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Genus Centaurea (Hardheads, Knapweed)

Centaurea Centaurea montana Photo/Illustration: Steve Aitken
sen-TOR-ee-ah Common Name: Hardheads, Knapweed
Centaurea is a large genus of about 450 species of annuals, biennials, perennials, and subshrubs from mostly dry sites, mainly in Europe and the Mediterranean. They are cultivated for their fringed flowers in shades of pink, yellow, white, and true blue. The bracts often have toothed or spiny tips in white or black. Use Centaurea in borders, rock gardens, as bedding, or for naturalizing.
 Noteworthy characteristics: Fringed flowers that are attractive to bees and butterflies. Good cut flowers.
 Care: Most species will grow in any well-drained soil in full sun and tolerate some drought. C. macrocephala and C. montana need moist soil.
 Propagation: Sow annual seeds where they are to grow or in peat pots in spring; sow perennial seed in a cold frame in spring. Divide in spring or autumn.
 Problems: White mold, rust, downy and powdery mildew, thread blight, Southern blight.

Species, varieties and cultivars for genus Centaurea

Centaurea cineraria 'Colchester White' Centaurea cineraria 'Colchester White'
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Hardiness Zones: 1 2 3 4 5 6 7 8 9 10 11

Best used as a foliage plant, this plant's intricately cut, frosty-silver leaves produce a large, elegant arching mound. It also bears pale lavender-blue pin-cushion flowers on lanky 30-inch stems in late spring.
Centaurea cyanus Centaurea cyanus
(Bachelor's buttons, Bluebottle, Cornflower) Be the first to rate this plant
Hardiness Zones: 1 2 3 4 5 6 7 8 9 10 11

Bachelor's buttons bear charming and prolific flowers in hues of blue, pink, lavender, white, and maroon. Those with a true blue color are especially welcome in the garden as that color is rare in nature. Each disc-shaped flower is about 1.5 inches across, with ragged petals radiating out from the center.
Centaurea macrocephala Centaurea macrocephala
(Giant knapweed, Yellow hardhead) (2 user reviews)
Hardiness Zones: 1 2 3 4 5 6 7 8 9 10 11

This clumping, robust perennial has unusual ramrod-stiff flower stems that bloom from early summer through late summer. Its fat, rusty buds open into large, deep yellow thistle flowers the size of a small fist. Easy to cut and dry for arrangements. This plant has big, coarse leaves that call for strong companions.
Centaurea montana Centaurea montana
(Mountain bluet) (3 user reviews)
Hardiness Zones: 1 2 3 4 5 6 7 8 9 10 11

Mountain bluet is an excellent choice for the border or rock garden. Blue flowers open from attractive buds in late spring to midsummer, then leave behind a mass of vigorous, silvery-green woolly foliage and woolly stems.
Centaurea montana ‘Amethyst in Snow’ Centaurea montana ‘Amethyst in Snow’
(Mountain bluet) Be the first to rate this plant
Hardiness Zones: 1 2 3 4 5 6 7 8 9 10 11

The blooms of this familiar perennial are not the standard blue; instead, they’re a striking silky white with royal purple centers. The flowers appear in late spring, then leave behind a mass of vigorous silvery green foliage.