Gardens Illustrated
Photo showing the large purple flowers of a buddleia tree growing in the wild (Latin name: Buddleja davidii). This is also known as a 'butterfly bush', as the extremely fragrant flowers are often covered in colourful peacock butterflies.

How to prune shrubs

Published: June 27, 2022 at 8:42 am
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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

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.

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When to prune shrubs

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.

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 shrubs including buddleja

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

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.

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.

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.

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

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

Don't miss our round up of the best pruning 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 

Pruning 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.
© Gavin Kingcome
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Not all shrubs respond to this treatment. Daphne, Genista and Cytisus (except Cytisus 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

Authors

A former nurseryman, John now spends most of his time nurturing his own garden in the foothills of the French Pyrenees. He is Gardens Adviser to Glyndebourne and currently has gardening projects in the UK, Spain and France.

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