February and March Are Prime Months to Prune Woody Ornamentals

Late winter and early spring are the ideal times to prune many woody landscape plants. Trees and shrubs are still somewhat dormant, and, since air temperatures are cool, they will not respond to pruning by forcing new growth quickly that might be damaged by freezing. Also, by mid-February, the probability of extremely low temperature is much lower than in December and January, further reducing the likelihood of pruning-induced winter injury. For deciduous plants, the absence of leaves makes it much easier to see the branch structure and to select shoots that should be removed. Additionally, since spring is just around the corner, pruning cuts will callus over quickly, reducing the chance that insects and diseases will use the pruning wounds as entry points. In general, it is best to avoid pruning when the wood is frozen, since cutting frozen branches causes slightly more damage than cutting unfrozen ones. However, most Missouri Februarys have a number of days above freezing. A notable exception to the rule that late winter is best for pruning is the case of spring flowering shrubs like forsythia and lilac. These species should be pruned just after flowering to avoid removing the flower buds before they bloom. Refer to a previous article entitled Shrub Pruning Simplified in the August issue of MEG to determine which shrubs should not be pruned (http://ppp.missouri.edu/newsletters/meg/archives/v8n8/meg6.htm ) in February and March.

Many people seem to have the idea that all woody plants need annual pruning. This is not necessarily the case. In fact, if you can’t think of a good reason to make a pruning cut, don’t do it. Luckily for those with itchy pruner fingers, there are some good reasons for pruning. The primary objective should be to promote plant health and vigor. For the first few years after planting, regular pruning can help to develop a strong branch structure, reducing the chance of storm damage. Occasional pruning of established trees and shrubs can thin out crowded branches, allowing better light penetration and air circulation to create an environment less conducive to disease development. It also promotes vigorous shoot growth, often making the plant less vulnerable to attack by insect and disease pests and improving bloom display. Pruning out broken, diseased or dead branches is also a good plant health maintenance practice. This year, pruning off the black tips on ornamental pears caused by fire blight will help reduce the incidence of the disease when it strikes again at bloom time. Be certain to cut back to several inches below the blackened bark, since the bacterium that causes fire blight survives in the sunken bark cankers caused by the disease. Do not attempt to prune high branches without the proper equipment. Two of my friends have had life-altering experiences with ladders recently.

Pruning for tidiness should come in a distant second to pruning for plant health. While there is nothing wrong with pruning back an errant branch to maintain symmetry, annual pruning to force a plant into an unnatural form usually means one of two things. Either the plant was planted in a space that was too small or the person doing the pruning feels a need to dominate nature. Fortunately, the trend seems to be toward less formal and more natural-looking landscapes, reducing the temptation to practice phyto-geometry with pruning tools. When deciding how to prune, look at the plant from all directions to identify correctable problems. These could include crossing or rubbing branches, narrow branch angles, shoots growing toward the center of the plant or just excessive branch density. Spend a few minutes mentally pruning before pressing the tools into action. Then, start by removing the broken, crossing and rubbing branches and those growing directly toward the center of the plant. When making cuts, always cut back to ¼ inch above a lateral bud or to the junction with another part of the branch. Never leave stubs with no obvious buds on them. When cutting to a bud, choose one that faces outward, away from the center of the plant. Try to maintain the natural form of the plant. If, for example, a young tree has a dominant central stem (leader) all the way to the top, removing the tips of potentially competing branches near the top will allow the main leader to remain dominant. Also, removing small branches that have developed at an angle less than 40 degrees with the main leader will help to develop a strong framework of main branches. If the density of branches seems too great, thin out some of them by cutting back to the main stem to a junction with a larger branch or to the ground. Finally, if some branches are growing out of bounds, tip them back to slow their growth and cause them to produce more lateral branches.

Always keep in mind that pruning has an invigorating effect on plants. Excessive pruning tends to promote long, lanky, vertical shoots. For this reason, it is much better to prune a little every year than a lot every five years. If a plant has been neglected for several years, it is often best to prune moderately over a two or three year period to get it back under control.

For more information on pruning techniques for trees and shrubs, see http://muextension.missouri.edu/explore/agguides/hort/g06870.htm and http://muextension.missouri.edu/explore/agguides/hort/g06866.htm

Chris Starbuck, Woody Ornamental Horticulture, UMC (573) 882-9630