Pruning Primer: Give Your Shrubs a “Prune-Up”
By Laurie Casey
The Morton Arboretum
The time for one of the most useful winter garden chores is upon us. Sharpen your pruners and start inspecting your deciduous shrubs and smaller trees, the ones that lose their leaves in the fall. The next mild day between now and early March, you can begin to re-invigorate and shape them while they are dormant. Pruning helps spur new, vigorous growth and better flowering and fruiting.
First, look for stems that are diseased, damaged, dead or crossing. Look at their overall shapes and sizes, and if they flower, think about how well they flowered this past year.
“Pruning is truly is an art,” said Ronald Picco, horticultural specialist at The Morton Arboretum. “It will take a few years to learn, but each time you prune, observe how the plant reacts.”
Pruning during the dormant season gives several advantages. It puts less stress on the plant, for one. In addition, when the stems are bare, you can see what you are up against in terms of disease or damage, said Picco. If there are diseased stems, in winter there’s little chance of transmitting the diseases as you cut them out, a common problem during the growing season. If you see diseased stems but aren’t sure what’s afflicting them, bring one into the Arboretum’s Plant Clinic for diagnosis.
Another advantage of winter pruning is that you can easily see the structure of the plant, said Picco. Crossing stems, stems growing in awkward directions or redundant branches that grow alongside another one are all good to take out when shaping the plant.
The dormant season is also the best time to do renewal pruning, which helps old, overgrown shrubs create new growth from the base of the plant and increases blooms in those that flower. The rule of thumb is to remove a third of the old stems or canes, down to the base of the plant, each year for three years.
Another pruning technique is shearing, when you trim the ends of an entire shrub. We often shear hedges. If you plan to shear an entire shrub that bears flower buds on the previous year’s growth, such as forsythia, mock-orange, fothergilla, oak-leaved hydrangea or spicebush, do it after spring flowering, according to Picco. If you shear them now in the dormant season, you’ll lose the flower buds that have already formed, causing very sad looking spring flowering.
A common but avoidable reason we prune is to help the plant fit its space. “People have favorite plants they want to use, even though they know they are the wrong plant for the location. So they prune to help the plant fit,” said Picco. You can avoid this extra pruning by moving the too-large shrub to a bigger location, and selecting the right-sized plant for the space.
For more tips and guidelines for pruning specific types of deciduous shrubs, find the free leaflet, “Pruning Deciduous Shrubs” at www.mortonarb.org. Choose “Plant Trees,” then “Plant Clinic.”
Glad You Asked
Q. Can you prune an evergreen like you do a deciduous shrub?
A. There are similarities, but one main difference is that, with a few exceptions, if you prune an evergreen back to the “dead zones” on the stems, where they have no leaves, no new leaves will appear. Deciduous shrubs, on the other hand, will usually grow new leaves on bare stems.
Q. How important is making a clean cut?
A. Be sure your pruners are sharp. Make a clean, slightly angled cut just above the collar, the slight flare where the stem meets another one or the trunk. A flush cut or a jagged edge makes it harder for the plant to heal the wound and invites disease.
At the Arboretum
Learn to shape your trees and shrubs to add polish to your landscaping at “Pruning Small Trees and Shrubs” 1-3 p.m. Saturdays, January 31 and February 7 and 14. Fee is $105 (discount for members). Registration now open. Call 630-719-2468.
Laurie Casey is a staff writer at The Morton Arboretum in Lisle.