Cutting Back Big Boxwoods (& Other Overgrown Evergreens)
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Question. When I bought my house 35 years ago, one of the things that most attracted me were the three large boxwoods trimmed into balls out in front. At the time, they were about four and a half feet high. Over the years I have enjoyed these substantial ornamentals, but now have two problems. First, some of the canes on one have died, turning it into a Wiffle ball. (http://www.wiffle.com) The holes are taking a long time to fill in, and I am afraid I will disappear before some of them do. Second, over time (and despite pretty frequent and aggressive trimming) the bushes are now over six feet high, have reached window level and are beginning to look wildly disproportionate for my little house. I would like to cut them back to about four feet and maintain their ball shape. But cutting them back that drastically will remove all the leaves. Will the hedges grow back if I do so? I also have no idea when it would be best to take the plunge. The bushes keep their dark green foliage when they're dormant in the winter, and then start sending out light green leaves in the Spring. Based on this behavior, I'm guessing I ought to prune them in November. Any helpful hints would be appreciated.
- ----Greg in North Plainfield, NJ
Answer. We sent Greg our first 'helpful piece of advice' immediately upon receiving his excellent question: Don't touch them—or pretty much any other plant—now or in the near future; late summer through fall is the worst possible time to prune.
The time for pruning—especially the kind of renovation/rejuvenation pruning we're discussing here—is generally either when the plants are fast asleep during their most dormant period in winter, or right before or right after they wake up in the Spring.
(The big exception, of course, is Spring blooming trees and shrubs—forsythia, lilacs, azaleas, rhododendrons and the like. Their flower buds are already fully formed for next year, so delay any pruning of such plants until after their flowers have faded away next Spring.)
"Yes, late summer through Fall is the absolute worst time of year to prune practically anything," agrees Lee Reich, Ph.D., author of the notoriously useful tome, "The Pruning Book", which was reissued in a brand new edition earlier this year by The Taunton Press.
"Pruning stimulates plants," he explains, "and pruning a plant that's beginning to enter dormancy can often stimulate lush new growth. Even if it doesn't cause actual new growth, it stimulates cells; and either response can make the plant more susceptible to winter injury when the temperatures plunge and the winds pick up—and this is especially true of boxwoods."
Otherwise, you're pretty lucky, says Lee. "Boxwoods can be cut back pretty dramatically and they'll re-grow nicely. That's not true of all evergreens. In general, firs, Pines, spruce and other evergreens with 'whorled branches' will NOT sprout new growth in areas cut back to leafless wood. But most evergreens with random branching—like boxwood, arborvitae, junipers and yews—will develop new growth in areas cut completely back. Especially yews," adds Lee, "you can do pretty much anything with them."
"But because boxwoods are very prone to winter damage, you want to time their pruning—especially a hard pruning—carefully. The best time is that period where the end of winter meets the beginning of Spring, just before the new growth appears. Right around the time the crocuses are coming up in your area would be ideal.
"As noted, they're fast growers" says Lee, "so to re-create four-foot high plants, cut them back to around three feet and then shear them a couple of times as they're growing throughout the season; this will promote a nice dense growth pattern. The more of a distinct shape you want, the more often you should 'maintenance prune'—but lightly, like a haircut."
Makes sense—those amazing topiaries of animals and such require someone to go over them with hand pruners gently and frequently to keep the design viable. But it's often worth the effort. A 20-foot long green 'whale' carved out of a line of yews pictured in the new edition of Lee's book displays the art form brilliantly—and to great effect, as the leviathan is cleverly hiding the cinder block foundation of the home from view.
"Unless you're striving for a formal, geometric look, don't use electric hedge shears to do your pruning," adds Lee; "hand-held shears (those giant scissor-like things) will give you a much more natural look. And you can occasionally switch to hand pruners for your frequent trimming. They make it difficult to take off too much at any one time."
And what about those Wiffle ball holes?
"Sounds like it could be lack of sun," says Lee. "Even the most aggressive growers are going to develop bare spots in areas the sun can't reach. So there may be some trees nearby that have grown too large and need some pruning of their own this winter to help the boxwoods be their fullest. Check for signs of pest or disease problems as well.
"And, of course, the healthiest plants are the ones that are going to take a hard pruning best and regrow the fullest. You can't neglect proper plant care if you want nice healthy specimens to show off."