When to plant Cosmos in Zone 3a
In Zone 3a, Cosmos: direct sow outdoors around May 25–Jun 8. Expect to harvest around Jul 24–Aug 7.
| Step | When |
|---|---|
| Direct sow outdoors | May 25 – Jun 8 |
| Harvest | Jul 24 – Aug 7 |
Tip: Thrives on neglect — too-rich soil gives leaves at the expense of flowers.
Zone 3a averages a last spring frost around May 25 and a first fall frost around Sep 8. These are zone averages — look up your ZIP for your exact area.
See the full Zone 3a calendar in the tool →