River birch

River birch: how do you recognise it?

Habit

Broad, light, spreading crown, often with several stems; about 15 m tall and 10 m wide.

Bark

Salmon-pink to cinnamon-brown, peeling in large papery curls; darker and furrowed on old trunks.

Leaves

Diamond-shaped to oval, 5–8 cm, doubly toothed; dark green, yellow in autumn.

Flowers

Male catkins in April, small female catkins; no showy flower.

Fruit

Small fruiting catkins with winged seeds, which ripen early in summer.

Flowering: April · Plants: March–April and October–December · Pruning: August

Why grow it?

• Striking pink-brown bark that peels in curls and decorates the garden all winter.
• One of the few birches that tolerate heavy, wet soil and temporary flooding.
• Copes with heat better than other birches and is less prone to many birch pests.
• Multi-stemmed, it makes a superb specimen tree or a tree for the edge of a pond or stream.
• Yellow autumn colour and a light canopy, leaving room for underplanting.

River birch: where does it grow best?

• Sun or partial shade; it grows and colours best in a bright spot.
• Moist to wet soil: sand, loam, clay or peat, acid to neutral. On chalky soil the leaves may turn yellow.
• Normal to wet soil; also suitable for a pond edge, a swale or a hollow that sometimes floods.
• Allow for a crown 10 m wide and plant at least 6–8 m from buildings, drains and pipes.

Light

Sun and partial shade

Soil type

Sand, loam, clay or peat

Acidity

Acid or neutral

Moisture

Normal or wet

Size

15 m tall, 10 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Dogwood: Red or yellow stems make a lovely contrast with the pale bark.
• Bulrush: A natural companion at the edge of a pond.
• Yellow flag iris: Likes the same wet soil and flowers yellow in May–June.
• Rhododendron: Likes the same acid, moist soil under the light canopy.
• Ferns: A fresh, shady underplanting.

River birch: when and how to plant it?

Plant in March–April and October–December.

1. Plant in March–April or from October to December, when the soil is not frozen.
2. Dig a hole twice as wide as the root ball and just as deep.
3. Set the tree at the same depth as in its pot or at the nursery and backfill with the soil you dug out; do not add lime.
4. Add a stake and tie the trunk or trunks loosely with a tree tie.
5. Water generously straight away and spread 5–8 cm of wood chips or leaf mould around the base, keeping it clear of the trunk.

Care

Water

In the first two summers, water thoroughly every week in dry spells. A mature tree also tolerates wet soil, but extra water in prolonged drought is welcome.

Feeding

Usually unnecessary. On poor soil, apply a layer of compost under the canopy in spring.

Mulching

A layer of leaf mould or wood chips keeps the soil cool and moist and helps keep it acidic.

Staking

Tie a young tree to a stake for 2–3 years and check the tie every year.

Tidying

Leave the leaves as mulch, or rake them up if the tree overhangs a pond.

Tip: Plant it on wet or heavy soil where other trees struggle, but not on chalky soil, where the leaves turn yellow. Choose a multi-stemmed form for the best bark.

River birch: when to prune it?

Pruning months: August.

When: Prune as little as possible; if needed, in August, when the leaves are fully grown.

How:

• Remove dead, damaged and crossing branches.
• Cut small branches just outside the branch collar, never flush with the trunk.
• On a multi-stemmed tree, keep 3–5 strong, well-spaced stems and remove other protruding wood.
• Never remove more than a fifth of the crown in one year.

Caution: Do not prune in spring, when the sap is rising: birches bleed heavily then.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

The seed ripens as early as May–June and germinates easily. Sow it fresh in a tray of light, moist soil and keep the seedlings moist.

Buying

Cultivars such as ‘Heritage’ are propagated vegetatively; seed gives variation. For a specific cultivar, buy a nursery-grown young tree.

River birch: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in Belgium.
• In winter the peeling bark looks its best: place it in plain view, against a dark background.
• In a hard winter, give young trees an extra layer of mulch around the base.

Diseases and pests

• Yellow leaves with green veins: Iron deficiency (chlorosis) on chalky soil. Mulch with acidic leaf mould and, if needed, find a spot with more acidic soil.
• Early leaf drop in summer: In prolonged drought it sheds yellow leaves. Water generously in dry weather and apply a mulch.
• Aphids: Sticky leaves and sooty mould in summer. Ladybirds and tits usually deal with them.
• Birch rust: Small orange dots under the leaves in wet summers. Usually harmless; rake up fallen leaves.

Through the year

• January: Rest. Check the ties on young trees.
• March: Planting still possible. Refresh the mulch.
• April: Catkins open. Water young trees in dry weather.
• May: Seed begins to ripen. Check the mulch.
• June: Seed ripens and falls. Water in dry weather.
• August: Prune if needed. Remove dead branches.
• October: Yellow autumn colour. Planting can begin again.
• November: Plant. Leave the leaves or turn them into leaf mould.
• December: Plant while the soil is not frozen.

Did you know?

• River birch is the most heat-tolerant birch of North America.
• Its seed ripens in spring or early summer, whereas other birches shed seed in late summer or autumn.
• The Latin species name nigra refers to the dark, almost black bark of old trunks.