Symphyotrichum cordifolium

RHS Plant Profile

blue wood aster

Synonyms

Aster sagittifolius Wed.
Aster cordifolius

Herbaceous Perennial

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A clump-forming perennial, up to 1.5m high, with upright, branching stems and oval to heart-shaped green leaves. Clusters of small daisy-like flowers, in pale violet, blue or occasionally white, are produced from late summer well into autumn

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam, Sand

Max Height

1-1.5 metres

Max Spread

0.5-1 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.5-1 metres
Max Height: 1-1.5 metres

Growing Conditions

Chalk Clay Loam Sand

Moisture: Moist but well–drained
pH: Acid or Alkaline or Neutral

Position

Full sun Partial shade

Aspect: East–facing or South–facing or West–facing
Exposure: Exposed or Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

H1A: under glass all year (>15C)
H1B: can be grown outside in the summer (10 - 15)
H1C: can be grown outside in the summer (5 - 10)
H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
H4: hardy through most of the UK (-10 to -5)
H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
H6: hardy in all of UK and northern Europe (-20 to -15)
H7: hardy in the severest European continental climates (< -20): H7

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Asteraceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Clump forming
Genus: Symphyotrichum includes around 90 species of annuals, biennials and perennials, mostly spread through the Americas, that were formerly included within the genus Aster. Leaves are simple, lance-shaped and entire, but it is their daisy-like flowerheads that they are grown for; central disc florets are typically yellow, surrounded by strap-shaped ray florets in shades of pink, blue, purple or white
Name Status: Correct
Plant Range: USA

How to Grow

Cultivation

Grow in fertile, moisture-retentive soil, in sun or part shade; add mulch after cutting back in autumn. Plants may need support, see staking perennials. Divide every third year to retain vigour and flower quality. See aster cultivation

Propagation

Propagate by seed or by division in spring, replanting only vigorous young shoots

Suggested planting locations and garden types

Cottage and informal garden
Prairie planting
Wildlife gardens
Coastal
Flower borders and beds
Cut flowers

Pruning

Cut stems close to the ground in late autumn

Pests

May be susceptible to leaf and bud eelworm, aphids, slugs and snails

Diseases

May be susceptible to Fusarium wilt, powdery mildews, leaf spots and grey moulds