When to plant Cosmos in Zone 3b
In Zone 3b, Cosmos: direct sow outdoors around May 20–Jun 3. Expect to harvest around Jul 19–Aug 2.
| Step | When |
|---|---|
| Direct sow outdoors | May 20 – Jun 3 |
| Harvest | Jul 19 – Aug 2 |
Tip: Thrives on neglect — too-rich soil gives leaves at the expense of flowers.
Zone 3b averages a last spring frost around May 20 and a first fall frost around Sep 12. These are zone averages — look up your ZIP for your exact area.
See the full Zone 3b calendar in the tool →