Native to tropical America, mostly Mexico. Showy summer- and fall-blooming plants, open and branching in habit, with bright green, divided leaves and daisylike flowers in many colors and forms (single, double, crested, frilled). Heights vary from 212 to 8 ft. Use for mass color in borders or background, or as a filler among shrubs. Useful in arrangements if flowers are cut just after they open and placed immediately in deep, cool water. Sow seed in open ground where plants are to grow; or set out transplants from spring to summer. Plant in not-too-rich soil. Plants self-sow freely and attract birds and butterflies.
C. atrosanguineus. CHOCOLATE COSMOS. Perennial from tuberous roots; often grown as annual. Zones MS, LS, CS, TS; USDA 7-11. Where winters are colder, dig and store as for dahlias. Grows 22 ft. tall, 1 ft. wide, with coarsely cut foliage. Blooms in late summer and fall, with deep brownish red, nearly 2-in.-wide flowers with a strong perfume of chocolate (or vanilla). Attractive companion for silvery-foliaged plants. Provide well-drained soil. Winter mulch is prudent in all but mildest regions (where plant tends to be rather short lived). 'Choca Mocha' provides nice stands of burgundy flowers that are heat and drought tolerant once established.
C. bipinnatus. COMMON COSMOS. Annual. Heights up to 8 ft., widths to 12 ft. Blossoms are 34 in. wide, with tufted yellow centers and rays in white and shades of pink, rose, lavender, purple, or crimson. Among the many types are 3- to 4-ft.-tall 'Candystripe', with white-and-rose flowers; 'Picotee', to 2 ft. high, white flowers edged red; 'Cutesy Mix' has mixed colors on a 30- to 36-in. plant; Sensation strain, 36 ft. tall, including 'Dazzler' (crimson) and 'Radiance' (rose with red center); 'Double Dutch White' with large white double flowers standing 3-4 ft. tall; 'Rose BonBon' with large double, rosy lavender flowers that stand 4 ft. tall; 'Sea Shells', to 3 ft. tall, grown for quilled ray flowers that look like long, slender cones; and 'Sensation Pinkie Pink' has deep pink flowers on 36- to 48-in.-tall plants. 'Cosimo Collarette' has pink flowers fading to white on a 2-ft.-tall plant. Sonata is a dwarf strain 12 ft. high; 'Sweet Dreams' reaches 3 ft. tall and has pale pink-to-white blossoms with rose centers. Versailles mix, bred for cut flowers, reaches 3 ft. and bears its blossoms on long, strong stems. 'Sweet Sixteen' with light pink to white flowers with a darker pink edge is also used for cutting.
C. sulphureus. YELLOW COSMOS. Annual. To 7 ft. tall, 12 ft. wide, with yellow-centered, yellow or orange-yellow single flowers. Tends to become weedy looking at end of season. Two 3- to 4-ft.-tall, semidouble-flowering strains are Bright Lights, with 3-in. flowers in yellow, gold, orange, and orange-red; and Klondike strain, with 2-in. flowers ranging from scarlet-orange to yellow. Dwarf Klondike or Sunny strain is 1 ft. tall, bears 1-in. flowers. Foot-tall semidouble bloomers include Ladybird mix, with 2-in. scarlet, yellow, and orange flowers; and 'Sunny Red', with orange-red blooms. 'Cosmic' series, available in orange, red, and yellow have a branched habit on compact, 12-in. plants; tolerate poor soil, heat, and humidity.