Butterfly bush: when and how to prune

Butterfly bush: when to prune it?

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Wait until late March or April for the spring prune, when the hard frosts are over: prune earlier and the young shoots may be caught by frost.

From July until the last flowers, cut off the faded spikes every week, just above a pair of buds: that way it sets no seed and keeps flowering for longer.

In October, cut off any old flower spikes still left, before the seeds blow away; leave the stems themselves until spring.

What else to prune in those months? March · April

Butterfly bush: how to prune it?

1. In spring, cut all stems back to 30–50 cm above the ground, just above a pair of healthy buds or young shoots.
2. On an old shrub, also saw one or two of the oldest, thickest stems off at the base, so young stems can take their place.
3. Remove dead and thin stems. The wood isn’t hard: good secateurs or loppers are usually enough.
4. In summer, cut faded spikes back to just above the first pair of buds or side shoots: new, smaller spikes grow from there.
5. Faded spikes with seed don’t belong on the compost heap: put them in the general waste. Pull up seedlings in and around the garden straight away, while they are still small.

How much to cut, and how often?

• Firmly every spring: the shrub grows back one and a half to two metres in a single season. Without pruning it becomes tall and bare, with small spikes at the top.
• Removing faded flower spikes is a job for the whole summer: once a week is enough.
• An old shrub with thick, gnarled stems can also be cut down to 30 cm: it regrows from the base. Saw off any stem that no longer shoots at the base.

What does it mean for wildlife?

• From July to September the spikes are full of nectar: peacocks, red admirals, small tortoiseshells and brimstones visit them, as do bumblebees and other bees.
• But the butterfly bush feeds no caterpillars: they live on native plants such as stinging nettle, alder buckthorn and purging buckthorn. To really help butterflies, plant those alongside it, or instead of it.
• Its dust-fine seeds blow a long way: the butterfly bush runs wild along railway lines, on waste ground and in walls, where it crowds out native plants. Don’t plant it near nature reserves, and for a new shrub choose a native species such as wild privet or alder buckthorn instead.
• The spring prune falls in the nesting season (15 March–15 August): check first that no bird is nesting in the shrub, as disturbing an active nest is against the law. Healthy prunings without flower spikes can go on a dead hedge.

Common mistakes

• Leaving the faded spikes on the shrub, so it seeds itself around the neighbourhood.
• Putting spikes with seed on the compost heap.
• Pruning too early, in February, after which the young shoots are killed by frost.
• Not pruning at all, so the shrub becomes tall and bare, with small flower spikes.
• Thinking a butterfly bush is enough for butterflies, when their caterpillars need native plants.

Nearby: related pruning guides

• Fountain butterfly bush (Buddleja alternifolia)
• Panicled hydrangea
• Lavender
• Wild privet
• Alder buckthorn

Similar to: Difference from Californian lilac · Difference from white willow

Plant profile: Butterfly bush · Pruning calendar and basic rules