How do I trim overgrown hedges and shrubs?

Bring an overgrown shrub back in stages rather than in one hard cut. Clear out the dead and crossing wood first, then remove about a third of the oldest stems at the base each year, and keep hedges wider at the bottom than at the top. A plant that has been neglected is difficult to prune, and one that has outgrown its space may be better replaced^[4] with a variety that stays the size you need.

Start with timing

Cutting at the wrong time costs you a year of flowers or invites winter damage. Virginia Tech's rule of thumb is to prune shrubs that flower on old wood just after they bloom,^[1] because their buds for next spring form the summer before. Shrubs that flower on new wood, such as butterfly bush and crape myrtle, can be pruned any time after they flower until just before they leaf out in spring.^[1] Shrubs without showy flowers, such as yews, barberries and boxwood, can be pruned most any time except late summer,^[1] because late-summer pruning tends to push a flush of new shoots that may not harden off before winter.^[1] Our guide to when to prune shrubs in Virginia has the season-by-season version.

Tools that fit the cut

Hand pruners handle branches up to 3/4 inch thick, loppers 3/4 to 1-1/2 inches, and a pruning saw anything larger.^[4] Keep blades sharp so they cut cleanly rather than crush. Remember that hedge shears are meant for hedges and formally shaped plants, not general pruning;^[4][5] shearing an informal shrub all over makes it denser on the outside and bare inside.

Renewal pruning: the safe way back

Most overgrown deciduous shrubs, and many broadleaf evergreens, recover best with renewal pruning. Each year, cut up to one-third of the oldest, thickest stems^[5] down to the ground. New shoots grow from the base, and in about three years the shrub has been rebuilt from young wood without ever looking butchered. Once the thick, overgrown trunks are gone, you switch back to ordinary maintenance pruning.^[5]

Before the renewal cuts, walk around the plant and take out the obvious problems: dead or broken branches, branches that cross or rub, suckers from the base and shoots growing back into the center. Often that alone opens the plant up more than you expect.

For a faster reset, some multi-stemmed shrubs tolerate rejuvenation: cutting all the canes back as close to the ground as possible in early spring.^[5] It works on overgrown spirea, forsythia, cane-growth viburnums and honeysuckle^[5] that are otherwise healthy. It is not a method for evergreens in general.

Evergreens need a lighter hand

Evergreens differ a great deal in what they forgive. Yews can often survive a 50 percent size reduction,^[4] but junipers seldom grow back from bare stubs, so green foliage has to stay on every branch you cut back.^[4] Arborvitae and junipers develop a dead zone in the center^[4] where there are no leaves, and cuts into it leave holes that will not fill. As a limit, overgrown arborvitae should not be cut back more than 20 percent.^[4] If an arborvitae screen is far too big, replacing it is often the honest answer.

Azaleas and rhododendrons need patience too: never cut into areas of bare stems or sparse foliage,^[4] and when a heavier pruning is needed, no more than one-third of the branches should be cut back in a single season.^[4]

Boxwood is better thinned than sheared. Dense boxwood, such as English boxwood, benefits from removing 3- to 6-inch pieces of branch tips throughout the canopy,^[2] which lets light and air into the middle and makes disease less likely.

Shaping a hedge

Whatever the plant, always trim so the base is wider than the top.^[4][5] A hedge with a wide top shades its own lower branches, and the bottom goes thin and leggy. Once a hedge is at the height you want, prune new growth back whenever it grows another 6 to 8 inches, to within 2 inches of the last cut.^[5] That keeps it creeping outward slowly instead of jumping a foot a year. Stretching a string between two stakes gives you a straight top line to follow.

Keep boxwood blight out

Boxwood blight spores can travel on pruning tools, clothing and equipment,^[3] so Virginia Tech's advice is to sanitize tools between boxwood plantings and avoid working in boxwood when the foliage is wet.^[3] If your boxwood are already browning, read why boxwoods turn brown before you prune them.

Stop and call a pro if

• There is an overhead wire anywhere near the shrub. Virginia's Overhead High Voltage Line Safety Act bars anyone working in a trade or business from causing a person, tool or ladder to come within 10 feet of an overhead high voltage line,^[6][7] which the law defines as a line over 600 volts.^[7] That rule is written for crews, but the hazard to a homeowner with a trimmer is the same. Call the power company or a pro.
• You would have to hold a powered trimmer over your head on a ladder to reach the top. A tall hedge is a job for someone with the right staging.
• The stems are trunks. If the work needs a chainsaw, or the "shrub" has become a tree, it is tree work, not hedge trimming.
• The boxwood shows leaf spots, black stem streaks or sudden leaf drop. Get it diagnosed before anyone prunes and spreads it.

If the job is bigger than a weekend, see whether it is worth hiring someone to trim your shrubs and what hedge trimming costs in Virginia. Browse more lawn and landscaping answers, see hedge and shrub trimming services, or look up lawn and landscaping businesses around Blacksburg. To get quotes, describe the job once and local businesses quote it.