Sulphur Cosmos

Overview. Sulphur cosmos is a fast growing annual with golden-yellow or orange flowers. It is also called yellow cosmos, orange cosmos and Klondike cosmos.

Its flowers come in many tones of yellow, orange and red, and it is a half-hardy annual. It is native to Mexico to Central America.

Plant size varies by selection. Most are 50 cm to 1 m tall (about 20 inches to 3.3 feet), with some dwarf forms. Some taller types can reach 6 feet (1.8 m).

When and how to sow. Sow seeds outdoors after the danger of frost has passed. Wait until the soil has warmed to at least 65°F (18°C). Rake the seeds into loose soil and don’t plant them too deeply, because deep planting slows germination.

Germination. Keep the soil moist for 5 to 10 days after sowing. Seeds germinate in 7 to 21 days.

Site and soil. Give it full sun, meaning 6 or more hours of direct sun a day. It grows in moderately fertile, moist but well-drained soil.

Containers and staking. It is suited to patio and container planting. Taller varieties may need staking in high winds and frequent storms.

Uses. Use it in the background as a bedding plant or in a cut flower garden.

Deadheading. Deadheading regularly keeps it flowering longer.

Re-blooming. Cut plants back to 12 to 18 inches (30 to 46 cm) high to encourage new blooms; they should be back in bloom in about a month.

Water. It tolerates dry soils.

Pests and diseases. Aphids and Japanese beetles are occasional pests, and bacterial wilt and canker are occasional diseases. Aphids and slugs may be a nuisance, and grey moulds may be a problem.

Reseeding. It reseeds easily and can become weedy.