When to plant cosmos
Plant cosmos from the last spring frost to 2 weeks after it. Wait until the soil is at least 60°F. That works out to zone 5b (early May to mid May), zone 7a (mid April to late April) and zone 9a (early March to mid March).
Cosmos planting dates by zone
| Zone | Plant outdoors | cosmos ready from |
|---|---|---|
| 4a | May 15 – May 29 | Jul 21 |
| 4b | May 13 – May 27 | Jul 19 |
| 5a | May 11 – May 25 | Jul 17 |
| 5b | May 5 – May 19 | Jul 11 |
| 6a | Apr 30 – May 14 | Jul 6 |
| 6b | Apr 24 – May 8 | Jun 30 |
| 7a | Apr 15 – Apr 29 | Jun 21 |
| 7b | Apr 6 – Apr 20 | Jun 12 |
| 8a | Mar 27 – Apr 10 | Jun 2 |
| 8b | Mar 16 – Mar 30 | May 22 |
| 9a | Mar 2 – Mar 16 | May 8 |
| 9b | Feb 4 – Feb 18 | Apr 12 |
How to plant cosmos
| Plant as | seeds outdoors |
|---|---|
| Soil temperature | 60°F or warmer |
| Depth | 1/4 in |
| Spacing | 12–18 in |
| Light | Full sun |
| Time to bloom | 60–90 days |
Cosmos flower best in lean soil; too much fertilizer gives leaves, not blooms.
They often reseed.
Tall varieties may need staking.
Cosmos bipinnatus gives the classic pink and white flowers; Cosmos sulphureus has yellow and orange flowers and handles more heat.
Cut stems when flowers are just opening for vases that last about a week.
Goldfinches eat the seeds, so leave a few heads in fall.
When to expect flowers from cosmos
Deadhead or cut for vases to keep plants blooming.
Exact dates for your town: planting calendar · frost dates by state.
More flowers to plant
Begonias · Coleus · Marigolds · Zinnias · Sunflowers · Mums · Lantana · Hydrangeas