It’s the perfect time to prune — here’s how
What’s a good winter project for gardeners? Pruning! In winter, you can clearly see structural problems in trees and shrubs when the leaves are gone, and you can prune more aggressively without stressing the plants.
Through February and into March, rejuvenate your overgrown deciduous woody shrubs with heavy pruning. First, remove the dead wood. Prune old canes off at ground level, leaving a few young canes to form the future structure of the shrub. Cut back young growth, especially if it is spindly and flops over when the large stems are removed. Cutting it back also encourages more dense growth and brings the shrub into proper scale.
If there are no young canes or not enough of them to form a new shrub, cut the large canes back to 2 to 3 feet from the ground. This may not look great, but if the plants are healthy, lots of new growth should start from the old canes in spring and fill in the plant.
Shrubs like lilacs, viburnums and forsythia that formed flower buds late last summer will not bloom the following summer because aggressive pruning removes the flower buds. Viburnums and lilacs tend to form flower buds at the ends of the branches, so even light pruning of these shrubs can remove flowers, while light thinning of stems shouldn’t affect flowering as much.
Do some research on your shrubs so you understand the impacts your winter pruning will have on their flowering in the coming spring and summer. Panicle hydrangeas flower on new growth, so they respond well with great flowering when cut back in the winter. In my experience, very old panicle hydrangeas with thick stems do not respond well to aggressive pruning.
Keep checking your gardens for animal damage, which can still happen even without snow. Snow makes it easier to see tracks, and that can be a reminder to go out and check your plants.
Rabbits can reach higher into shrubs to feed as snow levels build up. Yews and arborvitae are a couple of favorites for deer to browse. If necessary, you can install garden netting to protect your plants.
If tree branches become covered with heavy snow and ice, let the snow melt naturally rather than cracking it with a heavy object and damaging the limbs. If large evergreen branches are anchored to the ground with snow, gently sweep off snow with a soft broom and then lift the tree branch from underneath.
Remove the snow as soon as possible after it falls before the snow gets frozen to the branches. Don’t use heavy objects like shovels because you risk damaging tree bark.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.