When to Prune Flowering Shrubs in Canada
One question decides the date: does the shrub flower on last year’s wood or on this year’s? Get it wrong and you cut off next spring’s flowers.
When to prune flowering shrubs in Canada depends on when the shrub makes its flower buds. Spring bloomers such as forsythia, lilac and weigela set next year’s buds in summer, so you prune them right after they flower. Summer bloomers such as potentilla and Japanese spirea flower on new growth, so you prune them in late winter, before the buds break.
Prune a spring bloomer in fall or in March and the shrub still grows, but it flowers poorly the next year, because the buds you cut off were the flowers.
Flowering shrubs at a glance: spring bloomers (forsythia, lilac, weigela, mock orange, viburnum, early spirea): prune right after flowering. Summer bloomers (potentilla, Japanese spirea, rose of Sharon, panicle and smooth hydrangea): prune in late winter or early spring, before bud break. Shrubs grown for leaves (ninebark, dogwood, burning bush): spring, before growth.
Looking for one plant? See When to Prune in Canada for every common Canadian plant in one table.
Old Wood or New Wood
The University of Wisconsin–Madison Extension puts it simply. Spring-flowering shrubs form flower buds on one-year-old wood, the stems that grew the summer before, so they are pruned after they flower and before next year’s buds are set. Summer-flowering shrubs form buds on new growth in spring, so they are pruned while dormant or in early spring, before bud break. Wait until late spring to prune a summer bloomer and you cut off its flower buds instead.
| Group | Examples | When to prune |
|---|---|---|
| Spring bloomers (old wood) | forsythia, lilac, weigela, mock orange, viburnum, chokeberry, early spirea, magnolia, flowering plum and cherry | right after flowering |
| Summer bloomers (new wood) | potentilla, Japanese spirea, rose of Sharon, panicle and smooth hydrangea, smokebush, shrub roses | late winter or early spring, before buds break |
| Grown for foliage | ninebark, dogwood, burning bush, barberry, alpine currant, sumac, peashrub, purpleleaf sandcherry | spring, before growth starts |
The groups are drawn from the University of Wisconsin–Madison and University of Minnesota extension lists. Smokebush appears in both the summer-flowering and the foliage list; either way, it is pruned in spring.
Spring Bloomers: Right After the Flowers Fade
Forsythia, lilac and weigela finish flowering in late spring. Prune in the weeks right after, while the stems that will carry next year’s flowers are still growing. The University of Minnesota lists apricot, azalea, chokeberry, chokecherry, clove currant, flowering plum, flowering cherry, forsythia, juneberry, lilac, magnolia and early-blooming spirea in this group.
Wisconsin adds that spring bloomers which sucker from the base, such as forsythia and lilac, do best with thinning: take a few of the oldest stems right down to the ground rather than shearing the top. For each plant, see when to prune lilacs and forsythia in Ontario.
Summer Bloomers: Late Winter, Before Buds Break
These shrubs flower on stems that grow the same spring, so a cut in March costs nothing. Wisconsin says potentilla, Annabelle-type smooth hydrangea and Japanese spirea can even be cut back to 10–25 cm from the ground while dormant when they get leggy.
The University of Minnesota notes that hardier shrubs such as late-blooming spireas and smooth hydrangeas can be cut to the first pair of buds above the ground, while plants with marginally hardy stems, such as shrub roses, should only be cut back to live wood. See how to prune hydrangeas and when to prune rose of Sharon.
Wisconsin also notes that deadheading Japanese spirea can bring a second flush of flowers.
Shrubs Grown for Their Leaves
Ninebark, dogwood, burning bush and barberry are planted for foliage, stem colour or shape rather than flowers. The University of Minnesota says to prune them in spring, before growth begins. There are no flower buds to protect, so the main concern is cutting before the new leaves have used the plant’s stored energy.
How to Cut
Most shrubs should not be sheared. Wisconsin warns that hedge shears remove the natural form, thin out the leaves and flowers inside the shrub and cause a mass of new shoots. Use hand pruners or loppers instead.
To shorten a stem, cut back to a side branch or about 6 mm above an outward-facing bud. To thin, remove a whole stem at its base. Remove no more than about a third of the stems in one year. For a shrub that has outgrown its space, see how to prune overgrown shrubs.
Frequently Asked Questions
When should I prune flowering shrubs in Canada?
It depends on the shrub. Prune spring bloomers such as forsythia, lilac and weigela right after they flower. Prune summer bloomers such as potentilla, Japanese spirea and panicle hydrangea in late winter or early spring, before the buds break.
Why did my forsythia not flower after pruning?
It was probably pruned in fall, winter or early spring. Forsythia sets its flower buds the summer before, so pruning it before it flowers removes those buds.
Can I prune shrubs in the fall?
Not spring bloomers: fall pruning removes next year's flowers. Summer bloomers and foliage shrubs are better left until late winter as well. Dead or broken branches can come off any time.
When do I prune weigela?
Right after it flowers in late spring. Weigela blooms on stems that grew the year before.
When do I prune ninebark?
In spring, before growth begins. Ninebark is grown mainly for its foliage.
Should I use hedge shears on my shrubs?
Only on formal hedges. For most shrubs, the University of Wisconsin-Madison recommends hand pruners or loppers, because shearing ruins the natural form and reduces flowering inside the shrub.
Sources
- University of Wisconsin–Madison Extension — Pruning Deciduous Shrubs
- University of Minnesota Extension — Pruning trees and shrubs (reviewed 2026)