Description
Centaurea – Hardheads – Knapweed – Cornflower –
There about 450 species of annuals, biennials, perennials and subshrubs, in this genus. They occur in dry sites, including woodland, rocky mountain slopes, subalpine meadows, and sand dunes mainly in Europe and the Mediterranean with a few in Asia, Australia and North America. The simple leaves are pinnatisect or pinnatifid, and sometimes silvery hairy. They bears spherical or hemispherical flowers with tubular, usually deeply lobed florets, the outer ones often larger and more spreading than the rest, in shade of blue, red, pink, purple, and yellow. Each flower has a conspicuous involucre, the bracts overlapping, fringed, and often with toothed or spiny, silvery white or black tips. Grow in a border or rock garden, some are ideal for naturalizing in grass or in a wildflower garden. Some perennial are grown as summer bedding annuals. All are attractive to bees and butterflies, and many provide excellent cut flowers.
Grow in well drained soil in full sun. Divide in spring or fall.
Prone to white mold, rust, downy mildew, powdery mildew, thread blight, and southern blight.
C. rothrockii – This multi stemmed hardy annual or biennial from the Southwestern USA and Northern Mexico grows 3-5′ feet tall and 3′ feet wide. It produces lance shaped, usually hairless leaves, to 5″ long. From summer to autumn it bears pale purple to pink flowers, 4-5″ across, with off white to yellow centers. The basket like seed heads are attractive in arrangements
Zones 6-10
