When to Prune

When should you prune your trees? It is a question that I get asked a lot. I keep on thinking that there should be an easy answer for this. Most pruning that we do is not time-sensitive. However, there are some plants and types of pruning where timing is important.

How do I find out when my trees should be pruned? Many of us go to our favorite internet search engine to answer questions like, “When to prune oak trees.” The internet has some great information, but it can be misleading. If you search “when to prune oak trees” you will likely see that you should only prune them from November to April to avoid the spread of oak wilt. Oak wilt is an aggressive, lethal disease that can kill entire groves of oak trees. Timing your oak pruning is incredibly important if you live in the Midwest or Texas, where oak wilt is a problem. In the Richmond area, it is not an issue.

The species of tree matters, but why you are pruning also matters. If you aggressively cut your crepe myrtle to control its size, late winter is the time for pruning. If you are thinning, removing deadwood and making some modest cuts to raise the crown, there really isn’t a bad time to prune your crepe myrtles.

Here is a short and, admittedly, incomplete list of rules that will hopefully give some guidance on your decision of when the time is right to prune your tree or shrub.

• American Elms: Dutch elm disease is a concern. Pruning does not cause the disease, but there is some concern that the smell of fresh cut elm can attract the elm bark beetle, which carries the disease. If pruning during the growing season can be avoided, it should be. If a branch is partially broken, or rubbing on a building, the tree is going to have fresh wounds anyway, so sometimes pruning during the growing season makes sense.
• Sappy trees: Some trees like maples and birches push a lot of sap in the late winter when the days are warm and the nights are below freezing. If these trees are pruned during this season, sap will flow from the cuts. This doesn’t negatively impact the tree at all. If it bothers you, wait until summer to prune the trees.
• Slippery bark in the spring: When some trees and shrubs are just flowering or getting ready to grow in the spring, it is very easy to damage bark and watch it peel when you are making a cut. If this is happening, use a sharper tool, be a little more careful; or just wait until summer.
• Structural pruning: When pruning young trees to improve their structure, it is beneficial to see the form without leaves on the trees. This is best done in the winter in order to make better pruning decisions.
• Spring flowering trees and shrubs: The usual thought is to prune these within a few months of when they flower so that you don’t cut out next year’s flower buds. If you want to maximize flowers and you are making a lot of cuts, this makes sense. If you are making a few minor cuts, or removing deadwood and broken branches, you probably won’t notice the difference in flowers; prune away.
• Fruit trees: Usually, fruit tree pruning is done in the winter. It should be noted that if you don’t know when to prune your fruit tree, you probably do not know how to prune it either. Take a class or do some serious reading before you pick up your saw or loppers.
• Broadleaf evergreen shrubs (like hollies): If you are pruning to maintain shape and size, late winter is great for aggressive pruning. Birds aren’t nesting yet, but they don’t need cover as much as in the middle of winter. The shrubs will push out some new growth in the spring, so if you give a “bad hair cut” you won’t have to look at it very long. You can do some light touch-up pruning until the late summer and fall – it may stimulate new growth that won’t have time to harden off for the upcoming frost.

There are, of course, more rules for when to prune, but I would warn you not to get too overwhelmed by them. I have seen a lot of pruning mistakes over my years of being an arborist (and I have made a few myself.) Most of the issues that I have seen from pruning have not been from when the cuts were made. The issues are usually from how the tree was pruned.