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Herbaceous PerennialSynonym

Grossheimia macrocephala
  • RHS Plants for pollinators

giant knapweed

A large, clump-forming perennial with simple or lobed leaves and yellow flower-heads 5cm across opening in summer from brown buds

Other common names
great-headed centaury
Synonyms
Grossheimia macrocephala
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Size
Ultimate height
1–1.5 metres
Time to ultimate height
2–5 years
Ultimate spread
0.1–0.5 metres
Growing conditions
Chalk
Clay
Loam
Sand
Moisture
Moist but well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green
Summer Yellow Green
Autumn Green
Winter
Position
  • Full sun
  • Partial shade
Aspect

West–facing or South–facing or North–facing or East–facing

Exposure
Exposed or Sheltered
Hardiness
H7
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
Caucasus

How to grow

Cultivation

Best grown in moist but well-drained soil in sun or partial shade

Propagation

Propagate by seed sown in pots in a cold frame in spring or propagate by division in spring or autumn

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

Deadhead regularly to prolong flowering

Pests

Generally pest-free

Diseases

May be affected by powdery mildews

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