Purdue Extension Service

Vanderburgh County, Indiana

Does Time of Year Matter for Pruning Trees and Shrubs?

By Larry Caplan, Extension Horticulture Educator, Vanderburgh Co., IN

For the Evansville Courier and Press, February 1, 2008

There are two philosophies when it comes to pruning. One is that trees and shrubs must be pruned at certain times of year, or all sorts of catastrophic things will happen. The other school of thought is "prune whenever your saw blade is sharp." As with all things, the truth is somewhere in the middle.

It is virtually impossible to damage a large, mature tree by pruning it at "the wrong time of year." Trees are fairly slow to respond to changes in their environment. And while research has shown that the wounds respond better when pruning is done during periods of active growth, it's probably not enough of a factor to cancel a visit from your arborist if he can make it to your property in the fall.

Shrubs, however, respond much more quickly. A late summer or early fall pruning may spark a flush of growth at a time when the plant should be going dormant for the winter. This often leads to serious cold injury, especially if we get an early freeze.

The most important consideration on timing shrub pruning is flowering. Pruning at the wrong time can diminish or even eliminate this year's blooms.

Many plants bloom very early in the spring. These plants include crabapples, forsythia, certain hydrangeas (oak leaf and big leaf types), flowering plums and cherries, and honeysuckle. All of these plants form their flower buds during the previous summer and fall. The flower buds remain dormant on the plant throughout the winter, and will pop open during the first warm days of spring.

This is important to know because if you prune these types of plants in the winter or early spring, you will be cutting off and throwing away the flower buds. This won't hurt the plant, but it will reduce your flower show for this year. In fact, pruning at the wrong time of year is the number one reason most gardeners have problems with their hydrangeas blooming. If the flowers are important to you, you might want to wait until immediately after the blooms fade before pruning.

Summer flowering plants, which include roses, butterfly bush, smooth and Pee Gee hydrangeas, and coralberry, produce their blooms on the current year's new growth. The more new growth they produce (within reason), the more blooms you'll have. These plants should be pruned before growth begins in the spring, to encourage vigorous new growth.

Plants with no flowering interest, such as yews and junipers, can be pruned any time the wood is not frozen. Again, beware of doing heavy pruning in late summer.

Be sure that you know the correct way to prune your trees and shrubs. Hacking the plants back is almost always the wrong way, and will cause many problems besides lack of blooming.

For more information on pruning, contact the Purdue Extension Service at (812) 435-5287.