Centaurea jacea

RHS Plant Profile

brown knapweed

Synonyms

Centaurea amara
Centaurea viretorum

Herbaceous Perennial

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A vigorous herbaceous perennial, up to 1.5m high, with lance-shaped green leaves. Leaves and stems covered with fine white felting. Flowers in summer, producing buds encased in overlapping, light brown bracts edged with long white hairs, which open to showy mauve pink or lilac flowers, with a ring of long, narrow outer florets surrounding masses of tiny flowers in the centre

Position

Full sun

Soil Types

Chalk, 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 Loam Sand

Moisture: Well–drained
pH: Acid or Alkaline or Neutral

Position

Full sun

Aspect: 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): H6
Drought Resistance: Yes

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: Centaurea may be annuals, perennials or subshrubs, with simple or pinnately lobed leaves and showy thistle-like flowers-heads, often with enlarged outer florets
Name Status: Correct
Plant Range: Europe to Siberia & Caucasus

How to Grow

Cultivation

Grow in almost any well-drained soil in full sun. Thrives in poor soils but will not tolerate waterlogging

Propagation

Propagate by seed or by division, separating rhizomes in autumn

Suggested planting locations and garden types

Coastal
Cottage and informal garden
Prairie planting
Wildflower meadow
Wildlife gardens
Low Maintenance
Flower borders and beds

Pruning

Deadhead to encourage more flowers, unless seed is required

Pests

Generally pest-free

Diseases

May be susceptible to downy mildews, powdery mildews and rust diseases