Growing Tips: Cosmos

Quick Reference:

Annual, a plant that completes it’s life cycle in one season. Germinates in 5 to 10 days at an optimum soil temperature of 72 degrees F. Cover seed with 1/8 inch fine soil spaced ½ to ¾ inches apart. Ideal spacing in the garden is 16 to 24 inches. Plant height: 30 to 36 inches.

When and where to plant:

Select a sunny location and plant cosmos outdoors after all danger of frost is past. In Alaska for earlier bloom start indoors 5-7 weeks before last frost. Fill a container that has drainage holes with a sterilized potting soil, sprinkle seed on soil surface, cover seed lightly with fine soil, water well for good seed-soil contact and keep moist at all times until seedlings emerge. When seedlings show their first green leaves water with a liquid solution of plant food. Soon after the seedlings have their first true leaves transplant to individual plastic pots, keep moist, water with a liquid solution of plant food every two weeks and grow in a sunny area until the garden is ready. Transplant to the garden after the last frost. When planting directly in the garden, cultivate, smooth soil surface with rake, scatter seeds evenly over planting area, cover seed lightly with soil, water well for a good seed-soil contact and keep moist until seedlings emerge. In the garden, seedlings grown from a direct seeded planting can be carefully transplanted for better spacing.


Requires little care. Avoid overhead watering when possible.