CORVALLIS, Ore. – Like overgrown hair, untrimmed hedges may go unnoticed to everyone but the owner. A spring trim will get your hedge back in shape and stimulate new growth.
The best time to trim is after the flush of spring growth – usually late April through early June – depending on your growing season and the vigor of the hedge materials, according to Ross Penhallegon, horticulturist with the Oregon State University Extension Service.
"Spring trimming after the growth spurt will help the hedge hold its desired shape longer than pruning before the active growth period," Penhallegon said.
Trimming also will help make the individual shrubs blend together. Make the bottom wider than the top so that light can reach all the leaves. On older, slower-growing bushes, modify the shape gradually over several years. Some older shrubs may need trimming only about one half inch per year.
Heaths and heathers will need shearing right after they finish blooming, as well. Cut just below the point where the blooms formed. Annual post-bloom trimming will stimulate new growth in the center of small shrubs and keep them compact. Apply a complete fertilizer to keep heathers and heaths healthy and robust.
Later in the spring, apply a nitrogen fertilizer to young hedges. For mature hedges, apply a complete fertilizer, such as a 16-16-16 combination, or a good composted manure once a year.
As June approaches, concentrations of spider mites may appear in hedge foliage. If the leaves develop a gray cast and look dusty, it's likely that spider mites are present.
To verify that you do have spider mites and not just mildew or dust on your shrub, hold a piece of paper under a branch of the infested shrub. Shake the branch. Tiny brownish-to-reddish specks will fall on the paper. Examine them with a magnifying glass or hand lens. If the spots begin to move, odds are they are mites, Penhallegon said.
Hose the hedge with water in the early morning to help control the spider mites, or apply an insecticidal soap.