Shrub Maintenance and Renewal Pruning

Shrub maintenance and renewal pruning keep a tired border bushy and in flower, because the right cut on old wood turns a leggy shrub into a young one.

Most shrubs can be kept dense and flowering with one cut a year, made at the right time. The right time depends on whether the shrub flowers on last year’s wood or on this year’s growth, and overgrown plants are best renewed by removing the oldest third of the stems each year for three years. This guide covers timing by flowering group, the rule of thirds, hard rejuvenation and the plants that can’t take it.

It belongs to the Trees guides and leaves cut technique and tool choice to How to Prune Trees Safely. Aftercare is covered in Tree Watering & Mulching.

Shrub pruning at a glance

Prune by flowering time

Pruning at the wrong moment is the most common reason a healthy shrub fails to flower. Buds that will open next spring form the previous summer on old wood. Cut that wood in winter and you cut the flowers.

In regions with hard late frosts, delay cutting new-wood shrubs until the worst cold has passed, because regrowth stimulated by a mild spell can be burned. In frost-free climates, summer-flowering shrubs can be cut at the end of their dormant or dry period instead.

The rule of thirds

For multi-stemmed shrubs that have become tall, bare at the base and flowering only at the tips, renew them gradually instead of in one drastic cut. The plant keeps its leaves, so it keeps feeding itself, and you keep most of its flowers.

1. Pick the right moment for the shrub’s flowering group, as in the table above.
2. Remove dead, diseased and damaged stems first, cutting back to healthy wood or the base.
3. Identify the oldest stems. They are the thickest, greyest, most deeply barked and usually most heavily branched. Pick about one third of the total.
4. Cut them to 5 to 10 cm above ground, just above a bud or low shoot where one exists. Use loppers or a pruning saw for stems above 2 cm.
5. Thin out crossing and inward-facing shoots so light reaches the centre.
6. Repeat in the next two years, each time taking the oldest remaining third.

Count stems before you start. A shrub with nine main stems loses three each year, which feels timid on day one and looks well proportioned by year three. Anything that has not sent up a few strong new shoots by midsummer is probably not suited to the process.

Hard renewal: who survives it

Hard renewal cuts the whole shrub to 15 to 30 cm in one go. It works only where the plant has dormant buds low down in old wood, and it costs you a year or two of flowers. Do it in late winter for new-wood shrubs and just after flowering for old-wood shrubs, even though you sacrifice the next display.

For plants in the middle column, stage the work: cut half the shrub one year and half the next, and expect no flowers for a season. For the last column, replacement is usually better than renewal. A leggy lavender can be trimmed lightly each year to prevent the problem, but once bare wood dominates, a new plant is quicker.

Safety and nesting

Check shrubs for nests before cutting. In many countries wild birds’ active nests are legally protected, and spring to late summer is the main nesting window. Check local rules and, if a nest is present, delay the work. Wear gloves and eye protection, since some shrubs have thorns (berberis, pyracantha) or irritant sap (euphorbia, some privet berries are poisonous if eaten).

Shaping a shrub as it grows

Renewal is much easier if the shrub is shaped while young. In the first two or three years after planting, remove only dead or crossing stems and shorten any lopsided shoot, so the plant branches from low down. Heavy early cutting delays flowering and gains nothing.

Once established, a yearly 10-minute check is enough:

• Remove dead, broken or diseased wood at any time of year.
• Take out one or two of the oldest stems at the base, which is a gentle form of the rule of thirds.
• Cut out any stems that rub across one another, since the wound lets disease in.
• Remove suckers that come from below the graft or from the roots, pulling or cutting them flush at their origin.
• Cut back reverted shoots on variegated shrubs. All-green stems on a variegated plant are stronger and will take over if left.

Hedging shrubs follow a different pattern. Trim formal evergreen hedges a few times in the growing season, and keep the base wider than the top so light reaches the lower foliage.

Aftercare and what to expect

After renewal pruning, regrowth draws on the root system. Spread 5 cm (2 in) of compost or bark mulch over the root zone, kept clear of the stems (see Tree Watering & Mulching), and water every 7 to 10 days in dry weather through the first summer. Avoid heavy nitrogen feeding, which promotes soft growth that’s prone to frost and aphids. A balanced slow-release feed in spring is enough.

Fresh shoots should appear within three to six weeks of a hard cut in spring. If nothing has moved by midsummer, scratch a stem with a thumbnail. Green means alive; brown and dry means that stem is finished. Don’t cut more, and leave the plant for a second season before deciding.

Troubleshooting

Why shrub renewal pruning works

Cutting a third of the oldest stems on forsythia, lilac and dogwood to the base encourages fresh shoots and improves flowering. Sharp secateurs and loppers prevent the ragged cuts that invite canker and fungus. Hydrangea and buddleia respond to different cuts, so you’ll want to check whether they flower on old or new wood before pruning.

Spring-flowering shrubs set buds the previous summer, which means pruning in winter removes the flowers you’d enjoy. Mulch and compost feed the roots after a hard cut and hold moisture while the shrub regrows. Privet and yew tolerate hard renewal, while lavender and rosemary often fail to regrow from bare wood and need lighter trims. How do you know a shrub is overdue? Thin, woody growth and fewer blooms signal that a renewal cut will boost vigour. Shears suit hedges, but a hedge of box or yew still needs occasional deeper cuts to stay dense.

Why shrub maintenance and renewal pruning work

Removing a third of the oldest stems of forsythia, lilac and dogwood at the base encourages fresh shoots and improves flowering within 1 or 2 seasons. Sharp secateurs and loppers prevent the ragged cuts that invite canker and fungus. Hydrangea and buddleia respond to different cuts, so you’ll need to check whether they flower on old or new wood before you prune.

Spring-flowering shrubs set buds the previous summer, which means winter pruning removes the flowers you want. Compost and a mulch layer of 5 cm feed the roots after a hard cut and hold moisture while the shrub regrows. Privet and yew tolerate hard renewal to 30 cm, while lavender and rosemary often fail to regrow from bare wood and need light trims after flowering. Thin, woody growth with fewer blooms signals that a renewal cut will boost vigour, and a feed of potash supports flower buds the following year. Shears suit hedges of box and yew, but even these need an occasional deeper cut to stay dense. A local nursery or your extension service can confirm timing for your shrub, and the tree pruning guide covers the cuts.

You should prune lilac and forsythia right after flowering, because new buds form on shoots made within 8 weeks. Hydrangea and buddleia need different cuts, so check the variety first, and a feed of potash supports bloom. Mulch 5 cm deep holds moisture and reduces drought stress after a hard cut, and secateurs must stay sharp to avoid ragged wounds that attract fungus. Rose and clematis need hard pruning in late winter, and compost around the base feeds the new stems for 3 to 4 months.

Compost feeds new stems after pruning and mulch holds moisture, so hydrangea and rose recover within 6 weeks. Aphid attracts ladybird to fresh shoots of lilac, and a jet of water controls light attacks within 3 days.

Common mistakes

• Pruning every shrub in winter. Spring-flowering shrubs lose their buds. Fix: sort shrubs by flowering group and prune old-wood shrubs after bloom.
• Shearing into a ball. Cutting all tips equally thickens the outside and starves the middle, which turns bare. Fix: thin by cutting selected stems to their base or a side shoot.
• Cutting everything in one session on a sensitive plant. Lavender, heather and conifers rarely recover. Fix: check the tolerance table first and replace instead.
• Leaving stubs. Long stubs die back and invite disease. Fix: cut 5 mm above a bud or flush to the parent stem or ground.
• Using blunt or dirty tools. Crushed wounds heal slowly and spread disease. Fix: sharpen blades and wipe with alcohol between plants if disease is present.

If your loppers struggle with old stems, Best Pruning Tools and Loppers explains when to move up to a saw.

Next steps

Check cut technique and tool care in How to Prune Trees Safely, learn How to Plant a Tree Properly for replacements and see Tree Diseases: Identification and Organic Treatment if dieback persists. Back to Trees.