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A frequent question that I receive regards the time of pruning trees. Just when is the best time? There are several ways to approach this question.

First, if the tree has plenty of space to grow, it may not need pruning at all, unless there is some structural or safety defect that needs to be addressed. If a tree has been damaged, or is growing in such a way to cause concern for safety, or if it is growing branches in a location that is "just in the way," then pruning is a good idea.

Especially in the case of an unsafe tree, prune immediately, no matter what time of the year it is. Most of this article will address the "ideal" time to prune, but that is just for trees which do not need immediate attention. If a limb is about to fall on your house, forget about the "ideal" time to prune.... the ideal time is immediately.

Assuming that there is no damage to the tree that needs correction, or a safety concern, I will next ask what kind of tree it is. Evergreen trees are treated differently than deciduous trees. You can usually prune evergreen trees at any time of year, but generally I prefer the time frame of late winter to early spring.

When it comes to deciduous trees, the ideal time to prune them is in late winter to early spring, before the trees leaf out. The reason is that late summer and fall pruning often promotes new succulent growth, and this is more subject to winter injury. If you wait until the tree is dormant, you won't have this problem.

Sometimes I do hear from people that have pruned certain species of trees in the early spring, and the trees are "bleeding" profusely. This is especially true of birches and maples. While it may appear that the tree is "bleeding to death," it really is not harmful to the tree. During the early spring, deciduous trees are starting to break dormancy. Even though they may have not leafed out yet, they are fully capable of forming new callus tissue over pruning wounds. In fact, this is the best time of the year for wound healing. So any "bleeding" will only be temporary, and should not be of major concern. If you are pruning a species which is subject to "bleeding," and are concerned about it, just wait till later in the spring, when the tree has leafed out, and you shouldn't see as much of this activity.

Another reason not to prune in later summer or fall, before the tree goes dormant, is that there is a reservoir of nutrients in the leaves at that time. By pruning them, you will be removing those nutrients.

In the fall, as the tree prepares for winter, it removes those nutrients from the leaves and branches and puts them in the trunk and roots, before going dormant. Abscission layers then form, and off come the leaves. If you interrupt that process by pruning the leaves and branches off, you have removed a large source of nutrients, which is a stress on the tree.

Another advantage of dormant-season pruning is that there are no leaves in the way. You can more easily see what you are doing, and how you are shaping the tree.

And one final precaution. Remember that if you are pruning a spring-flowering tree, that you are removing flower buds, and the tree will be less showy when it blooms. This also applies to spring-flowering shrubs, such as forsythia.

Having said all that, if a tree really needs to be pruned in midsummer or even the fall, then by all means prune it. Again, this is especially important if safety is an issue. But be aware that the tree will be slower to heal over during this time, compared to later winter or early spring.

If you would like more information on pruning, including techniques for pruning deciduous trees, please call your local Extension Center and ask for Guide Sheet G6866, "Pruning and Care of Shade Trees." We'll be happy to send you a copy.


		Sarah Denkler, Horticulture Educator University of Missouri Extension P.O. Box 160, Kennett, MO 63857 573-888-4722 Denklers@missouri.edu Updated 04/18/08

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