When to plant Cosmos in Zone 4b
In Zone 4b, Cosmos: direct sow outdoors around May 10–May 24. Expect to harvest around Jul 9–Jul 23.
| Step | When |
|---|---|
| Direct sow outdoors | May 10 – May 24 |
| Harvest | Jul 9 – Jul 23 |
Tip: Thrives on neglect — too-rich soil gives leaves at the expense of flowers.
Zone 4b averages a last spring frost around May 10 and a first fall frost around Sep 22. These are zone averages — look up your ZIP for your exact area.
See the full Zone 4b calendar in the tool →