Addy the Environmentalist in Training

Each year, well-meaning amateurs inflict horrible wounds on their trees in the name of routine pruning. Unfortunately, many of these mistakes cause long-term trouble for the tree; in extreme cases, removal becomes necessary. Avoid committing these six common tree trimming mistakes to ensure your trees stay healthy and vibrant for decades to come.

1. Improperly Placed Cuts

It is crucial to make all trimming cuts in the proper place to take advantage of the tree's natural defense mechanisms (a process called compartmentalization). Place all cuts about 1 inch out from branch junctions – never make cuts in the middle of a branch, as this leaves a large stub that is destined to rot.

2. Topping

Topping is the practice of cutting a tree's central leader – the trunk. Usually performed to reduce the overall height of the tree, topping is extremely stressful for the tree, and often causes premature death. Unfortunately, there are few ways to reduce the overall height of a tree, which illustrates the importance of selecting proper tree species in the first place.

3. Lion-Tailing

Removing the inner branches within a tree's canopy – a mistake arborists call "lion-tailing" – upsets the balance of the branches and tree. Often the result of overzealous pruning, the result is an unattractive tree that is more likely to fail in high winds. Additionally, such trees often produce an abundance of water sprouts, which further undermine the stability of the tree.

4. Over-Pruning

Removing too much of a tree's canopy at one time can severely stress the tree. The best rule of thumb is to remove no more than one-third of a tree's canopy in any year. This allows the tree to survive the pruning and cope with the reduction in leaves. If you must prune more than this, wait until the second year to complete the task.

5. Painting Stubs

While arborists of the past often painted branch stubs to protect them from fungi and disease, research has shown that this is not necessary. In fact, these paints prevent the wound from drying, which leads to rapid decay. Simply make clean cuts at the proper location along the branch, and allow the tree to compartmentalize the wound naturally. 

6. Poor Timing

Trimming trees during the wrong part of the year causes stress and exposes them to pathogens. While the best time for pruning a tree varies from one species to the next, you should prune spring-flowering trees in the early summer, after they bloom, but prune summer-flowering trees in the winter, before they bloom.