The best time to trim trees is when the tree is dormant. In most cases, trees and plants are dormant from November through March. Pruning when the leaves are gone provides better visibility and fewer pests and pathogens are less likely to enter the tree.
Flowering trees are typically pruned immediately after they flower in the spring. Flowering trees that bloom in the summer or fall are pruned in late winter or early spring during their dormancy.
The worst time to prune trees is during late summer and early fall. Pruning during this time encourages new growth, preventing the tree from entering its natural dormancy. The tree will struggle to heal in time for the cold season and could die.
Mature trees should be trimmed every 3 to 5 years, while younger trees need trimming every 2 to 3 years.