Winter prime time for pruning

Winter is a fine time to prune most trees and shrubs. Without leaves, the structure of their stems and branches is easy to see.

“You can spot problems that would be hidden by leaves in the summer,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle.

While the plants are in their winter dormant state, they won’t respond to pruning with new growth, as they would during the growing season. Plants generally are dormant from the time the leaves fall until early March, depending on the weather.

Pruning in winter also offers protection from some plant diseases that can spread through open wounds. “It’s a real danger for oaks in particular,” Yiesla said. “Oaks should only be pruned while they are dormant.”

Here are some tips from the Plant Clinic for dormant pruning.

Sharpen your tools. Clean, sharp blades on your pruners or loppers will make cleaner, healthier cuts. Dull blades crush or tear at the wood, making mangled wounds that are harder for plants to seal over and that are more likely to admit insects and disease. Replace a dull blade on a pruning saw.

Prepare to disinfect. To avoid carrying disease pathogens from plant to plant, disinfect your tools often as you work. “A small spray bottle full of rubbing alcohol makes it easy,” Yiesla said. At a minimum, disinfect your tools each time you move on to a new plant.

Have a plan. “Before you make your first cut on a shrub, figure out what you’re trying to accomplish,” she said. Do you need to thin the shrub because it’s overgrown and tangled? Are there branches that intrude on the walk or block a window? Are there broken branches? Is the shrub lopsided? “Not every shrub needs pruning each year,” she said. “Prune for a reason.”

Prune for natural form. Most shrubs will look better if you prune them branch by branch with hand pruners, keeping the soft, natural form. “Use an electric hedge trimmer only on evergreens that are intended as formal, geometric hedges,” Yiesla said.

Take out dead wood first. All shrubs and trees accumulate some dead stems and branches over time. Start by removing those, and then any branches that show signs of disease. Then step back and consider which live branches you may want to remove.

Remove older, thicker stems. In general, younger wood grows more vigorously and flowers more than older wood, so lean toward removing older stems.

Make cuts at the ground or near a main stem. Either cut off an entire stem an inch or two off the ground, or cut a side branch close to the main stem. The goal in pruning branches is to preserve a special kind of tissue that grows around the base of each branch and allows the plant to seal over the wound. “Don’t leave stubs an inch or a few inches long, because the plant can’t repair those,” she said.

Know when your flowering shrubs bloom. Spring-flowering trees and shrubs have already formed next year’s flower buds before winter, so when you prune them, you will be removing potential blooms. On the other hand, most summer-flowering shrubs don’t form buds until spring, so removing stems in winter does not affect their flowering. “If you do remove flower buds, it won’t hurt the plant,” Yiesla said. “It will just reduce the number of flowers you see in spring. Shrubs can’t bloom on stems they don’t have.”

Get more advice. For detailed advice on pruning techniques and on when to prune ornamental shrubs by species, see mortonarb.org/pruning-deciduous-shrubs.

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