When to plant Cosmos in Zone 10b
In Zone 10b, Cosmos: direct sow outdoors around Jan 15–Jan 29. Expect to harvest around Mar 16–Mar 30.
| Step | When |
|---|---|
| Direct sow outdoors | Jan 15 – Jan 29 |
| Harvest | Mar 16 – Mar 30 |
Tip: Thrives on neglect — too-rich soil gives leaves at the expense of flowers.
Zone 10b averages a last spring frost around Jan 15 and a first fall frost around Dec 31. These are zone averages — look up your ZIP for your exact area.
See the full Zone 10b calendar in the tool →