When to plant Rosemary in Zone 4a
In Zone 4a, Rosemary: start seeds indoors around Mar 6–Mar 20; transplant outdoors around May 29–Jun 12. Expect to harvest around Aug 27–Sep 10.
| Step | When |
|---|---|
| Start seeds indoors | Mar 6 – Mar 20 |
| Transplant outdoors | May 29 – Jun 12 |
| Harvest | Aug 27 – Sep 10 |
Tip: Slow from seed and frost-tender in cold zones — most gardeners start from a plant and overwinter indoors.
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 →