Common knapweed is a tough, attractive, and easily grown hardy perennial flower, native to the British Isles. It's a superb wildlife plant as the flowers are rich in nectar and pollen, and attract bees, butterflies, and moths, while the seed heads are popular with seed-eating birds such as goldfinches. The pink-purple flowers look thistle-like at first glance, though knapweed is not prickly. The rounded flower heads are made up of many tiny flowers with ragged bracts, borne on stems to a metre high above clumps of long, entire or partly lobed, mid green leaves.
Knapweed is excellent for planting in flowering lawns, wildlife meadows, banks, and wilder areas, to bloom from midsummer to early autumn, followed by architectural seed heads on dead stems. As well as being widely known as black knapweed and hardhead, common knapweed has many local common names including iron knobs, black centaury, loggerheads, and Spanish buttons.
How to grow knapweed
Plant ready-grown knapweed plug or pot-grown plants, or sow seed, in autumn or spring. Leave the stems and seed heads over winter and cut back dead stems by early spring. Propagate by seed or division.
Where to grow knapweed
Knapweed can be grown almost anywhere. It thrives in a wide range of soils and situations, in full sun or partial shade. It tolerates cold exposed sites. It's tough and vigorous, able to grow well in grass, as well as on banks, woodland borders and naturalistic or wilder areas.
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How to plant knapweed
Knapweed is hardy and can be planted in autumn or spring, or in mild spells during winter. Plant singly or in informal clumps or drifts, with plants spaced 30cm apart. Water in after planting and keep moist during dry spells for the first few weeks until established.
How to care for knapweed
Knapweed is easy to grow and needs little care. Cut back the dead stems before new growth emerges in spring.
How to propagate knapweed
Collect knapweed seed when brown and ripe and sow on bare, moist soil where plants are to grow, covering with a thin layer of soil. Or allow plants to self-seed and transplant the young seedlings to their final planting position.
Divide established clumps whilst dormant, any time from autumn to early spring.
Growing knapweed: problem solving
Knapweed is a trouble-free plant to grow.
Advice on buying knapweed
- Seed of knapweed is widely available in the wildflower seed section of garden centres, or from mail order suppliers
- Pot grown plants may be available, although most likely to be found as young plants (plugs) to buy by mail order from suppliers of UK native (wild) plants