Centaurea – Knapweed, Hardy Cornflower, Hardheads, Mountain Bluet The Centaureas are some of the most graceful flowers to grow in any garden. The flower heads are like showy, ragged thistle blooms of bright red, deep purple, golden yellow and blue. They grow from 2 feet to 3 1/2 feet tall and bloom during the Summer months. SPECIES. The Golden Knapweed […]