Pruning shrubs in winter can pay off big come spring
Midwinter is an excellent time to prune deciduous shrubs.
“Because they’ve lost their leaves, it’s easy to see the structure and judge which branches to remove,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at the Morton Arboretum in Lisle.
For most shrubs, it’s best to prune selectively, removing only those branches that need to go. “Take out branches that are obstructing a path or window, or that are making the shrub look lopsided or ungainly,” she said.
If a shrub has grown too large, removing the longest branches — a process called heading back — can often bring it down to a more manageable size.
Mature shrubs often benefit from a technique called renewal pruning, which opens them up and spurs vigorous new growth. It can also detangle an overgrown shrub, allowing light and air to reach the interior. In flowering shrubs, it encourages more blooms over time.
To renew a shrub, choose one-third of the oldest stems or branches to remove each year. Cut branches back to where they join a main stem, or remove entire stems on a multi-stemmed shrub by cutting them an inch or two from the ground. After three years, the whole shrub will be new.
“Just be sure that in any one year, you never remove more than a third of the shrub,” Yiesla said. “It needs to keep enough leaves each year so it can collect energy to fuel its growth.”
A more drastic technique, for severely overgrown plants, is called rejuvenation pruning. It simply means cutting all the stems down to within a few inches of the ground. In most cases, the shrub will bounce back in a year or two.
“It looks extreme, but it can give new life to an old shrub,” Yiesla said. Once the shrub has regrown to a desirable size, she said, “prune it regularly to keep it from getting tangled up again.”
Before you prune flowering shrubs, be aware of when they bloom. Springflowering species such as forsythia and lilacs already have their flower buds in winter, so pruning them now will remove some potential blooms. “It doesn’t hurt the shrub, but it does reduce the spring flower show,” Yiesla said.
Most summer-flowering shrubs don’t create their flower buds until spring, so pruning them in winter won’t affect their bloom. There are exceptions, such as bigleaf hydrangea (Hydrangea macrophylla), so do some research on your shrubs before you snip. Detailed advice for pruning different kinds of shrubs is available at mortonarb.org/plantadvice.
Winter is not the right time to prune all shrubs. For evergreens, wait until spring. If you have a formal hedge that you customarily shear with clippers or an electric hedge trimmer, hold off until the plants have new green leaves, which will usually be in April or May. “They need to be actively growing to recover from the stress of shearing,” Yiesla said.