Pruning depends on your purpose

There you stand, pruners at the ready, facing a dormant shrub on a winter’s day. Where exactly are you going to cut?

“It depends on what you’re trying to accomplish,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle.

Maybe you just want to tidy up the shrub or even it out, because a few branches are sticking out awkwardly or are obstructing a path or a window. “First look the plant over carefully and identify the problem branches,” she said. “Then cut back only those branches you’ve selected.”

You can either cut a stem all the way back to an inch or two above the ground or cut it partway back to shorten it. In that case, make your cut just above a side branch or a lateral bud — one of the buds that grows along the side of a branch. When you cut a stem to the ground, it’s called a thinning cut; shortening it to a side branch or a lateral bud is called a heading cut. Step back often and decide whether you’ve done enough. “It’s a little too easy to get carried away,” she said.

As you work, remove any dead wood and any branches that are interfering with each other. “If two branches are rubbing against each other, or will be rubbing when they get a little bigger, remove one of them,” she said.

Sometimes your goal may be to reduce the overall size of the shrub without destroying its natural form. In that case, shorten all the stems, using heading cuts. “You’ll want to prune the shrub back a little smaller than your ideal size, to allow for new growth in spring,” Yiesla said.

Over time, many shrubs will become too crowded with new and old stems. For them, the recipe is what’s called renewal pruning — removing older stems to favor newer ones.

Aim to take out no more than a third of the shrub at a time. Identify the oldest stems — they will be thickest, usually with thicker, more textured bark — and cut them down to the ground. Do the same every winter for three years, and you’ll have an entirely rejuvenated shrub with only new growth.

In some cases, a long-neglected shrub can become a dense, impenetrable, overwhelming tangle. “That may call for more drastic measures,” Yiesla said. “You can often rejuvenate an old shrub by cutting all of its stems right down to the ground.”

The bunch of short stubs that is left may look pitiful at first, but new stems will soon sprout. In two or three years, the shrub will likely be back to full size. “To keep it from becoming a tangle again, take out a few of the oldest stems each year,” she said. “Just be sure you never prune out more than a third of the shrub at a time.”

Not all species of shrubs will respond to this rejuvenation pruning. It works best for forsythia, weigela, privet, honeysuckle, spirea, and hydrangea. For more pruning advice, see mortonarb.org/pruning-deciduous-shrubs.

“The key to pruning is always to know why you’re doing it,” Yiesla said. “Some shrubs may not need it every year. Others need regular attention to keep them from getting too large or too overgrown, and winter is a good time to give it to them.”

For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or [email protected]). Beth Botts is a staff writer at the Arboretum.

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