Use caution when pruning in fall

Spring is pruning time. That’s the time of year when new growth stimulated by the pruning process will be the most successful. There are some that will claim, however, that you should “prune whenever your pruners are sharp.” While that may be (mostly) true, there are some cautions you need to consider before you try and do any end of the growing season pruning.

Woody plants move sugars and other materials from the leaves to storage places in the woody portions of the plant just prior to leaf fall. The goal of our pruning management should be to maximize those stored energy reserves. Most would agree that any pruning during the heat of summer just isn’t wise. Even pruning in the fall can cause problems. According to Penn State Extension Specialist Rich Marini: “Based on everything that has been published we can conclude that woody plants do not attain maximum cold hardiness when they are pruned in the fall. Trees are affected more by heavy pruning than light pruning.” There it is. Black and white. End of story, right?

Maybe not, and here’s why. Growing conditions in the fall aren’t always the same—and neither are species. If we prune a hardy tree species, even lightly, and it’s followed by a sharp drop in temperature before plants are hardened off, tissue damage can occur. If you were to prune a less-hardy plant, even heavily, and temperatures were moderate, giving adequate time for the plant to harden appropriately, you might not notice a thing. So what do you do?

We already saw spring mostly skipped this year. Who knows if we’ll have any fall, or winter will just descend upon us. With that in mind, prune cautiously. Start with dead wood. It can be removed any time of the year without a problem. After that, fall pruning is likely safe so long as you remove less than ten percent of the branch area. Keep in mind that even light pruning of spring-blooming shrubs such as lilac and forsythia will reduce flowers for next year—wait to prune them until after flowering.

If you want to add a little light pruning to your fall gardening chores—go right ahead. Just don’t exceed the ten percent tissue removal rule of thumb and try to plan pruning so that the tree or shrub has plenty of time to recover going in to cold weather. If you want to be on the safer side, just wait until spring.