When to plant Cosmos in Zone 4a
In Zone 4a, Cosmos: direct sow outdoors around May 15–May 29. Expect to harvest around Jul 14–Jul 28.
| Step | When |
|---|---|
| Direct sow outdoors | May 15 – May 29 |
| Harvest | Jul 14 – Jul 28 |
Tip: Thrives on neglect — too-rich soil gives leaves at the expense of flowers.
Zone 4a averages a last spring frost around May 15 and a first fall frost around Sep 18. These are zone averages — look up your ZIP for your exact area.
See the full Zone 4a calendar in the tool →