Winter is a fine time to prune deciduous shrubs. When the leaves are gone, you can see the true form of the plant to help you choose which branch to cut. How you prune will depend on each shrub’s situation, says Julie Janoski, Plant Clinic Manager at The Morton Arboretum
Heading back pruning: If your goal is to control the size of a shrub, balance its shape, remove dead or damaged wood, or open it up a bit, take it branch by branch. Using clean, sharp bypass pruners, cut just above the place where one stem branches off from another. Pause often and step back to consider the effect of your pruning so far and whether you’ve done enough.
Renewal pruning: If a shrub is thickly overgrown, you can clear it out and renew its vigor in stages. Each year, cut out some of the oldest, thickest branches down to the ground, removing about a third of the plant. In spring, new stems will sprout and in three years the whole plant will be renewed. Cut the older branches as close to the ground as you can using clean, sharp bypass pruners or a pruning saw. Distribute your cuts around the plant, rather than concentrating on one area.
"At the end of three years, you'll have removed the entire plant, and it will all have been replaced with new growth," Janoski says. You remove only one-third of the plant each year, so "you're not going to create a gaping hole in the landscape."
Rejuvenation pruning: If a bush has become dauntingly huge and dense, drastic action may be called for. Most deciduous shrubs can be entirely cut back to within an inch or two of the ground in late winter.
For renewal and rejuvenation pruning, the shrub must grow multiple stems from the root ball. This is true of species such as Weigela, spirea, common lilacs, and arrowwood viburnum. If you have a shrub with only one stem, use the heading back pruning technique.
New growth will start in spring and in a couple of years the shrub will be back at a good size. Then you can keep it under control with regular selective pruning. For spring blooming shrubs, pruning in winter will eliminate the flower buds, so wait to prune shrubs such as viburnums and lilacs after the blooms have come and gone.