Alder buckthorn

Alder buckthorn: how do you recognise it?

Habit

Airy, upright shrub or small tree of 2–5 m, often multi-stemmed and without thorns.

Leaf

Alternate, oval, 4–7 cm, untoothed and glossy; 7–9 pairs of parallel, curved veins.

Bark

Greyish-brown with white, streak-like lenticels; inner bark yellow.

Flower

Small greenish-white flowers from May to September.

Fruit

Berries, first green, then red, black when ripe; poisonous. Often all the colours hang on one twig at once.

Difference from common dogwood

Common dogwood has opposite leaves; in alder buckthorn they are alternate.

Flowering: May–August · Pruning: November–March

Identify by feature: Red berries · Black berries

Looks like it, but isn’t

• Common dogwood Cornus sanguinea: opposite leaves. Difference from common dogwood

Why grow it?

• Flowers from May into September: months of nectar for bees and bumblebees.
• Food plant of the brimstone butterfly: the caterpillars feed on the leaves.
• Berries for thrushes and blackbirds, in summer and autumn.
• Grows on wet, acid soil where few other shrubs thrive.
• Needs little pruning; can be coppiced.

Alder buckthorn: where does it grow best?

• Sun to partial shade; also tolerates the light shade of a woodland edge.
• Moist to wet, acid soil, such as sand or peat; not on chalk.
• Allow about 3 m in width.
• Ideal for a damp garden edge, a pond bank, a hedgerow or a mixed hedge on sandy soil.

Light

Sun or partial shade

Legal basis

Acid soil

Moisture

Moist to wet

Size

5 m tall, 3 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Alder: Together in a wet hedgerow or on a pond bank.
• Bog-myrtle: A fragrant native shrub for the same wet, acid soil.
• Rowan: Flowers in May and gives red berries for birds in autumn, even on acid sand.
• Holly: Evergreen: a winter shelter for the brimstone, right next to its food plant.

Good and bad companions

Goes well with

• Together a mixed native hedge, good for birds and insects: hawthorn, blackthorn, hazel, dog rose, common dogwood, guelder rose, wild privet, field maple

Alder buckthorn: when and how to plant it?

1. Plant from November to March, as young forestry stock (bare-root) or from a pot.
2. In a hedgerow or hedge: one plant every 1–1.5 m, mixed with other native shrubs of wet soil.
3. Plant at the same depth as before and firm the soil well.
4. Don’t add lime or fertiliser: it likes a poor, acid soil.

Care

Watering

In dry spells during the first year; after that only in long, dry summers on high, sandy ground.

Feeding

Not needed; simply leave fallen leaves under the shrub.

Caterpillars

Feeding by brimstone caterpillars is the whole point: the shrub recovers on its own.

Seedlings

Birds spread it; weed out seedlings where you don’t want them.

Tip: Want brimstone butterflies in the garden? Plant an alder buckthorn in a sunny, sheltered spot, with holly or ivy nearby for overwintering.

Alder buckthorn: when to prune it?

Pruning months: November–March.

When: In winter (November–March), and only when needed. Dead, diseased and broken branches can be removed at any time of year.

How:

• Needs little pruning: keep its airy, natural shape.
• Now and then, remove an old or leaning stem at the base.
• If the shrub gets too big or bare, coppice it to 20–30 cm above the ground; it soon regrows.

Caution: Prune preferably before mid-March: after that, birds nest in the shrub and brimstones lay their eggs on the young leaves.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Sowing

Take the seeds from ripe, black berries and sow them outdoors in autumn; they need a cold winter and germinate in spring. Wash your hands afterwards.

Layering

Bend a low, supple branch to the ground, cover it with soil and cut it free after a year.

Alder buckthorn: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Fully hardy.
• In winter you can recognise it by the dark twigs with white streaks and by the hairy buds without bud scales.
• Brimstones overwinter as adult butterflies among evergreen leaves, such as ivy and holly: plant some nearby.

Diseases and pests

• Brimstone caterpillars: Holes in the leaves in May–June. No problem: leave them, they will become brimstone butterflies.
• Drought: Limp, withering leaves on dry, high ground. Water, mulch, or choose a damper spot.
• Chalky soil: Yellow leaves and weak growth. Alder buckthorn belongs on acid soil; on chalk, buckthorn is a better choice, and it is also a brimstone food plant.

Through the year

• January: Prune only if needed; remove dead wood.
• February: Prune or coppice, if needed.
• March: Last pruning and planting, before mid-March.
• April: Brimstones lay eggs on the young leaves.
• May: Flowering starts; brimstone caterpillars.
• July: Flowers and green, red and black berries all at once.
• September: Last flowers; birds eat the black berries.
• November: Planting; pruning is possible again.
• December: Winter pruning if needed.

What can you use it for?

For wildlife

Food plant of the brimstone butterfly; flowers for months for bees.

Garden and landscape

Native shrub for a damp, acid spot.

Caution: The berries are poisonous.

Good for wildlife

Caterpillars

Host plant: caterpillars of butterflies or moths eat the leaves.

Bees

Nectar and pollen for honeybees and wild bees.

Bumblebees

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

Birds

Berries, seeds or insects as food, or a place to nest.

Hoverflies

Open flowers for hoverflies; many of their larvae eat aphids.

Did you know?

• Its charcoal was once used to make gunpowder; food plant of the brimstone butterfly.
• Another name is glossy buckthorn. The dried, aged bark was once used as a laxative; fresh bark is too strong and poisonous.
• Because it flowers for months, the shrub carries flowers and green, red and black berries at the same time.
• Frangula comes from the Latin frangere, to break, after its brittle twigs; alnus refers to the leaves, which resemble those of alder.
• The dried bark was once a well-known laxative, sold in pharmacies.