process
Jeff Gillman, an associate professor of horticulture at the University of Minnesota, is the author of several gardening books.