Smooth aster

Smooth aster: how do you recognise it?

Habit

Sturdy, upright clump 0.8–1.2 m tall and about 50 cm wide, with heavily branched stems at the top.

Foliage

Lance-shaped, blue-green, smooth and slightly leathery; the leaves half clasp the stem.

Flower

Loose sprays of daisy-like flowers 2–3 cm across in violet-blue with a yellow centre, in September and October.

Roots

Short rhizomes that slowly widen the clump; easy to divide.

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

Why grow it?

• Flowers in September and October, when many other perennials have finished.
• The smooth, blue-green foliage is a handsome backdrop all summer and not very prone to powdery mildew.
• Tolerates drier soil than most asters, without needing much care.
• Bees and butterflies find nectar here late in the season.
• Good for cutting and sturdy enough to stand without support in most gardens.

Smooth aster: where does it grow best?

• Full sun: it stays sturdy and flowers best.
• Ordinary garden soil: sand or loam, acid to chalky. A moderately fertile soil is ideal.
• Reasonably moist to fairly dry; it tolerates drought better than most asters. It does not need wet soil.
• Allow about 50 cm between plants.

Light

Sun

Soil type

Sand or loam

Acidity

Not fussy

Moisture

Dry or normal

Size

1 m tall, 0.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Stonecrop: Pink to red flower heads in the same autumn period and the same sunny spot.
• Feather reed grass: An upright ornamental grass that supports the loose flower sprays.
• Black-eyed Susan: Yellow flowers make a lovely contrast with the violet-blue.
• Coneflower: Keeps flowering into late summer in the same sun.

Smooth aster: when and how to plant it?

Plant in March–May and September–October.

1. Plant in March–May or in September–October, when the soil is not frozen.
2. Dig a hole twice as wide as the root ball and mix in a little compost.
3. Set the plant at the same depth as in its pot, with the top of the root ball level with the soil.
4. Leave 50 cm between plants.
5. Water thoroughly straight away and keep the soil lightly moist in the first season.
6. Spread a thin layer of compost or leaf mould around the plant.

Care

Water

In the first year water weekly in dry weather. After that it tolerates drought well; water only in long dry spells.

Feeding

A thin layer of compost in spring. Over-rich soil gives long, floppy stems.

Support

Usually not needed in full sun. In rich soil or a windy spot, a ring of twigs helps.

Spent flowers

Leave them: the seedheads and stems give structure in winter and insects overwinter in them.

Dividing

Dividing the clump every 3–4 years in spring keeps the plant vigorous and flowering well.

Tip: Plant it in full sun in moderately fertile soil: it stays sturdy and rarely needs support. Leave the stems standing in winter for insects.

Smooth aster: when to prune it?

Pruning months: March.

When: In March, before the new shoots come through.

How:

• Cut all the old stems back to about 10 cm above the ground.
• Use sharp secateurs or shears and clear away the clippings.
• During the season, remove dead or broken stems at the base.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April: cut the clump with a spade into pieces with roots and shoots and replant at once.

Cuttings

In April–May: take 8–10 cm cuttings from the young shoots at the base and root them in moist cutting compost. They root in a few weeks.

Seed

Sow outdoors in spring in a seedbed. Seedlings may differ from the parent plant.

Smooth aster: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, down to about −30 °C: no protection is needed in Belgium.
• Leave the spent stems standing until March: they decorate the winter garden and shelter insects.
• In a pot: put it against a wall and wrap the pot in hessian in severe frost.

Diseases and pests

• Powdery mildew: White powder on the leaves, mostly in dry weather and when plants are too close together. This aster is not very prone to it; give space and water at the base.
• Slugs: They eat young shoots in spring. Collect them in the evening and protect young plants.
• Aphids: On young shoots in summer. Spray off with water; ladybirds help.
• Flopping stems: On over-rich soil or in shade. Plant in full sun and mix less compost into the soil.

Through the year

• March: Cut back to 10 cm. Add compost. Plant or divide.
• April: Plant or divide. Take cuttings from young shoots.
• May: Plant. Watch for slugs.
• June: In the first year, water in dry weather.
• July: Growth. In the first year, water in dry weather.
• August: Buds form.
• September: Flowering begins. Planting is still possible.
• October: Full flower. Planting or dividing is still possible.
• November: Leave the stems as winter decoration and for insects.
• December: Dormant.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The name aster comes from the Greek for ‘star’, after the shape of the flower.
• North American asters were moved to the genus Symphyotrichum in the 1990s, so they sometimes appear under two names in catalogues.
• The name smooth aster refers to the smooth, hairless leaves.