Butterfly bush is the everyday name for Buddleja davidii. The shrub flowers from July to September with scented, cone shaped panicles that pull in butterflies, bumblebees and honeybees. The thing to understand is that it flowers on new wood, meaning shoots formed in the same season. That one detail governs how you prune, and it explains why the shrub is cut back hard every spring.
Why spring pruning decides the flowering
The flower buds sit on growth made during the current season, never on last year's wood. Leave old stems standing and the shrub spreads its energy over many weak shoots. You end up with a bush that is bare at the base and carries short panicles high up where you cannot see them. Cut the whole shrub back to 30-50 cm above the ground instead and it makes a few strong shoots, and those are the ones that carry the long panicles.
The month is April. The Royal Horticultural Society gives late March to mid April, that is when the buds have swelled but before the shoots have extended. Never prune in autumn. The cut surfaces die back and you lose the woody framework the shrub shoots from in spring.
How to prune a butterfly bush
Wait for the buds: go out in April and feel where the buds are swelling along the stems. We go by the buds rather than the calendar, because that shows you exactly where the live wood ends.
Choose the framework: keep 3-5 strong stems coming from the base. Remove the rest completely.
Cut back: shorten the chosen stems to 30-50 cm above the ground, just above an outward facing bud.
Clear the base: take out dead, brittle and crossing stems right down at the base so air can move through the shrub.
Mulch: spread 5-7 cm of compost or bark mulch around the shrub after pruning, keeping the material a few centimetres clear of the stems.
The shrub grows back fast. From 40 cm in April to full height and flower in July is normal.
Position, soil and watering
Sun: full sun. In part shade the shoots run longer and the panicles are fewer.
Soil: free draining matters more than rich. A pH between 6.0 and 7.0 suits it. Heavy clay needs opening up with sand and compost.
Water: water regularly through the first season. Once established the shrub is drought tolerant and comes through a dry summer without watering.
Feed: sparingly. Too much nitrogen gives long leafy shoots and fewer flowers.
Wind: avoid exposed sites. The fast grown shoots are brittle and snap easily once the panicles get heavy.
What kills a butterfly bush is almost always wet, cold soil over winter rather than the cold itself. If the spot stands under water in March you need to raise the planting or move the shrub.
Hardiness and overwintering
The shrub is hardy through most of the UK and northern Europe. In colder and more exposed places the stems often freeze back to ground level, but the bush sends up new shoots from the base once the soil warms. Since it flowers on new wood anyway, that dieback is rarely a problem, and in practice it does the same job as the spring pruning. Cover the root collar with leaves or bark mulch for the first few winters, and hold off writing the shrub off until June. New shoots can be slow.
Varieties, height and flower colour
The heights in the table apply after annual spring pruning. Left unpruned the large varieties grow taller but thinner.
| Variety or variety group | Flower colour | Height | Worth knowing |
|---|---|---|---|
| Large varieties, for example 'Black Knight' | Deep violet to almost blackish purple | 180-240 cm | The most panicles, but also the most seed to cut away |
| 'Nanho Purple' | Lavender purple | 90-150 cm | Narrow leaves and a denser habit |
| 'White Profusion' | White | 150-180 cm | Holds the RHS Award of Garden Merit since 1993, hardiness rating H6 |
| Lo & Behold group, for example 'Blue Chip' | Blue, purple, pink and ruby red | 60-90 cm | Sold as sterile or nearly seedless |
| 'Miss Molly' | Magenta red | 120-150 cm | Sold as sterile or nearly seedless |
For a container, pick a low growing variety from the table. The Lo & Behold group at 60 to 90 cm is the safest, and 'Nanho Purple' at 90 to 150 cm works if the pot stands steady. The pot needs to hold at least 40 litres and to stand cool and frost free over winter.
The seeding you should know about
A single panicle can hold up to 40,000 seeds. The seeds are small and winged, travel far on wind and water and stay viable in the soil for 3-5 years. Germination is high. That is why the species has been on the EPPO list of invasive alien plants in Europe since 2006, and why it is regulated in Spain and Switzerland among others. In the American states of Oregon and Washington it is classed as a weed.
In the UK the shrub is thoroughly naturalised on railway embankments, walls and brownfield ground, but it is not listed in Part II of Schedule 9 to the Wildlife and Countryside Act 1981, so growing it in your garden is not restricted. What the Act covers is the wild. In England and Wales, section 14 makes it an offence to plant or otherwise cause to grow in the wild a plant listed in Schedule 9, and butterfly bush is not on that list. In Scotland the wording is wider: it is an offence to plant, or otherwise cause to grow, any plant in the wild at a place outwith its native range, and that does cover butterfly bush. So keep prunings and self sown seedlings off waste ground and out of the hedgerow. Either way, cut the faded panicles off before they dry and split open, ideally once a week from mid August. It lengthens the flowering and often gives a second flush of smaller panicles, while the seed never reaches the surroundings.
If you want to sidestep the question altogether, there are variety groups sold as sterile or nearly seedless. Oregon eased its ban in 2009 and has since allowed approved varieties and documented hybrids, and the threshold usually quoted in that context sits at around two per cent viable seed. Take the figure as an order of magnitude. A variety sold as sterile can still set the odd viable seed, so deadhead that one too. If you live near a watercourse, a railway embankment or a gravel pit, such a variety is a sensible choice anyway, because disturbed, free draining ground of exactly that kind is what the species colonises first.
Nectar for the butterflies, but no food for the caterpillars
Butterfly bush is a nectar plant for adult butterflies. The caterpillars do not eat it. Small tortoiseshell, peacock, red admiral and comma all lay their eggs on stinging nettle, and without host plants you get visitors but no new generation of butterflies in the garden. A patch of nettles of at least one square metre in a sunny spot goes a long way.
The painted lady is not one of the nettle feeders, even though it often gets counted in the same list. Its caterpillars live on thistles, burdock and other daisy family plants. If you want to keep it through the summer, leave a thistle or two standing in a sunny corner. How the different pieces fit together is set out in our article on how to make a butterfly garden.
Butterfly bush flowers from July, which leaves spring and early summer without nectar. Fill that gap with annual nectar plants from our range of seeds for pollinators. Purpletop vervain (Verbena bonariensis) is a good neighbour because it flowers at the same time and keeps going until the frosts, and purpletop vervain seed is sown in March. More options sit among our flower seeds.
Every butterfly is welcome in the border. The kitchen garden is another matter. The caterpillars of the cabbage white eat kale, broccoli and cauliflower, and there insect netting is the answer rather than more flowers.
Five mistakes that cost you flowers
Pruning in autumn: the cut surfaces die back and the shrub goes into winter with open wounds. Wait until April.
Skipping the pruning: after two unpruned years the shrub is bare at the base and the panicles are noticeably shorter.
Cutting too timidly: taking only 20 cm off the top gives many weak shoots. Go down to 30-50 cm.
Planting somewhere too wet: root rot in cold, waterlogged soil kills more shrubs than frost does.
Leaving the panicles to dry on the plant: every panicle left standing is tens of thousands of seeds on their way into the surroundings.
Author: Emma Vogiatzi
Fact-checked by Erik Hoekstra
Last updated 2026-09-01