Butterfly bush

Butterfly bush: how do you recognise it?

Habit

Shrub of 2–4 m with long, arching branches; regrows every year after hard pruning.

Leaf

Opposite, lance-shaped, 10–25 cm, finely toothed; white-felted underneath.

Bark

Brown and peeling.

Flower

Long panicles of fragrant purple (or white, pink) flowers, July–September.

Fruit

Small capsules full of dust-fine seeds; a single shrub produces many thousands, spread by the wind.

Difference from white willow

White willow has alternate leaves and catkins.

Flowering: July–September · Pruning: March–April

Identify by feature: Long, narrow leaves · White or silver underside · Purple or blue flowers

Looks like it, but isn’t

• White willow Salix alba: alternate leaves and catkins. Difference from white willow

Why grow it?

• Long, fragrant flower spikes from July to September, when many other shrubs have finished flowering.
• Attracts lots of butterflies and bees for nectar, though it doesn’t feed their caterpillars.
• Grows on dry, poor soil in full sun.

Butterfly bush: where does it grow best?

• Full sun; in shade it flowers poorly and becomes floppy.
• Any free-draining soil, even dry and poor; no wet feet in winter.
• Allow 3 m width.
• Not near nature reserves, verges or waste ground, where seedlings spring up easily.

Light

Full sun

Legal basis

Any garden soil

Moisture

Dry

Size

4 m tall, 3 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Wild privet: A native alternative: fragrant white flowers in June–July full of butterflies, and the food plant of the privet hawk-moth.
• Alder buckthorn: A native shrub that flowers for a long time for bees; brimstone caterpillars feed on its leaves.
• Wild marjoram: A native perennial for the same dry, sunny spot, busy with butterflies.
• English lavender: Flowers in summer in the same sunny, dry spot, for butterflies and bees.

Good and bad companions

Best kept away from

• Do not plant under the dense crown of these trees: norway spruce, european silver fir, nordmann fir, douglas fir, yew, horse chestnut, norway maple, sycamore

Butterfly bush: when and how to plant it?

1. Consider a native alternative first: wild privet and alder buckthorn also attract butterflies, and feed caterpillars too (see companions).
2. Plant from a container in April–May, so it roots well before winter.
3. Loosen the soil and, on heavy soil, mix in some coarse sand or gravel.
4. Water in dry spells during the first year; after that it is rarely needed.

Care

Faded flower spikes

Cut off every faded spike to just above a pair of buds, throughout the season: this prevents seed and keeps it flowering longer.

Seedlings

Pull up seedlings in and around the garden straight away; when young they are still easy to remove.

Watering

In dry spells during the first year; not needed after that.

Feeding

Not needed; on rich soil it becomes floppy and flowers less.

Tip: If you already have a butterfly bush, put a weekly round with the secateurs in your diary from July to October: not a single spike should set seed. If you are planting something new for butterflies, choose a native shrub.

Butterfly bush: when to prune it?

Pruning months: March–April.

When: Late March–April.

How:

• Cut it back hard every spring to 30–50 cm: it flowers on new shoots.
• On an old shrub, also remove a few of the oldest, thickest stems at the base.
• In summer, cut off faded flower spikes before the seeds ripen.

Caution: Wait until late March for the spring pruning, so the new shoots don’t get frosted. Cut-off spikes with seed don’t belong on the compost heap.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

Summer and winter cuttings root easily. Better not to propagate it, though: there are already plenty of butterfly bushes running wild.

Butterfly bush: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Hardy; in severe winters the stems sometimes die back, but it regrows from the base.
• Leave the stems until the spring pruning, but cut off all old flower spikes before winter.

Diseases and pests

• Running wild: The seeds germinate in every crack: in walls, on roofs, along railway lines and on waste ground, where butterfly bush crowds out native plants. Cut off faded spikes and pull up seedlings.
• No food for caterpillars: Butterflies come for the nectar, but their caterpillars live on native plants such as nettles, alder buckthorn and buckthorn. Without those plants you are only helping butterflies halfway.
• Red spider mite and aphids: In hot, dry summers, sometimes spider mites (fine webbing, mottled leaves) or aphids. Hose down the leaves and water in dry spells.
• Tall, bare shrub: Without annual pruning it grows tall and bare, with small flower spikes high up. Prune hard every spring.

Through the year

• March: Late March: cut back hard to 30–50 cm.
• April: Last pruning month; plant from containers.
• July: Flowering begins: cut off faded spikes every week.
• August: Full bloom, full of butterflies; keep cutting off faded spikes.
• September: Last flowers; pull up seedlings nearby.
• October: Cut off all old flower spikes before the seeds blow away.

What can you use it for?

Garden and landscape

Summer-flowering shrub for sunny, dry spots.

For wildlife

Attracts lots of butterflies, though it doesn’t feed their caterpillars.

Caution: Spreads easily into the wild; cut off faded flower heads and don’t plant it near nature reserves.

Good for wildlife

Butterflies

Nectar for butterflies.

Moths

Nectar for moths, often from flowers that are scented in the evening.

Bumblebees

Nectar and pollen for bumblebees, also from deep flowers and early in spring.

Did you know?

• Runs wild along railway lines and on waste ground; cut off spent flower spikes to limit self-seeding.
• The name honours the English botanist Adam Buddle; ‘davidii’ refers to the French missionary and naturalist Armand David.
• It needs so little that you see it growing in walls, on roofs and in gutters.
• Buddleja honours the English clergyman and botanist Adam Buddle; davidii the French missionary Armand David, who first recorded the shrub in China.
• After the Second World War it sprang up in huge numbers on the bomb sites of cities such as London: it thrives on rubble and old walls.