Flowering shrubs bring your landscape year-round beauty. Their pollinator-friendly blossoms and scents herald changing seasons and set your property apart. Add ornamental fruits and colorful stems that many flowering shrubs deliver, and you have a winning combination from the start … if your pruning is spot-on.
To look and perform their best, flowering shrubs need regular pruning. But pruning pointers for blooming shrubs differ from tips for trees and evergreens. Success depends on knowing what to prune, how to prune it and, perhaps more importantly, when to prune. Timely, proper pruning can help your landscape’s flowering shrubs live up to your bloom-filled dreams.
Understanding Flower Buds and Shrub Growth
Before you pick up your pruners and start chopping at suckers, you need to understand that all flowering shrubs aren’t created equal. Plants in this group fall into one of three important categories:
- Early-blooming shrubs that flower in spring.
- Late-blooming shrubs that flower in summer.
- Remontant or “everblooming” shrubs that bloom in spring and summer.
Professor John Ball, South Dakota State University Extension Forestry Specialist and South Dakota Department of Agriculture Forest Health Specialist, explains that early blooming, spring-flowering shrubs bloom from flower buds that formed on stems during the previous summer. Long before you can see them, these summer-forming buds are there, ready to endure winter and bloom in spring.
If you’ve heard gardeners talk about shrubs that bloom on “old wood,” this is what they were referring to. These spring-blooming shrubs include long-standing favorites such as lilac, forsythia, rhododendron and old-fashioned mophead hydrangea.
Late-blooming, summer-flowering shrubs form their flower buds on new growth, those stems grown in the same year that they flower. This is what’s referred to as “new wood.”
Shrubs that bloom on new wood, such as spiraeas, potentillas and smooth hydrangeas, can die back from winter cold or hungry critters and grow new stems that yield bountiful blossoms come summer. Ball explains that, left to age without pruning, these shrubs become filled with old, unproductive, sporadic-blooming stems.
Recent years have seen plant breeders focus on “everblooming” shrubs, particularly hydrangeas, that bloom on old wood in spring and produce summer flowers on new wood in the same growing season. For these remontant types, Oregon State University recommends limiting your pruning to minimal shaping to keep old and new wood intact for blooms.
|How, When to Prune Typical Types of Flowering Shrubs|
|Flowering Shrub Type||Examples||When to Prune||How to Prune|
|Spring-blooming shrubs (bloom on old wood)||Lilacs, forsythias, azaleas, weigelas, traditional bigleaf hydrangeas||Prune immediately after they finish flowering in spring.||Remove one-third to one-fifth of the oldest stems every two to three years. Prune those oldest stems back to 2 inches above ground level.|
|Summer-blooming shrubs (bloom on new wood)||Smooth and panicle hydrangeas, diervilla (bush honeysuckle), potentillas||Prune during late-winter dormancy, right before spring bud break.|
|Everblooming shrubs (bloom on old and new wood)||Remontant or reblooming shrubs, such as Endless Summer hydrangeas||If you prune, prune right after spring flowering (the biggest flush of flowers) finishes.||Limit pruning to a minimum for maximum flowering. Thin and shape only as needed.|
Timing Your Pruning to Encourage More Flowers
When your pruning objective is to improve on the number and quality of your shrub’s blooms, Ball suggests maintenance pruning every two to three years. Pruning shrubs at the proper time of year is critical for flower growth.
Prune spring-flowering shrubs right after they finish flowering, before next spring’s all-important flower buds form. If you prune early bloomers in fall or winter — after their flower buds form in summer — you’ll remove all the buds that would have bloomed the next spring.
For summer-blooming shrubs, you want to time your pruning to stimulate new flower-bearing growth. Ball says that the best time for this is late winter, right before buds break in spring.
For smaller, multi-caned blooming shrubs up to about 6 feet high, Ball recommends removing one-third of the canes every two to three years. For larger blooming shrubs — up to 15 feet tall, for example — remove just one-fifth of the canes. This will keep enough young wood on the plant to encourage blooms from base to top.
For shrubs with vibrant stem color, such as red- or yellow-twig dogwoods, prune to promote the intense color that occurs on new growth. By enjoying the stems through winter, then pruning back after spring blooms, stem colors intensify through the season to hit their peaks in winter months.
Another consideration is ornamental fruit, which can help make your landscape a haven for birds and other wildlife. Fruit develops from flowers, so anytime you prune flowers or flowering stems, you’ll sacrifice the year’s fruit that would have followed.
If your shrub has dead or damaged stems, remove them any time. But if you suspect disease, Ball recommends waiting until winter when the plant — and the disease — are in their dormant season. There’ll be less chance you’ll unwittingly spread the disease.
Prune Shrubs for Renewal or Rejuvenation
When your flowering shrubs haven’t been maintained regularly, they may need more extensive pruning to get back in flowering form, regardless of their flowering category. This approach to overgrown shrubs takes two primary avenues:
- Renewal pruning.
- Rejuvenation pruning.
Ball explains that renewal pruning involves gradually removing all the stems over a period of three to five years. Unless shrubs are heavily overgrown, this is the best approach.
Each year, remove one-third to one-fifth of the largest, oldest stems. As with regular pruning, the larger the shrub, the smaller the amount removed each year through these thinning cuts. This gradual process restores your shrub’s beauty and flower-producing potential. By project end, all the stems have been renewed.
For shrubs that are seriously overgrown or display poor flowering, more dramatic rejuvenation is in order. With rejuvenation pruning, the entire plant is cut back at once.
For some dense, low-growing, flowering shrubs, such as spiraeas and potentillas, Ball recommends this approach every three years in late winter or very early spring before bud break. These smaller, low-growing shrubs will come back and bloom profusely the same summer.
Larger shrubs, such as neglected overgrown lilacs, can also be rejuvenated in this way. But take heed, they’ll take several years to recover and bloom again.
Ball warns that this advice only applies to blooming shrubs with numerous canes. Don’t try this with tree-like shrubs with few stems or evergreens, such as yews or arborvitae. These plants lack the ability to sprout new stems in the same way. Instead, treat those plants as trees and follow guidelines for tree pruning, removing individual side branches rather than full stems.
If you lack the patience or the purpose for renewal or rejuvenation, you may want to remove overgrown shrubs. Take out the whole plant, including roots, and plant new specimens. Then be sure to stay on top of regular pruning to prevent the problem from arising again. If you’re replacing, be prepared for an extensive root system on large, old shrubs.
Making the Proper Cut
Unlike trees, most flowering shrubs grow long, cane-like stems with little significant branching. Ball says the best way to maintain an attractive, natural-looking, flowering shrub is to remove entire stems when you prune.
This type of cut — a “heading cut” — takes the stem back to about 2 to 3 inches above ground level. This stimulates numerous new shoots from just below the cut. The result: a plant that has natural form and attractive growth, free from ugly pruning cuts and unnatural shoots high in the plant.
Ball also strongly recommends making heading cuts straight across, not angled. For many years, traditional pruning advice called for angled cuts so water runs from the cut surface. Ball says that current research proves the angle is unnecessary, but there’s another, more powerful reason to make straight, low cuts.
Many homeowners prune woody shrubs to about 2 feet high, an easy height when standing. Ball warns that this practice, combined with angled cuts, creates a serious safety hazard for playing children, pets and adults. He has first-hand knowledge of an extremely serious injury to a child that resulted from high, angled pruning. In addition, shrubs pruned in this manner typically yield few or no flowers below that pruning mark.
Proper Pruning Tools
Proper pruning also calls for proper tools. As a rule of thumb, the North Carolina Cooperative Extension recommends hand-held bypass pruners for small stems less than 1/2 inch in diameter. Ball agrees: Bypass pruning shears, which have scissor-like blades that pass each other, deliver a clean cut that keeps tissue intact so sprouting can occur.
Anvil pruners, which pair one blade with a flat, anvil-like base, crush the stems rather than cut them cleanly. Ball says this hinders the plant’s ability to produce new shoots just below the cut.
For larger stems, up to 1 inch in diameter, bypass loppers provide the added leverage needed for bigger stems. For stems over 1-inch diameter, a pruning saw will do the trick. And, whatever the stem size, avoid using pruning sealers.
By using the proper tools, techniques and timing, you can keep your flowering shrubs at their blooming best — and keep your landscape free of pruning-related hazards, too.