The dormant season of the tree in late winter or early spring, before the tree has begun to produce buds, is a good time to trim a tree. This limits the amount of time the tree has open wounds, according to the University of Minnesota.
Trimming a tree when it is planted helps begin shaping the tree from an early age. Pruning away any dead or broken branches, as well as any branch stubs, branches that rub against one another or branches that are too close together will help to keep the tree healthy.
If a tree is damaged due to insects or pests, weather problems or disease, trimming the tree can help restore it to health and prevent further problems from occurring. Pruning any damaged or dead branches from the tree limits the likelihood of fungi and pests infesting the tree.