okPLANTtrees - Resources - Educational

Pruning your Shrub

Shrubs can be pruned to improve their shape or to control their size. Generally, this can be done at any time. Shrubs that bloom in the spring, however, should be pruned in the late spring or early summer after they have finished blooming. These shrubs bloom on last year's wood. Trimming them in the late summer or fall will remove the buds and diminish the next spring's bloom.

Deciduous Shrubs
Early spring blooming shrubs will be opening flowers that were formed late the previous summer. Severe pruning during the winter will cut off these potential flowers. Delay pruning Forsythia, Spring Spireas, Snowball Bushes, and other Viburnums, Lilacs, and Flowering Quince until after they have bloomed. Prune to control the size of the plant and most importantly to get rid of old wood so that the plant continues to flower well. Each year or two cut out some of the oldest wood to the ground, leaving the younger branches (but never more than a third of the bush).

Making a pruning cut just past a leaf node results in more side branches forming. This produces a bushier shrub and can control the height of the plant. Continued shearing over time can leave the plant looking dense and very formal. With this method, keep in mind that leaves form where they can receive light. Shape the plant slightly slanted so that light reaches the lower branches too.

To have a more informal shaper to your plants, trim by individual cuts rather than quick, overall shearing. It takes more time but keeps a natural look longer. Shorten some branches while letting others grow normally to be trimmed next year.

Evergreen Shrubs
Shrubs that keep their leaves during the winter can require a different pruning method than those that shed to bare branches. Very extensive pruning will leave your shrub with a "bad haircut" to look at all winter. Anything but a light trim might be better left to do in late February so that new growth will soon follow to fill the bare spots quickly.

References:
Tree Pruning: A Worldwide Photo Guide. Shigo, Alex L. c. 1989. Shigo and Trees Assoc. Durham.