How to Prune Overgrown Shrubs in Canada
Two ways to bring back a shrub that has outgrown its space: slowly over three years, or all at once in one spring.
How to prune overgrown shrubs comes down to two methods. Renewal pruning removes a third of the oldest stems each year for three years. Rejuvenation pruning cuts every stem to near the ground in early spring and lets the shrub start again.
Both work only on multi-stemmed shrubs that send up new shoots from the base. Neither works on a pine, a juniper or a rhododendron.
Overgrown shrubs at a glance: renewal: each year, cut up to one-third of the oldest, thickest stems to the ground; repeat for about three years. Rejuvenation: in early spring, while dormant, cut all stems to about 10–25 cm. Suits spirea, forsythia, potentilla, smooth hydrangea and many viburnums. Not for pine, juniper or broad-leaved evergreens.
Just need a date? See When to Prune in Canada for when to prune each plant.
Renewal Pruning: A Third a Year
The University of Minnesota Extension describes renewal pruning this way: every year, remove up to one-third of the oldest, thickest stems, right down to the ground. New stems grow from the roots to replace them. Once no thick, overgrown stems are left, switch back to ordinary pruning.
The shrub keeps its size and keeps flowering while you work, which makes renewal the better choice for a shrub in a prominent spot.
Rejuvenation Pruning: All at Once
For a multi-stemmed shrub that is badly overgrown, Minnesota says to cut all the canes back as close to the ground as possible in early spring. You lose that year’s flowers, but within one growing season the shrub looks like a new planting. Wisconsin gives a height of about 10–25 cm from the ground, done while the shrub is dormant.
| Shrub | Rejuvenation? | Source |
|---|---|---|
| Spirea | yes | Minnesota; Wisconsin (Japanese spirea) |
| Forsythia | yes | Minnesota |
| Cane-growth viburnum | yes | Minnesota |
| Honeysuckle | yes | Minnesota |
| Potentilla | yes | Wisconsin |
| Smooth (Annabelle) hydrangea | yes | Wisconsin |
| Butterfly bush | yes | Wisconsin |
Which Method to Choose
| Renewal | Rejuvenation | |
|---|---|---|
| Time to finish | about three years | one season |
| Flowers lost | few | that year’s |
| Looks | stays full | bare for a few weeks |
| Best for | shrubs in plain view, older lilacs | tough, fast shrubs such as spirea and potentilla |
If you are unsure how vigorous a shrub is, use renewal. It is the gentler of the two. See when to prune lilacs for that plant.
Shrubs Not to Cut Back Hard
Wisconsin says broad-leaved evergreens such as rhododendron should not be cut back into older, leafless wood, because they lack the buds to regrow. The same applies to junipers. Pines produce new shoots only at the tips of the current year’s growth, so a pine cut back hard will not recover. See when to prune evergreens.
When to Do It
Early spring, while the shrub is still dormant, suits both methods. For spring-flowering shrubs on the renewal method, Wisconsin’s timing for flowering shrubs still applies: right after bloom keeps more of next year’s flowers. Do not do either in fall. See what not to prune in fall.
Frequently Asked Questions
How do I prune an overgrown shrub?
Either remove up to a third of the oldest stems to the ground each year for about three years, or, for tough multi-stemmed shrubs, cut all the stems to about 10 to 25 cm in early spring.
Can I cut a shrub right down to the ground?
Many multi-stemmed shrubs, such as spirea, forsythia, potentilla and smooth hydrangea, recover well. Evergreens such as pine, juniper and rhododendron do not.
When is the best time to cut back an overgrown shrub?
Early spring, while it is still dormant.
Will my shrub flower after hard pruning?
Not that year in most cases, but within one growing season the shrub should be full again.
How do I bring back an old lilac?
Use renewal pruning: take out a third of the oldest stems each year, right after flowering, for about three years.
Can I renew an overgrown juniper?
No. Junipers do not regrow from bare wood. Prune only the tips, in summer.
Sources
- University of Minnesota Extension — Pruning trees and shrubs (reviewed 2026)
- University of Wisconsin–Madison Extension — Pruning Deciduous Shrubs
- University of Wisconsin–Madison Extension — Pruning Evergreens