Time to prune shrubs

June 27, 1992|By Chicago Tribune

CHICAGO -- It became known as the shrub that ate the sidewalk, the evergreen yew that had grown so prolifically that tips of its foliage brushed against pedestrians walking single file.

Trimming it back to where it was no longer a nuisance would leave an ugly view into the inner branches of the bush. To try to shear it into shape gradually would take years of careful pruning. To remove the bush would be a huge chore and would leave a gaping hole in this corner lot's landscape.

"You can trim back a yew 50 percent and expect pretty good regrowth if there are enough dormant buds on the inner branches," says Greg Stack, University of Illinois Cooperative Extension adviser for Cook County, Ill. "Most people are more timid than they should be and don't cut back far enough. If you do that, however, you should supply the plant with the moisture and nutrients it needs to recover. You shouldn't leave it to fend for itself."

There is plenty of new growth on landscape plants such as evergreens, and now is a good time to restrain some of this exuberance so the plant has time to adjust to its new shape before the dog days of summer. The early-season exuberance also shows up among perennial flowers and rose bushes, where the first flush of bloom leaves many of us uncertain whether to cut back the spent flowers and, if so, where.

"It is not only necessary to cut back shrubs such as boxwood and hawthorn, but it is necessary to get it done when the flush of growth begins appearing," says Charlotte Peters, president of Charlotte Peters Gardens in Evanston, Ill. "The more energy that goes into growing those new long branches, the worse the plant looks when you cut it back.

"We had to cut down the boxwood at the Shakespeare Garden [in Evanston] last year and did it in very early spring. It looked awful at first, but as summer progressed, it filled out and this year it looks very good."

Ms. Peters says the error most people make is shearing hedge shrubs to the same point every year, causing many new tiny branches to form from the same tip. Such shearing using hand or electric hedge clippers leaves very little branching inside the shrub, she says, and causes a condition similar to witches brooming at the end of the branch.

"The best way to prune is with hand clippers and to cut back to a 'Y' or a parent branch so you get a clean look," Ms. Peters says. "There's a lot more to it, but this is important to keep in mind."

Spring flowering shrubs should be shaped up as well this month so next year's flower buds can form this summer. Mr. Stack cautioned not to trim shrubs that have yet to bloom, as that will cut off this year's flowers.

Many deciduous shrubs benefit from renewal pruning where the oldest, woodiest stalks are cut out at ground level to encourage new shoot growth. Doing it while the plant is dormant is often recommended, but Ms. Peters says it can be done almost any time after the shrub flowers.

Many perennials are hitting their stride now and, with a little pruning, can be coaxed into extending their bloom season.

"You should cut away the whole flower stalk as soon as the blossoms have faded before they make seeds, because if you wait too long, that mechanism that controls the plant's growth sends a message that it can stop making flowers now," Ms. Peters says. "Most perennials are going to flower a certain number of weeks no matter how much you cut back," she says, but there will be more flowers if the dead blooms are removed.

Other perennials will put out a second flush of bloom if the first flowers are not allowed to set seed, Mr. Stack says. "If you cut perennials back and supply the plant with moisture, you may get a second flush of bloom," he says. "It may not be as dramatic as the first set, but you'll get something."

Roses are almost in a class by themselves. Now that we've had the first flush of blooms, most types will give a continuous showing the rest of the season, depending on their care. Pruning a rose is the same as pruning a perennial -- before the plant forms seeds, or "hips," as they are known in roses.

Corrective pruning was the choice for the shrub that ate the sidewalk. The yew was hand-pruned back into the woody "dead zone" with a tapered side to allow sunlight to reach the lower branches. Two years later, that unsightly side has filled in and the new growth stretches its way onto the sidewalk again.

With the success from the first operation, perhaps this season's surgery will return the sidewalk to its full width.

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