Centaurea jacea aka Brown Knapweed

Centaurea jacea is known as brown knapweed or brownray knapweed. It belongs to the daisy family, Asteraceae. Its native range spans Europe, western Siberia and the Caucasus. It is not native to Britain or Ireland. This perennial grows in temperate regions. Wild plants occur along hedges, on unused land and waste ground.

The plant forms vigorous clumps and loses its leaves seasonally. Garden plants reach 3.3–4.9 feet [1–1.5 metres] tall. Their spread reaches 1.6–3.3 feet [0.5–1 metre]. Plants take two to five years to reach full size. The green leaves have a narrow, lance-shaped outline. Fine white hairs coat both the leaves and stems. These give the plant a felted surface.

Flowers appear in summer, in shades of mauve-pink or lilac. Overlapping brown bracts wrap each bud before it opens. Long white hairs fringe the edges of these bracts. Each open head has many small flowers at its centre. Longer, narrow outer florets form a ring around them. Remove spent heads to help the plant produce more flowers. Leave some heads in place when seed is needed. Propagate it from seed or divide its rhizomes in autumn.

Give brown knapweed full sun and soil that drains well. It grows in poor ground and tolerates drought. Suitable soils include chalk, loam and sand. Acid, neutral and alkaline conditions all suit it. Avoid waterlogged ground, which it does not tolerate. Both exposed and sheltered sites can suit this plant. The RHS rates its hardiness as H6. This covers winter lows of about −20 to −15°C. Plants For A Future lists USDA zones 5–9. Suggested settings include coastal gardens, informal borders and prairie-style planting. It also suits wildflower meadows and gardens planned for wildlife.

Pests seldom cause trouble, though several fungal diseases can occur. These include downy mildew, powdery mildew and rust. Plants For A Future flags the plant as potentially weedy. It records young leaves as a cooked vegetable. That source gives its edible value a low rating. It also reports traditional uses for roots and leaves. These include digestive remedies and a leaf-based eye wash. Such records do not establish safe or effective treatment. The source lists no known hazards, rather than proven safety.