Prune to keep ornamental shrubs healthy

gardening image
Ross Penhallegon gives pruning advice. (Photo by Lynn Welp.)
Last Updated: 
March 19, 2012

CORVALLIS, Ore. – As winter moves toward spring, pruning jumps to the top of the gardening "to-do" list. Pruning keeps ornamental shrubs healthy by removing dead, dying and diseased wood and encourages the natural and sturdy growth of the plant.

"Pruning is one of the most important tasks to keep shrubs and bushes healthy," explained Ross Penhallegon, horticulturalist and pruning expert with the Oregon State University Extension Service. "Yet pruning often gets neglected or forgotten."

Basic pruning guidelines deal with the many sizes, shapes and growth forms of ornamental shrubs. Most gardeners should do some pruning each spring and/or summer if they have spring or summer bloomers, Penhallegon said. Shrubs that bloom in the early spring, such as forsythia, rhododendrons and azaleas, should be pruned when they finish blooming. Then they have the rest of the growing season to form new branches and flower buds.

Shrubs that flower in the summer and fall are blooming on this year's growth. They should be pruned early in the dormant period or very early spring so there's plenty of time for new growth to form and bloom.

"Sometimes it's worth it to prune out of season and sacrifice a year of blooms," Penhallegon said. This is the case when the bush is overgrown, has gangly branches or has been neglected for years. This type of pruning should be done in the dormant or winter time.

Light pruning can be done in the summer, when it's easy to spot dead, dying, diseased, or weak branches with few leaves. Pruning in the winter allows you to see how the branches grow in relation to one another. Branches growing toward the center of the plant or crossing or rubbing other branches are good candidates for removal. This kind of maintenance pruning in itself reduces the size of the plant if it is too large.

If you prune regularly every year, you never need to prune too severely. Yearly pruning keeps the plant in good condition with new and old branches and some in between. If the plant grows too tall or large from lack of pruning, it can overwhelm neighboring plants and surroundings.

"A little pruning each year helps to keep the plant in bounds, keeps it healthy, allows good light penetration and encourages blooms every year," Penhallegon said.

Shrubs can be pruned drastically if they get out of hand and need rejuvenation. Multi-stemmed species such as spirea and forsythia can be heavily pruned by removing the older stems or branches, lowering the height of the plant. Rhodies and azaleas can be heavily pruned to 12-14 inches or just above buds that are on the lower part of the plant.

An overgrown shrub with a single lead or trunk growth form needing rejuvenation should be gradually pruned down or brought under control to maintain the natural form of the plant. Don't be tempted to shear off the top of this kind of plant. Always cut back to a good side branch. Shearing may be faster, but it will produce a leggy plant with brushy growth at the stem ends. Each cut will often produce two more branches. Some large shrubs, like laurel, will sprout from bare wood even when they're cut back nearly to the ground. Evergreen shrubs, both broad-leafed and needled, should not be pruned back to bare wood.

With so many existing ornamental shrubs and so many new ones showing up in the market place yearly, Penhallegon recommends keeping a pruning book at hand. "Follow good pruning practices and your plant will look good all year."

Author: Judy Scott