The best time to prune trees is usually late in the winter after the most extreme weather, according to the Arbor Day Foundation. Other times of the year may be better depending on the reasons for trimming.
Pruning a tree in late winter gets the tree ready for tremendous growth in the spring, according to the foundation. If robust growth is not desired, then pruning another time may be best. Summer pruning works to correct defects that have become visible and to limit current growth, such as that of unwanted or too-long branches. Trees with flowers blooming in spring should be pruned when the flowers wither, and trees with flowers blooming between middle and late summer should be pruned in winter or early spring. Trees should not be pruned in the fall.