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Flowers · tender annual
Cosmos from seed
Cosmos bipinnatus
- Germination temperature
- 68 to 72°F (20 to 22°C)
- Sowing depth
- covered lightly
- Days to germinate
- 5 to 10 days
- Light
- Cover the seed; darkness helps
- Before sowing
- Nothing needed
- Start indoors
- 4 to 7 weeks before planting out
- Plant out
- 0 to 2 weeks after the last frost
- Sow outdoors
- 1 to 2 weeks after the last frost
Your dates from your last frost Seed not coming up?
Sowing
Johnny's: 7 to 10 days at 68 to 72°F. Cover seed lightly; sow direct after the last frost once soil is above 60°F (16°C), or start indoors 5 to 7 weeks ahead.
Care and transplanting
Pinch to encourage branching. Cosmos thrive on poor soil; rich soil gives leaves, not flowers.
Problems
Tall plants flop without support. Too much feed means few flowers.
Saving seed
Collect dry seeds from spent heads; cosmos self-sow.