Green alder

How to recognise it

Habit

Broad, multi-stemmed shrub of 1–3 m, sometimes up to 5 m in the wild, with flexible stems that often arch upwards. Bark smooth, grey to grey-brown.

Leaves

Alternate, oval to elliptical, 3–8 cm, with a pointed tip and a fine, sharply double-toothed edge; fresh green and slightly sticky when young. No notched tip as in common alder.

Buds

Stalkless, pointed, shiny and slightly sticky. In common and grey alder the buds are stalked.

Flowers

Monoecious. The long yellow male catkins form in summer and spend the winter naked on the twigs; they open in April–May. The female catkins overwinter inside the buds and only appear together with the leaves. Wind-pollinated.

Fruit/Seed

Small, egg-shaped cones of 1–1.5 cm on long stalks, green at first, later brown and woody. The nutlets have a broad, papery wing.

Confusion with

Common alder: a tree with round leaves with a notched tip, stalked buds and flowers in February–March, before the leaves. Grey alder: a tree with grey, hairy leaf undersides and stalked buds. Hazel: round, softly hairy leaves and hazelnuts instead of cones.

Flowering: April–May · Pruning: December–February

Why grow it?

• With the help of root nodules it fixes nitrogen from the air, so it grows well even on poor, bare ground.
• A tough shrub for cool, damp spots and slopes: its roots hold the soil together.
• As with other alders, the seeds in its small cones are winter food for siskins and redpolls.
• Like other alders it feeds the caterpillars of various moths and other insects.
• Stays much smaller than common alder and grey alder, so it also fits in an ordinary garden.
• An unusual mountain plant for anyone who wants a piece of the Alps in the garden, for example at the edge of a pond.

Green alder: where does it grow best?

• In the wild: avalanche tracks, steep damp slopes, the banks of mountain streams and clearings around the tree line, mostly on lime-poor soil.
• Sun to half shade, in a cool spot; in a hot, dry place it suffers.
• Moist to wet, preferably acid to neutral soil: loam, sand or gravel. Poor is fine, dry is not.
• In the garden: at the edge of a pond, on a north-facing slope or in a damp border; as a single shrub or in a group on a bank you want to stabilise.

Goes well with

• Rowan: Often grows with green alder in the mountains; white flowers and orange-red berries for birds.
• Goat’s beard: Tall creamy white plumes in June, in the same cool, damp spot.
• Lady fern: Fine, fresh green fronds for the base, in half shade.
• Meadowsweet: Fragrant creamy white plumes in summer, on wet soil.

Green alder: when and how to plant it?

1. Buy a plant from a nursery for native or unusual shrubs; it is not sold everywhere. Never take plants or seedlings from the wild, not even in the mountains on holiday.
2. Plant while dormant, from November to March, when the ground is not frozen.
3. Dig a hole twice as wide as the root ball and do not add any fertiliser.
4. Set the plant at the same depth as in the pot, firm the soil well and water thoroughly straight away.
5. Allow 1.5–2 m between plants for a group or an informal hedge.
6. Keep the soil moist in the first year and spread a layer of leaf mould around the base.

Care

Water

It must never dry out for long. In the first year water weekly in dry weather; after that only in long, dry summers.

Feeding

Not needed: it makes its own nitrogen with its root nodules.

Mulching

A layer of leaf mould or wood chips keeps the soil cool and moist.

Soil

It grows best on acid to neutral soil; on very chalky soil it does less well.

Space

It forms a dense thicket. Removing a few old stems every few years keeps it open and within bounds.

Tip: Plant it in the coolest, dampest spot in your garden, for example on the north side of a pond: this mountain shrub feels at home there and keeps its leaves fresh until autumn.

Pruning and mowing

Pruning months: December–February.

When: In winter, from December to February, outside the nesting season.

How:

• Little needed: remove dead and broken branches and thin out a dense shrub by sawing off a few old stems at the base.
• If it gets too big, coppice it completely every 5–10 years to 10–20 cm above the ground; it regrows vigorously.
• Coppice in stages, a few stems at a time, so there is always cover for birds.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Pick the cones in October–November, let them dry until they open and sow the seeds in autumn in a pot outdoors, on the surface of moist compost. Winter cold improves germination.

Layering

In spring, bend a low branch into the soil and pin it down; after a year it has roots and you can cut it free. In the mountains this happens by itself under the snow.

Green alder: how does it get through the winter?

Hardy to −40 °C.

• Deciduous: in autumn the leaves often drop while still green or yellowish green.
• Extremely hardy, to −40 °C and colder; in the mountains it spends the winter under a thick blanket of snow.
• The naked male catkins and small brown cones hang on the twigs all winter.
• In winter siskins and other finches pick the seeds out of the cones.

Diseases and pests

• Alder leaf beetle: Small steel-blue beetles and their black larvae eat holes in the leaves in summer. A healthy shrub recovers; birds and predatory insects eat them.
• Drought and heat: Brown leaf edges and early leaf fall in a hot, dry spot. Water and mulch, or move it to a cooler place.
• Aphids: On young shoots in spring. Ladybirds and birds usually clear them up; otherwise spray them off with water.
• Overly dense thicket: Without pruning it becomes wide and dense. Sawing out old stems in stages keeps it young and compact.

Through the year

• January: Dormant. Prune or coppice in mild weather. Planting.
• February: Last pruning. Planting.
• March: Planting. The male catkins swell.
• April: Leaves unfold and the male catkins open: flowering begins.
• May: Flowering; the female catkins appear together with the leaves. Layering.
• June: Water in dry weather. Watch for alder leaf beetle.
• July: Keep the soil moist and mulch.
• September: The cones turn brown.
• October: Leaf fall. Pick cones for seed.
• November: Planting. Sow in a pot outdoors.
• December: Dormant. Prune or coppice.

Did you know?

• The name alnobetula literally means ‘alder-birch’: the species was first described as a birch.
• Its flexible stems are pressed flat by snow and avalanches and then straighten up again; that is how it survives on avalanche tracks where trees snap.
• In the Alps it is spreading into abandoned mountain pastures: its dense thickets crowd out flower-rich grassland and enrich the soil with nitrogen.