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Herbaceous PerennialSynonym

Centaurea scabiosa var. petrophila
  • RHS Plants for pollinators

greater knapweed

An upright perennial to about 1.5m, with branched stems and greyish-green, broadly lance-shaped leaves to 25cm long, and reddish-purple flowers heads to 5cm across, usually with enlarged outer florets, from mid to late summer

Other common names
black top
pengaled fawr
Synonyms
Centaurea scabiosa var. petrophila
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Size
Ultimate height
1–1.5 metres
Time to ultimate height
2–5 years
Ultimate spread
0.5–1 metres
Growing conditions
Chalk
Loam
Sand
Moisture
Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green
Summer Red Purple Green
Autumn Green
Winter
Position
  • Full sun
Aspect

West–facing or South–facing or East–facing

Exposure
Exposed or Sheltered
Hardiness
H6
Botanical details
Family
Asteraceae
Native to GB / Ireland
Yes
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

How to grow

Cultivation

Prefers well-drained soil in a sunny position. Especially tolerant of dry alkaline soils

Propagation

Propagate by seed in spring, or propagate by division in spring or autumn

Suggested planting locations and garden types
  • Wildlife gardens
  • Wildflower meadow
  • Cottage and informal garden
  • Flower borders and beds
Pruning

Self-seeds readily so prune after flowering if seed is not required

Pests

Generally pest-free

Diseases

May be susceptible to Powdery mildews

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