Fall or Winter- after the leaves change in the fall but before the spring bloom. Pruning too early can harm your trees and shrubs.
The dormant stage that trees enter during fall and winter halts growth. The trees are inactive and the temperatures outside get quite cold. This is the perfect setting for pruning. Trimming after a tree has begun blooming will limit its growth potential.
Pruning your trees while they are dormant sustains its current health and promotes growth. Also, the dormancy period will save money and time by helping with management of disease.