How to Grow Cosmos

Cosmos bipinnatus

Cosmos is an old-fashioned favorite that bears clouds of blossoms in flowers above feathery foliage.

Cosmos can be started from seed indoors and transplanted into the garden two or three weeks after the last frost in spring. It will bloom from late spring into autumn.

Cosmos wants full sun and well-drained soil.

Get to Know Cosmos

  • Plant type: Annual
  • Growing zones and range: Summer annual in all zones
  • Hardiness: Tender
  • Height and width: 1 to 6 feet tall, 10 to 36 inches (25-91cm) wide depending on the variety
  • Flowers: Broad, silky rays of yellow, orange, scarlet, pink, deep rose, and white.
  • Bloom time: Summer
  • Uses: Mass in beds and borders; very good cutting flower.
  • Botanical name: Cosmos spp.
  • Common name: Cosmos

Where to Plant Cosmos

  • Plant Cosmos in full sun or partial shade.
  • Cosmos will grow in poor to average, well-drained soil.
Cosmos in the garden
Cosmos in the garden

When to Plant Cosmos

  • Set Cosmos seedlings in the garden after all danger of frost has passed in spring.
  • Sow seed directly in the garden after the last frost.
  • Pinch out the plants’ tops when they are a few inches tall to encourage bushier growth.

Planting and Spacing Cosmos

  • Space Cosmos 10 inches (25cm) apart.

How to Water and Feed Cosmos

  • Cosmos requires moderate water; water as needed. Cosmos can tolerate drought.
  • Cosmos does not need feeding; prepare the planting bed in advance by adding plenty of aged compost or commercial organic planting mix.

Cosmos Care

  • Stake Cosmos as needed.
  • Trim spent blooms to promote more blooms.
  • Cosmos is commonly pest and disease-free.

Cosmos Varieties to Grow

  • Cosmos bipinnatus ‘Sensation’ is a classic strain with white and pink flowers that can grow to 10 feet (3m) tall.
  • ‘Sonata’ is compact 2-foot tall flowers in pink, deep rose, white.
  • C. sulphureus ‘Bright Lights’ grow to 3 feet (.9m) tall and has yellow, orange, and scarlet flowers.

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