White wood aster

White wood aster: how do you recognise it?

Habit

A loose, slightly arching clump 40–60 cm tall and about as wide, which slowly spreads.

Stems

Thin, dark purple to almost black, with zigzag branching in the flower head.

Leaves

Heart-shaped, coarsely toothed and stalked, dark green; up to about 15 cm at the base, smaller higher up.

Flowers

White stars 2–2.5 cm across in loose sprays, from August to October; the yellow centre later turns reddish purple.

Roots

Shallow, creeping rhizomes.

Flowering: August–October · Plants: March–May and September–October · Pruning: March and June

Why grow it?

• Late flowers from August to October, when the shade border has usually finished.
• One of the few asters for dry shade under trees.
• Elegant, almost black, zigzagging stems that make the white cloud of flowers stand out even more.
• A late source of nectar and pollen for bees, hoverflies and butterflies.
• It spreads gently into a loose ground cover among ferns and grasses.

White wood aster: where does it grow best?

• Partial or full shade: under deciduous trees, along a hedge or on the north side of the house.
• Sand, loam or clay, acid, neutral or chalky; preferably with some humus.
• Dry to normal soil; once established it copes well with drought under trees.
• In deep, dark shade it flowers less; light shade is ideal.
• Plant 40–50 cm apart, in groups of three to five, for a loose ground cover.

Light

Partial shade and shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

0.6 m tall, 0.6 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Ferns: Their fine fronds make a fresh backdrop for the white stars.
• Greater woodrush: An evergreen grass for the same dry shade under trees.
• Elephant’s ears: Large, glossy leaves as a calm base for the aster to lean over.
• Hosta: Broad leaves that frame the looser wood aster nicely.
• Barrenwort: A low, tough ground cover for the same dry shade.

White wood aster: when and how to plant it?

Plant in March–May and September–October.

1. Plant in March–May or September–October.
2. Loosen the soil and mix in some compost or leaf mould, especially under trees.
3. Dig a hole twice as wide as the root ball and set the plant at the same depth as it was in its pot.
4. Space plants 40–50 cm apart.
5. Water in well straight away and keep the soil moist during the first summer.
6. Mulch with leaf mould.

Care

Watering

In dry weather during the first year. After that only in very dry summers, as soil under trees dries out quickly.

Feeding

A layer of compost or leaf mould in March; nothing more is needed.

Support

It leans a little, and that is how it should be. For a more upright plant, cut it back by a third in early June or let it lean on its neighbours.

Mulching

Leave fallen leaves in place or add leaf mould.

Spent flowers

Leave them: the fluffy seed heads and dark stems decorate the winter garden.

Tip: Plant it in a group of three to five under trees and let it roam freely among ferns and grasses: in late summer it forms a white cloud in the shade.

White wood aster: when to prune it?

Pruning months: March and June.

When: Cut the old stems down in March, before the new shoots appear. Optionally, a light trim in early June.

How:

• Leave the stems standing in winter: they look good and insects overwinter in them.
• In March, cut all the old stems down to just above the ground.
• For a more compact plant that flops less, cut the stems back by a third in early June; it will then flower slightly later.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April, cut off a piece with rhizome and shoots from the edge and replant it elsewhere. The easiest method.

Cuttings

In April–May, take 5–8 cm cuttings from young shoots and insert them in moist cutting compost.

Seed

Sow in autumn in a pot outdoors: the seed needs a cold spell. Seedlings often flower only in their second year.

White wood aster: how does it get through the winter?

Hardy to −35 °C.

• Extremely hardy, to about −35 °C: in Belgium it needs no protection.
• The top growth dies back; leave the stems standing until March.
• In a pot it also overwinters outdoors, as long as water can drain away.

Diseases and pests

• Powdery mildew: White powder on the leaves, especially in dry weather in late summer. Water in dry spells and leave some space; it usually suffers less than many garden asters.
• Slugs: They eat the young shoots in spring. Pick them off in the evening or lay down a board for them to gather under.
• Flopping: In rich soil or deep shade the stems fall apart. Cut back in early June and feed less.
• Few flowers: Shade that is too dense. Move it to light shade, for example under a tree with an open canopy.

Through the year

• March: Cut down old stems. Plant or divide. Add compost.
• April: Plant. Watch for slugs on the young shoots.
• May: Plant. Take cuttings.
• June: In early June, cut back by a third if you wish.
• July: Water in dry weather.
• August: Flowering begins. Bees and butterflies on the flowers.
• September: Full flower. Plant.
• October: Last flowers. Plant.
• December: Leave the dark stems and seed heads standing.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Divaricata means ‘widely spreading’ and refers to the broadly spreading, zigzag branching of the flower head.
• Botanists have split the American asters into other genera, such as Eurybia and Symphyotrichum; that is why it is no longer called Aster divaricatus.
• The British garden designer Gertrude Jekyll liked to combine it with bergenias.