Aspen

Aspen: how do you recognise it?

Habit

Tree of 10–20 m with a narrow, open crown about 8 m across; often forms a group through its suckers.

Leaves

Alternate, almost round, 3–7 cm, with coarse, wavy teeth. Long, sideways-flattened leaf stalk.

Bark

Smooth, grey-green with diamond-shaped lenticels; darker at the base.

Flowers

Grey, hairy catkins in March.

Fruit

Fluffy seeds in May.

Difference from hybrid black poplar

Hybrid black poplar has a triangular leaf with a finely toothed edge and grows much bigger.

Flowering: March · Pruning: November–March

Looks like it, but isn’t

• Hybrid black poplar Populus × canadensis: triangular leaf with a finely toothed edge. Difference from hybrid black poplar

Why grow it?

• The sound of the trembling leaves, even on an almost still day.
• Lovely yellow to orange-red autumn colour.
• Important for many insects; woodpeckers excavate their nests in old trunks.
• A pioneer that also grows on poor, dry or wet soil.
• A narrow, light crown that casts little shade.

Aspen: where does it grow best?

• Full sun: in shade it languishes.
• Almost any soil, from poor sand to wet clay, dry or moist.
• Choose a spot where suckers can do no harm: a wildlife garden, a woodland edge, a meadow or a lawn that you mow.
• Keep it away from the house, patio, drains and sewers: the roots travel far and seek out water.

Light

Full sun

Legal basis

Any garden soil

Moisture

Dry to wet

Size

20 m tall, 8 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Silver birch: Another pioneer of poor soil: white next to grey-green, and both with yellow autumn colour.
• Rowan: A small native tree with orange-red berries for the woodland edge.
• Alder buckthorn: A native shrub for the woodland edge, food plant of the brimstone butterfly and popular with bees.

Good and bad companions

Goes well with

• Tolerate the shade under this tree: oregon grape, rhododendron, oleaster, japanese skimmia, garden privet, camellia, laurustinus, box-leaved honeysuckle

Aspen: when and how to plant it?

1. Plant from November to March when the ground isn’t frozen.
2. Young whips (forestry transplants) establish best; plant them in a group of three or five if you like.
3. Plant it in or next to a lawn or meadow, so that you can mow off the suckers.
4. Water after planting and during dry spells in the first year.

Care

Suckers

Mow or cut off root suckers regularly where you don’t want them.

Watering

Only in dry spells during the first year.

Feeding

Not needed.

Dead wood

Leave a dead or hollow trunk standing if it can’t fall on anyone: woodpeckers and insects will make good use of it.

Tip: Want the rustling without a lawn full of suckers? Plant a small group of aspens at the edge of a meadow or a lawn that you mow: the mower will keep the suckers short without any extra effort.

Aspen: when to prune it?

Pruning months: November–March.

When: Dead, diseased and broken branches can be removed at any time of year. If you do need to prune, do it during winter dormancy (November–March).

How:

• Needs little pruning: just remove dead, broken and crossing branches.
• Keep root suckers in check by mowing them off or cutting them low.

Caution: Don’t chop into the roots or fell the tree to get rid of the suckers: that only makes even more of them come up.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Root suckers

In winter, dig up a sucker together with a piece of the root it is attached to, and replant it straight away.

Sowing

The fluffy seeds germinate within days but only stay viable for a short time: sow them straight away in May on moist soil. With this poplar, stem cuttings root poorly.

Aspen: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Fully hardy.
• In winter the smooth, grey-green bark with diamond-shaped lenticels stands out.

Diseases and pests

• Suckers: Young trees popping up all over the lawn and border. Mow them off regularly; digging them out achieves little.
• Poplar rust: Orange spore pustules on the leaves in late summer; the leaves drop a little early. Harmless.
• Red poplar leaf beetle: A red beetle and its larvae eat the leaves of young trees and suckers. Usually harmless.

Through the year

• January: Prune if needed: remove dead and crossing branches.
• February: Pruning; planting season when there is no frost.
• March: Grey catkins; last month for pruning and planting.
• May: Fluffy seeds: sow straight away.
• June: Mow off suckers.
• August: Mow off suckers again; water young trees in dry spells.
• October: Yellow to orange-red autumn colour.
• November: Planting season; pruning can start again.
• December: Prune if necessary; dig up suckers with root to replant.

What can you use it for?

For wildlife

Important for many insects; old trunks are used by woodpeckers.

Wood

Light wood for matches and sauna benches.

Garden and landscape

Lovely yellow to orange-red autumn colour, and the rustling leaves sound wonderful.

Good for wildlife

Caterpillars

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

Birds

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

Did you know?

• The Latin name tremula means ‘trembling’: thanks to the flattened leaf stalk, the leaves are never still.
• A group of aspens is often a single plant: all the trunks are suckers from the same root system.
• The light wood is used for matches and sauna benches.
• According to an old Christian legend, the leaves of the aspen have trembled ever since the cross of Christ was made from its wood.
• A grove of aspens is often a single individual: through root suckers, all the trunks grow from the same root system.