If you're like most people, you've got a sad-looking, post-winter hedge bordering your yard. Rows of thickly planted shrubs can be a handsome way to define borders and boundary lines, keep children and pets in (or out), and give birds shelter and even food. But like all shrubs, hedges need regular watering, feeding, and pruning to look their best. Though folks may forget to give roots a good drink in hot weather or to fertilize in early spring with a good 10-10-10 formula, the last area is where most of us really lose it. "A lot of people are intimidated by pruning, but it's a science anyone can master," says This Old House landscape contractor Roger Cook. "You just have to learn a few basics."
Mistake #1: Shearing hedges without hand-pruning them
Using shears-whether hand-held pruners with long scissorlike blades or a power trimmer-to take off branch tips keeps hedges neat and tidy, and also stimulates bud production near the plants' edges. But as buds multiply, a shrub can get so thick that sunlight can't penetrate it, preventing interior growth. The result: a hedge that gets larger each year and looks lifeless inside. Proper pruning allows some sunlight to get in and enables you to cut back shrubs so they don't get too big.
So at each shearing, be sure to use bypass hand pruners to create some spaces in the hedge for light and air. Every few feet, reach inside and clip a branch or two at a 45-degree angle, just above a nub or leaflet that's growing in a direction you want to encourage.
If a hedge is old and seriously overgrown, you'll need to do some rejuvenation pruning using the three-year rule. Remove up to one-third of the thickest stems down at the base of the plant, stimulating new growth; repeat the next year, and the year after. This will leave you with a healthier shrub that's reduced in size.
Mistake #2: Pruning at the wrong time
Ideally, hedges should be pruned in late winter, when plants are dormant and haven't produced buds-particularly if you're cutting back drastically. "You don't want them to break bud before you prune because you want the plant's energy to go toward producing new growth where you want it," says Roger. "If you take off a plant's buds, you're cutting off spent energy, and it will take longer for the hedge to fill out."
Evergreens, in particular, require pruning early in the season; because they're generally slower-growing, they're likely to be bare (where interior cuts have been made), and off-color at the tips (too yellow) as new growth starts to show, well into the summer. Faster-growing deciduous hedge plants such as privet, spirea, and viburnum are more forgiving. With flowering shrubs, the golden rule of pruning is to wait until the day after blooms turn brown-that way the plant will have time to set buds for next year, whether it blooms on the current season's wood or the next's.
Mistake #3: Not shaping a hedge so the top is narrower than the bottom
Left alone, most hedges will start to widen at the top, where they receive the most sunlight. This results in a V shape that shades out lower branches so they produce less and less foliage. "You want to turn that V upside down," says Roger. A sheared hedge should always be wider at the bottom and narrower at the top, whether that top is flat, pointed, or rounded. When shearing, start at the bottom and work up toward the top. For absolute precision cutting, you can also run a string line between stakes to ensure an even line along the top, but Roger prefers to rely on his eye for a more natural look.
Remember that once you buzz-cut the top of a plant, it is more prone to snow damage (broken branches) because it won't shed snow as readily. Tall hedges benefit from being tied up for winter-just be sure to use rope or chain lock (plastic tree-guying material) rather than hose-covered wire, which can girdle the trunks if left on too long.
For even more ways to ruin your hedges, go to thisoldhouse.com