Sometimes a shrub needs a chance to make a fresh start.
“An older bush can get so tangled and overgrown that you might think it’s beyond pruning,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “What it often needs is a particular pruning technique called rejuvenation.”
To rejuvenate a shrub, cut all the stems back to within 2 to 4 inches of the soil. This is best done in winter or early spring, before growth starts.
Usually, the shrub will respond by sending up new stems from its roots in spring. Those new stems often grow to be 18 inches or 2 feet tall by early summer.
“It may take a couple of years for the shrub to regain its full height,” Yiesla said. “But the technique can save some gnarly, messy old plants that you might otherwise give up on.”
Once a shrub is rejuvenated, keep up with the pruning each year to make sure it doesn’t become another tangled mess. Remove some of the oldest, thickest stems regularly to make space for new growth.
Just make sure that in any year, you don’t remove more than one-third of any shrub’s branches overall. Let it keep enough stems to bear the leaves it needs to collect the energy that fuels its growth.
Midwinter is a good time to prune deciduous shrubs — those that lose their leaves in fall — because it’s easy to see the structure and judge which branches to remove. For evergreen shrubs, which keep their leaves or needles in winter, wait until spring to prune.
Most shrubs are best pruned selectively, using hand pruners, rather than with a power tool. Take out only those branches that need to go in order to control the shrub’s size, maintain a nice, natural shape, and keep it uncrowded so air can circulate freely. Hand pruning will keep most shrubs more attractive and healthier.
There are several pruning techniques, and rejuvenation pruning is not the right one for every kind of shrub. It works best on vigorously growing species such as forsythia, weigela, privet, honeysuckle, spirea and some kinds of hydrangea. To learn about the right kind of pruning for different shrub species, see mortonarb.org/pruning-deciduous-shrubs.
Be aware that if you rejuvenate a spring-flowering shrub such as lilac or forsythia, it will cost you one year’s bloom. You will be removing the flower buds along with the stems. The new stems that sprout this spring will not develop flower buds in time to bloom this year. Instead, they will develop buds this fall to bloom next spring.
Usually, it’s worth the sacrifice of a year’s flowers. “An old, crowded shrub often doesn’t bloom much anyway,” Yiesla said. “The dense mass of branches shades out many of the buds, and generally old wood doesn’t bloom as vigorously as new wood.”
Rejuvenating the shrub to make room for vigorous new growth, and keeping it pruned every year to make room and give sunshine to those younger stems, will help it bloom better in many spring-times to come.
For tree and plant advice, see the online resources of The Morton Arboretum at mortonarb.org/plant-care, or submit your questions online at mortonarb.org/plant-clinic or by email to
plantclinic@mortonarb.org. Beth Botts is a staff writer at the Arboretum.