By: Tom Smiley, PhD

We know many of the common causes of tree failures, and some of them can be prevented when the trees are young. One of the keys to developing strong trees is the process of structural pruning, or pruning to improve tree structure. 

With young trees, our goal is to prune them to create a structure that is resistant to future breakage, won’t interfere with people, looks good, and is long lived. The earlier we start on this process, and the more regularly it is repeated, the better the results will be.

When structurally pruning a young tree, we carefully look it over and make decisions as to which branches to remove. We identify the central leader of the tree. This is the tallest, most centrally located, healthy branch. Other branches that are growing upright near it are reduced or removed. This eliminates one of the most common failure points on mature trees, the codominant stem union.

We also identify the lowest permanent branch on the tree. Many lower branches, if allowed to grow, will interfere with pedestrians, vehicles or buildings. Branches below the lowest permanent branch can be reduced or removed while the tree is developing so that large cuts won’t be needed later. Smaller cuts reduce the risk of decay moving into the trunk. Ideally, we like to see all the lower branches be half the diameter of the trunk.

While we are making these cuts, we also try to maintain as many lower and interior branches as possible. We like to have foliage on the upper two-thirds or more of the trunk. In general, lower branches are good and contribute to the development of a strong lower trunk and root system. 

A lot goes into structural pruning. The exact cuts will depend on the tree species and location in your landscape. If we start the process shortly after the tree is planted and continue on as it matures, the result is a strong, long-lasting and healthy tree.