Trimming trees and shrubs can be accomplished throughout the year; however, it is ideal for the home gardener to follow certain guidelines regarding when to prune. Different plants within the landscape demand pruning during different times or seasons. In general, you should prune plants when their growth is dormant during the early spring or late winter. Fall, though not ideal, is also a popular time to prune—particularly in areas where late winter weather is not conducive to gardening. Removing branches during the active growing seasons of spring and summer is generally not recommended.
The most important rule for determining when to prune is to choose a time of year that will cause the least possible damage to the plant. Pruning during the heaviest period of new growth, which takes place in spring for most plants, is rarely recommended. Plants store a great deal of nutrients and energy in their roots and branches, and removing limbs during this critical period can result in stress and stunted growth. Likewise, pruning during the summer has the potential to encourage new growth in the plant that will not have sufficient time to mature and harden before the fall and winter set in.
Trees and shrubs have unique growing patterns and characteristics that require pruning at different times. As you decide when to prune in order to maintain optimum health of a plant, take the individual qualities of the specimen into consideration. In general, fruit, ornamental, and shade trees prefer to be pruned in the wintertime. Shrubs that flower in the spring can be pruned right after the blooming period, while plants that bloom in the summertime should be trimmed either the coming winter or the following spring.
Certain flowering plants and shrubs set their buds in the fall. Care must be taken as you are choosing what and when to prune that you do not remove these budded branches in the early springtime. Doing so will result in a loss of flowers, as there will be no blooms on the new year's growth.
One common exception to the spring and winter pruning guidelines is a plant that is suffering diseased, broken, or dead limbs. These weak and injured components can damage the tree or shrub, and commonly recommended guidelines concerning when to prune do not apply. In these cases, you must take care and be conservative, removing only what is absolutely necessary.