How do I prune a shrub?

The general principles of pruning — what to cut, where to cut, and the timing rule that determines whether you get flowers next year.

Difficulty: intermediate
Time: 1 hr 30 min
Read: 3 min
Safety: caution

Short answer

Remove dead, damaged and crossing branches first — that's most of the job on most shrubs. Cut just above an outward-facing bud at a slight angle. The timing rule: prune spring-flowering shrubs just after they flower, and summer-flowering shrubs in late winter or early spring.

Pruning intimidates people because it's irreversible, but the general principles cover most shrubs. The one that catches people out is timing: shrubs that flower in spring have already formed those buds the previous year, so a winter prune removes the flowers you were waiting for.

Safety

Wear eye protection when pruning at head height — springing branches are a common cause of eye injury. Keep secateurs sharp, since blunt blades slip. Do not prune anything requiring a ladder or a chainsaw yourself; that's a job for someone equipped for it. Check for nesting birds before cutting anything between spring and late summer — disturbing an active nest is illegal in the UK.

What you'll need

Sharp secateurs
Loppers for thicker stems
Pruning saw for anything over about 3cm
Gloves and eye protection
Disinfectant for blades (optional)

Step by step

Identify when the shrub flowers before cutting anything.Spring-flowering (forsythia, philadelphus, weigela) flower on last year's wood. Summer-flowering (buddleia, most hydrangeas, late clematis) flower on this year's.
Prune spring-flowering shrubs immediately after they finish flowering.This gives them the whole season to make next year's flowering wood.
Prune summer-flowering shrubs in late winter or early spring.They'll produce the flowering growth in the same season, so there's nothing to lose.
Start with the three Ds: dead, damaged and diseased.On a neglected shrub this is often the entire job and it improves both health and appearance.
Remove crossing and rubbing branches next.Rubbing wounds the bark and lets disease in. Take out the weaker of any crossing pair.
Thin out congested growth to open the centre.Airflow through the middle of a shrub reduces fungal disease considerably.
Cut just above an outward-facing bud, at a slight angle sloping away from it.The new shoot grows in the direction the bud points, so outward-facing buds keep the centre open.
Don't remove more than about a third of the plant in one season.Hard renovation is possible for some shrubs but stresses the plant. Spread it over two or three years where you can.
Clean blades between plants if you're cutting anything diseased.Secateurs spread disease efficiently between plants.

Tips

When in doubt, do nothing and watch the plant for a year. Learning when it flowers is worth more than an early prune.
Sharp secateurs make a clean cut that heals; blunt ones crush the stem and invite disease. Sharpen or replace them.
Don't leave stubs. Cut back to a bud, a branch junction, or the base — a stub dies back and can rot into the plant.
Nesting birds are protected in the UK. Check thoroughly before cutting hedges and shrubs between March and August.

Common mistakes

Pruning spring-flowering shrubs in winter — You cut off the flower buds formed last year, so it doesn't flower.
Cutting too far above a bud — The stub dies back and can allow rot into healthy wood.
Removing too much at once — Severe pruning stresses the plant and often triggers a mass of weak regrowth.
Pruning hedges during nesting season without checking — It's illegal in the UK to damage or destroy an active nest.

Questions people ask

When should I prune?

It depends on when the shrub flowers. Spring-flowering: straight after flowering. Summer-flowering: late winter or early spring. If you don't know, watch it for a year first.

How much can I cut off?

As a general rule, no more than a third in one season. Some shrubs tolerate hard renovation, but staging it over two or three years is safer for most.