UNIVERSITY PARK, Pa. -- Planting evergreens around a house's foundation is a landscaping no-brainer, because they stay green and require little maintenance. But a Penn State horticulture expert says foundation evergreens should be pruned to keep them looking good and scaled to the size of the house.

"So many homeowners plant large yews, junipers or arborvitae, and after a few years the plants are blocking window views," says Emelie Swackhamer, Penn State Cooperative Extension agent in Lehigh County. "The best time to prune evergreens is from December to March in the winter dormant season."

Swackhamer recommends not pruning heavily in the spring, because cuts made during the growing season will result in very dense growth on top. "The dense upper growth can shade the lower foliage so much it will die," she says.

Swackhamer says many evergreen plants can grow quite large. Homeowners that do not want to prune their plants every year should consider removing the evergreens entirely and planting shrubs that grow to a manageable size. She also says an evergreen should be pruned while it still has manageable size and shape. "Removing large amounts of growth on an oversize plant will weaken the plant and give it a 'chopped-back' appearance."

Pruning Methods

Swackhamer recommends using "heading back" pruning for evergreens. Each longer stem should be cut back to a point well inside the plant. Each cut should be made back to an emerging branch, to prevent stubs. "Branch stubs can be infected by fungi that cause plant diseases," she says.

"Proper pruning allows more air and light to penetrate the plant," Swackhamer says. "The cuts made to an emerging branch will allow side branches to develop lower in the plant, which gives the plant denser growth but does not increase size."

Heading back pruning encourages green growth throughout the plant, while keeping the natural shape of the evergreen.

Shearing

Shearing pruning, or cutting all growth back to a uniform level, should be used only if a homeowner wants the plant grown into an unnatural shape. "Turning a plant into a box or round shape removes the most attractive green growth," Swackhamer says. "The next year, you will get very dense new growth on the outside, with very little green left inside." Swackhamer says homeowners can reverse the effects of shearing by thinning out interior branches while retaining the formal shape of the plant.

Swackhamer suggests using pruners with blades that slice past each other to ensure a clean cut rather than pruners with a single blade that cut by pressing a sharp blade onto a flat surface. The latter type crushes the branches. "A crushing cut takes longer to heal," she says. " For larger branches, she recommends using lopping shears or a sharp saw.

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EDITORS: To contact Emelie Swackhamer, please call (610) 391-9840.