Buddleja in bloom

How to prune buddleja and shrubs

Our guide to successful pruning buddleja from plantsman John Hoyland who looks at cutting back flowering shrubs to achieve a well-shaped prolifically flowering plant. Photographs Gavin Kingcome

When to prune buddleja and shrubs

The more a plant enhances the garden, the more nurturing it needs. Shrubs with exuberant flowers need regular attention to continually be at their best and an important part in their care is pruning. There are few rules about what to prune when, and there are always exceptions. One guide is to prune as long before the shrub flowers as possible. Some shrubs flower on stems that have grown during the current year, others on stems that were formed during the previous season.

Advertisement
Cut stems just after a bud
© Gavin Kingcome

The time of year a shrub flowers, and the age of the stem on which it flowers, will determine how it should be pruned. Regular pruning of flowering shrubs will keep the plant to an attractive shape and will encourage large, healthy flowers. In general, pruning is only necessary for mature shrubs, so wait a year or two after planting before starting to prune. Shrubs that flower on the current season’s growth tend to flower in late summer or autumn.

The ideal time to prune these is during the winter or early spring.

How to prune

The stems of the butterfly bush, Buddleja davidii, should be cut right down to the base, leaving a woody clump. Cut just above the first shoot at the bottom of the stem. Even by the end of a single season the stems can be thick and woody, so you will need loppers or a pruning saw rather than a pair of secateurs. After cutting back all the stems you will be left with an unattractive stump, but not cutting it back could result in a shrub 3m tall with a solitary flower at the tip, similar to those found on railway embankments. The Russian sage, Perovskia atriplicifolia, should be treated similarly, but waiting until late spring to do it will lessen the chance of frost damage to shoots. The majority of shrubs that flower on new growth are not as vigorous as Buddleja or Perovskia, and cutting back all the stems can leave a shrub looking thin and weedy. The best strategy is to remove about a third of the stems by cutting them down at the base.

Buddleja alternifolia should be pruned after flowering by cutting stems down to just above a new shoot
Buddleja alternifolia should be pruned after flowering by cutting stems down to just above a new shoot

If you are unsure how much of the shrub to cut down, err on the side of caution, cutting back fewer stems. Hydrangea paniculata, for example, can end up as an ugly stump if all of it is cut down continually. Cut any dead, overcrowded and thin stems back to the base, but cut back the flowered stems to the next bud.

Variations

Not all plants in a genus should be pruned the same way. Buddleja alternifolia, for example, flowers on stems that have grown the previous year, so removing these stems in the spring would leave you with no flowers. As soon as its flowers have died, follow down along the stem and cut just above a new shoot.

Prune Buddleja davidii just above the first shoot at the base of the stem for best results.
Prune Buddleja davidii just above the first shoot at the base of the stem for best results.

Cistus, the sun rose, and Convolvulus cneorum also flower on previous-season growth. These are shrubs that will continue flowering and maintain a neat shape without any pruning. However, vigorous new shoots produce the most flowers, while older branches produce few or none at all. Removing flowering shoots just after they have flowered will stimulate the plant to produce more flowers. Cut the flowered stems off just above a bud about a half to two-thirds down the stem. It won’t have a dramatic impact on the shape of the shrub, but you will have more flowers the following year. Some flowering shrubs do not benefit from annual pruning. Witch hazels and viburnums are best left alone, although every three or four years you can remove some branches to prevent the shrub from becoming overcrowded. Do this after flowering and cut back the branches to the base or to the joint of another branch. Remove any dead branches too.

Buddleja davidii must be cut back harshly to a stump to ensure the most attractive growth pattern and avoid leggy, tall shrubs with few flowers.
Buddleja davidii must be cut back harshly to a stump to ensure the most attractive growth pattern and avoid leggy, tall shrubs with few flowers.

The straggly Buddleja davidii needs to be cut right back using hefty loppers to get through the woody stems.

Shrubs that flower on new growth
Buddleja davidii
Clerodendrum bungei
Diervilla
Hydrangea paniculata
Philadelphus
Spiraea x bumalda
Spiraea japonica

Practical Advice

How to sharpen secateurs

  • Don’t go near a shrub with blunt secateurs.
  • Cuts must be crisp and clean so you need a sharp blade.
  • Carry a small sharpening stone in your pocket and you can sharpen your secateurs regularly.
  • Little and often are the watchwords.
  • Draw the cutting edge of the blade firmly and slowly five or six times over the stone at an angle of about 30°, with the bevelled edge of the blade downwards. Pass over the other side of the blade once to remove any fragments of metal.
  • Get into the habit of doing it often and your secateurs will stay sharp.

Read our full guide on how to sharpen your gardening tools.

Shrubs that flower on previous-season growth

Buddleja alternifolia
Buddleja globosa
Buddleja colvilei
Deutzia, Exochorda
Forsythia, Ribes
Spiraea ‘Arguta’
Spiraea thunbergii
Spiraea veitchii
Weigela Flowering 

Renewing old shrubs

Shrubs that have been neglected and left unpruned will develop into a scraggy mass of branches with few flowers, or a tall lanky shrub with bare stems and miserable flowers out of sight at the top. If you’ve let a shrub get into such a state, or you’ve inherited one, don’t despair. You can bring it back to its former, happier self with these easy steps.

  • Completely removing any dead branches.
  • Take out branches that are growing across the shrub and any that are rubbing against each other. Aim for an open structure that the air and light can get into.
  • Cut down the shrub by two-thirds. Drastic, but beneficial.
  • In the year following such severe treatment the plant will put its energy into producing new shoots, so you won’t get many flowers.
  • Pruning shrubs in this way can be done at any time of year. With deciduous shrubs it’s easier to do it in early winter, after the leaves have fallen, so that you can see clearly what you are doing.
buddleja_4.tif
© Gavin Kingcome
Advertisement

Not all shrubs respond to this treatment. Daphne, Genista and Cytisus (except C. battandieri) will not re-grow from mature, woody stems. In general, if you see dormant buds on old stems, the shrub will re-grow. Rhododendrons will respond to hard pruning but, remember, the buds will be hidden under the bark.

Shrubs that require minimal pruning

Amelanchier
Callicarpa
Hamamelis
Magnolia
Syringa
Viburnum