How to Grow Cosmos from Seed
Cosmos sprout in 7–10 days and bloom in 60–75 days. They thrive in poor soil — too much fertilizer means no flowers. They self-seed every year.
Cosmos are the easiest wildflower. They’re also the most generous self-seeder.
Step-by-Step
1. Direct sow after last frost. Or start indoors 4-6 weeks before.
2. Depth. 1/4 inch.
3. Spacing. 12-18 inches.
4. Sun. 6-8 hours.
5. Don’t fertilize. Poor soil = more flowers.
6. Stake tall varieties. 3-5 feet tall.
7. Let some self-seed. For next year.
Common Questions
Why are my cosmos leggy? Too much fertilizer or not enough sun.
Do they self-seed? Yes. Aggressively.
When do I cut them? When flowers are open but before they fade.
Can I grow them in containers? Yes. Dwarf varieties work.
Do they attract bees? Yes. Bees and butterflies love cosmos.
Do they need staking? Tall varieties may need support in wind.