Annual forms of Centaurea are grown mainly for cut flowers; perennial kinds are valued principally for their soft, silvery foliage. All are relatively easy to grow. For best performance, add lime to acid soils. In most cases, plan to sow seeds of annuals or set out plants of perennial kinds in spring (or in fall, in mild-winter areas).
C. americana. BASKET FLOWER. Annual. Zones US, MS, LS, CS, TS; USDA 6-11. Native to central and southwestern U.S. Grows to 56 ft. high, 3 ft. wide, with rather rough, oval leaves to 4 in. long. Blooms in summer; flower heads to 4 in. wide are rose-pink, paler toward center. Good in arrangements, fresh or dried.
C. cineraria (C. gymnocarpa). DUSTY MILLER. Perennial in Zones LS, CS, TS; USDA 8-11; annual anywhere. (This common name applies to many plants with whitish to silvery white foliage.) From Italy. Compact plant grows to 1 ft. wide, 1 ft. or taller. Velvety white, 3- to 6-in. leaves, mostly in basal clump, are strap shaped, with broad, roundish lobes. Solitary 1-in. flower heads (purple, occasionally yellow) in summer. Trim back after flowering. Attracts bees. Not browsed by deer.
C. cyanus. BACHELOR'S BUTTON, CORNFLOWER. Annual. Zones US, MS, LS, CS, TS; USDA 6-11. Native to northern temperate regions. Grows 1212 ft. tall and less than a foot wide; will send out branches if given sufficient space. Narrow, gray-green leaves are 23 in. long; spring to midsummer flowers are 1112 in. wide, in blue, pink, rose, wine-red, white. Blue forms are traditional favorites for boutonnieres. Bushy, compact 'Jubilee Gem' reaches just 1 ft. high, has deep blue blooms; Polka Dot strain has all the typical cornflower colors on 16-in. plants. 'Black Ball' has dark crimson double flowers on 1- to 2-ft. stems. Sow seed in late summer or fall.
C. dealbata. PERSIAN CORNFLOWER. Perennial. Zones US, MS, LS; USDA 6-8. Native to the Caucasus. Forms an upright, bushy clump 23 ft. tall and about as wide. Deeply cut leaves to 8 in. long are deep green above, silvery beneath. In midsummer, leafy stems bear thistlelike pink blossoms to 112 in. across; they make long-lasting cut flowers. May require staking, especially if grown in rich soil. 'Steenbergii' is a compact selection just 12 ft. tall, with 2-in. blooms in rich carmine-pink.
C. hypoleuca 'John Coutts'. Perennial. Zones US, MS, LS; USDA 6-8. Variety of a species from Asia Minor. Looks something like C. montana but has more deeply lobed leaves and deep rose flower heads. Sometimes offered as a selection of C. dealbata.
C. macrocephala. GLOBE CENTAUREA. Perennial. Zones US, MS, LS; USDA 6-8. From the Caucasus. Leafy plant with coarse leaves 68 in. long; reaches 34 ft. tall, 2 ft. wide, with 2-in. clusters of yellow summer flowers tightly enclosed at the base by overlapping papery, shiny brown bracts. Flower heads resemble thistles. Use in fresh or dried arrangements.
C. montana. MOUNTAIN BLUET. Perennial. Zones US, MS, LS; USDA 6-8. Native to the mountains of central Europe. Forms clumps to 112 ft. tall and wide, with grayish green, broadly lance-shaped, 5- to 7-in.-long leaves. Flowers resembling ragged, 3-in. blue cornflowers top the stems in late spring to midsummer. Divide every other year. This is a cool-season plant and is less vigorous in warmer climates. Regular water. 'Alba' has white blooms. 'Amethyst Dream' has deep purple flowers. The two-toned 'Amethyst in Snow' sports white blooms with a deep purple center. 'Black Spider' has purplish-black flowers, with the outermost petals elongated and incurving.
C. moschata. SWEET SULTAN. Annual. Zones US, MS, LS, CS, TS; USDA 6-11. From Asia Minor. Erect plant, branching at base; grows to 2 ft. tall, 10 in. wide. Imperialis strain reaches 3 ft. high. Deeply toothed green leaves to 4 in. long. Thistlelike, 2-in. flower heads with a musky fragrance bloom from spring to fallmostly in shades of lilac through rose, but sometimes in white or yellow. Splendid cut flower. Sow seed directly on soil in spring or set out as transplants. Needs lots of heat.