Greater Knapweed

Description

Centaurea scabiosa – greater knapweed

Botanical name: Centaurea scabiosa
Common names: Greater knapweed
Family: Asteraceae (daisy family)
Plant type: Herbaceous perennial
Habit: Upright, clump-forming
Pot size: 2–3 litre pot
Eventual size: Approx. 60–90cm tall × 45cm spread
Foliage: Deeply divided, coarse, dark green leaves; deciduous
Flowers: Large, fringed, thistle-like rich purple-magenta flowerheads on stout stems through summer (June–September)
Scent: Not notably scented
Aspect / light: Full sun
Soil: Well-drained; poor to average; thrives on chalk and lime; drought-tolerant; any pH
Hardiness: RHS H7 (very hardy, below −20°C); USDA zones 4–8
Exposure: Open, sunny; very tolerant
Native range: Native to Europe including the UK
Toxicity / pet & child safety: Generally considered non-toxic to people and pets

Centaurea scabiosa, greater knapweed, is a handsome native wildflower with large, fringed purple-magenta thistle-like flowers all summer. Tough, chalk-loving and one of the very best plants for pollinators.

GardenAdvice notes

One of the finest of all native wildflowers for pollinators, greater knapweed produces large, richly coloured purple-magenta flowerheads with beautifully fringed, ragged petals through summer, held on stout stems above deeply divided foliage. A plant of chalk grassland and roadside verges, it is tough, deep-rooted and drought-tolerant, and its nectar-rich flowers are absolutely alive with bees and butterflies — followed by seedheads that feed goldfinches.

Growing & planting

Plant in spring or autumn in well-drained soil in full sun — it thrives on poor, dry, chalky and limy soils and is very tolerant. Ideal for wildflower meadows, chalk grassland, wildlife and naturalistic borders, and gravel. Space about 45cm apart. It has a deep taproot and dislikes being moved once settled.

Care & maintenance

Very low-maintenance. Deadhead to prolong flowering if wished, but leave the later seedheads standing, as goldfinches and other birds feed on them. Cut down old growth in late winter. It self-seeds gently in suitable ground. Water only while establishing; thereafter it is drought-tolerant.

Propagation

• Seed: Sow fresh seed in autumn, or allow it to self-seed gently.
• Division: Can be divided in spring, though the deep taproot resents disturbance.

Pests & diseases

Generally trouble-free and very tough. Powdery mildew occasionally occurs in dry spells. Otherwise little troubled by pests or disease — a robust native.

Uses in the garden

Superb in wildflower meadows, chalk grassland, wildlife gardens, naturalistic and gravel borders, where its large fringed purple flowers bring a long, informal display and feed vast numbers of pollinators.

Wildlife value

One of the very best native plants for wildlife: the nectar-rich flowerheads are hugely attractive to bees, butterflies, moths and hoverflies through summer, and the seedheads are a favourite food of goldfinches.

Toxicity & safety

Greater knapweed is generally regarded as non-toxic to people and pets.

GardenAdvice tip

If you want to do one thing for pollinators, plant greater knapweed — its big fringed purple flowerheads are among the very best nectar sources of any native plant, alive with bees and butterflies all summer. Then leave the seedheads standing into autumn and the goldfinches will come for them. It loves poor, dry, chalky soil, so don’t pamper it.

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