Centaurea scabiosa aka Greater Knapweed

Centaurea scabiosa, or greater knapweed, belongs to the daisy family, Asteraceae. Other names include black top and pengaled fawr. Its native range covers Europe and temperate Asia. It is native to Britain and Ireland too. In the wild, it grows in pastures and along roadsides. It also grows at field edges, often on chalk. These open habitats suit its need for sun and good drainage.

This herbaceous perennial forms upright clumps with branched stems. 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 about two to five years to reach full size. The grey-green leaves have a broad lance shape. They can reach 0.8 feet [0.25 metres] long. The plant loses its leaves during the dormant season.

Reddish-purple flower heads appear from mid to late summer. Each head can span about 0.16 feet [0.05 metres]. The outer florets are often larger than those within. These flowers suit meadow planting and informal garden beds. The plant also fits cottage gardens and flower borders. Wildlife gardens can use it among other meadow plants. Plants For A Future records its value for attracting wildlife.

Give greater knapweed full sun and soil that drains well. It grows in chalk, loam, or sand. It accepts acid, neutral, and alkaline soil conditions. Dry alkaline ground suits it well. Its moisture range runs from dry to moist, with drainage remaining important. Both exposed and sheltered sites can suit the plant. The RHS rates its winter hardiness as H6. Plants For A Future lists USDA zones 4–8.

Sow seed in spring to raise new plants. Divide clumps in spring or autumn as another option. Plants seed themselves freely, so cut back after flowering to limit seedlings. The RHS reports few pest problems, though powdery mildew can occur. Plants For A Future lists no known edible uses or hazards. This does not establish that every part is safe to eat. The same source records past medicinal uses of roots and seeds. These included treatments intended to increase sweating and urine flow. The plant also featured in old ointments for wounds and skin infections. These records describe past use, rather than proving medical benefit.