CORVALLIS, Ore. – As winter moves ever so slightly toward spring, pruning works its way 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 things to do to keep your shrubs and bushes healthy," explained Ross Penhallegon, horticulturalist and pruning expert with the Oregon State University Extension Service. "Pruning is one of those tasks that often get neglected or forgotten. It's good to remember some basic pruning guidelines to cope with the many different sizes, shapes and growth forms of ornamental shrubs."
Most gardeners should do some pruning each spring and/or summer, depending on whether you have spring and/or summer bloomers, said Penhallegon. Shrubs that bloom in the early spring, like forsythia, rhododendrons and azaleas (called spring bloomers), should be pruned when they are through 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, said Penhallegon. This is the case when the bush is overgrown, has gangly branches, or has been neglected for years. You might find this situation if you move to a new place and find that the previous owners haven't pruned for several years. This type of pruning should be done in the dormant or winter time.
Light pruning can be done in the summer, which means you'll be more easily able to spot dead, dying, diseased, or weak branches with few leaves.
Pruning in the winter when the shrub is bare 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.
You'll have better results if you prune regularly every year so that you never need to prune too severely. Yearly pruning keeps the plant in good condition with some new and some old branches and some in between. If the plant tends to be too tall or large from lack of pruning, it will soon begin to overwhelm the neighboring plants and surroundings.
"Here again, a little pruning each year helps to keep the plant in bounds, keeps it healthy, allows good light penetration and encourages bloom every year," Penhallegon pointed out.
Shrubs can be pruned drastically if they have gotten out of hand and need rejuvenation. Multi-stemmed species such as spirea and forsythia can be drastically 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 this kind of plant. It 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 good pruning book at hand. "Follow good pruning practices and your plant will look good all year."