The best time to prune any woody plant is just before new growth starts. The worst time to prune is right after leaves emerge in spring. Pruning in late winter or early spring while a plant is dormant will not adversely affect its vigor; but pruning at other times can rob it of stored food energy. Severe pruning during or just after active growth in spring only wastes stored energy. Such pruning can dwarf a plant and is not recommended unless a dwarfing effect is the goal, such as for a bonsai.
Pruning is done to improve the appearance of the plant, remove dead, damaged or diseased wood, to improve the quality of flowers, fruit, foliage or stems, and to restrict the plant’s growth. Prune damaged plants as soon as possible to avoid additional insect and disease problems that may develop.
Our basics section has more information on pruning trees and pruning fruit trees.