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How to Prune and Look After Buddleja

A short guide to pruning, growing and taking care of this popular garden shrub, also known as the butterfly bush

Houzz UK contributor and award-winning landscape and garden designer. Claudia de… More

Many deciduous summer flowering shrubs such as buddleja, or butterfly bush, can be pruned now (as long as temperatures are above freezing and frost is no longer a threat) as they flower on this year’s growth. Annual pruning encourages new strong growth and bigger blooms for the coming year. Below is a short guide on how to look after this nectar-rich shrub.

For more in this series, scroll to the end of the story.

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Which variety should you choose?
Buddleja bushes produce lovely conical flowers that appear on graceful, arching stems with feathery silver foliage. They look good as tall plants at the back of a big border, as they’re both fast-growing and easy to cultivate.

There are also many varieties, with some being more suited to smaller gardens and areas where a more compact shrub is needed. Make sure you buy the correct variety for the area you wish to plant.

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If you have the space, there’s a wonderful sapphire blue variety called ‘Blue Horizon’ that can grow to 3m (10ft) tall. If you like dark purple, opt for ‘Black Knight’, which has a very long flowering season. Buddleja davidii ‘Summer Beauty’, which is similar in colour to this image, is a compact shrub suitable for the front of a border.

For an even more compact variety with shorter panicles of flowers, opt for the lovely purple Buddleja davidii ‘Buzz Sky Blue’. This blooms later in the year.

If yellow is your colour, try Buddleja x weyeriana ‘Sungold’, which has the added benefit of a strong fragrance, and Buddleja globosa, which has orange/lemon ball-shaped flowers and is slow-growing and non-invasive, so suitable for a low-maintenance garden.

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Why cut back?
Buddleja can easily get leggy and out of hand, especially if not pruned hard in the spring. You’ll often see buddleja plants on railway embankments or growing out of the top and sides of buildings, looking very straggly. These plants have self-seeded and can look like a tall, tangled mess, with flowers only held at the tip.

This is what you want to avoid in your garden. So the main aim of cutting back a buddleja is to have a strong framework of branches and to maintain the plant’s vigour. The common Buddleja davidii is almost indestructible. Aim to leave five to six branches; these, in the end, will resemble a stag’s antlers.

Don’t get too worried if the plant looks as if it’s dead, as the new green growth is produced from underneath the bark. Buddleja flowers off the new season’s growth. Make sure you don’t prune when the weather is below freezing or there’s a hard frost expected, as the cut ends will die.

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How much should be pruned?
To start pruning your plant, remove the top growth by half; this will allow you to see the structure beneath a lot easier. Once the top growth has been removed, start by cutting through the thick woody stems to just above a bud at a slight slant. Stems that carried last year’s blooms are pruned to leave two buds above the older, darker growth below. Aim to leave a plant of about knee height. After pruning, mulch the base of the plant with mushroom compost.

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What’s the best way to grow buddleja from cuttings?
If you wish to take softwood cuttings of your plant, the best time to do this is in the spring. Remove stems that are around six inches long to just below the leaf node and nip out the top of the cutting.

Plant your cuttings into a mixture of half compost, half horticultural sand and remove any large leaves. Water your cuttings and cover with polythene or place under glass. You will soon have small plants.

Buddleja thrive in sunny positions and love thin, chalky soils, but they don’t do well in soil that retains water in the winter.

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What about deadheading?
This, of course, comes later in the year. There are several reasons to deadhead. Firstly, as buddleja seeds blow away easily in the wind, they may end up in a part of the garden where you don’t want them, so keeping on top of deadheading should help.

Secondly, the faded blooms look brown and messy, detracting from the look of the shrub, so it’s a good idea to remove any flowers that have faded and gone over throughout the flowering season.

Deadheading spent blooms will stimulate a continuous supply of flowers, plus it stops the plant from ripening the spent flower into seeds, thus directing its energy into making more flowers.

How to do it? Using a pair of secateurs, remove the dead blooms back to a leaf. Try to cut the faded flower between two side branches, as these will be the new flowering buds. Sometimes, the side branches themselves carry brown and crispy flowers. If this is the case, cut the whole stem back to the next branching node on the stem.

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Will buddleja attract insects?
Buddleja is a wonderful plant for attracting butterflies and moths to your garden, as the flowers are nectar-rich and only accessible to insects with a long ‘tongue’.

Many hybrids of Buddleja davidii do not have as much nectar as the species plants, so choose the more common varieties to attract butterflies. Also, try to plant some nettles nearby – perfect in a wild area of the garden or a hidden patch beside a shed. Nettles attract the larvae of the red admiral, small tortoiseshell, peacock and comma butterfly.

Further reading

  • How to Prune and Look After Wisteria
  • How to Look After Your Hedges – 8 Pruning and Maintenance Tips
  • A Beginner’s Guide to Pruning
  • When Should You Prune Your Grape Vine?
  • When is the Right Time to Prune Your Hydrangeas?
  • How to Deadhead Roses and Other Popular Plants

Tell us…
Do you have pruning tips to share? Let us know in the Comments section.

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