Rosemary in Zone 4a & 4b
Salvia rosmarinus
Yes, rosemary grows in zones 4a and 4b. Start seeds indoors Mar 6–Mar 13 and plant out May 29–Jun 5.
When to plant rosemary in zone 4b
Zones 4a and 4b share the same average frost dates, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. It needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Mar 6–Mar 13 |
|---|---|
| Direct sow / transplant outside | May 29–Jun 5 |
| Estimated harvest | Aug 27–Sep 3 (~90 days after transplanting) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 2-4 ft.
Plant alongside it in zone 4b
These go outside within two weeks of rosemary in zone 4b, so one planting day can cover them.
- BasilMay 29–Jun 5
- BorageMay 15–May 22
- SageMay 29–Jun 5
- TobaccoMay 29–Jun 5
- Za'atar OreganoMay 29–Jun 5
- CatmintMay 22–May 29
Rosemary is a woody Mediterranean shrub, not a tender annual herb. Treat it more like a small perennial landscape plant than something you replant every spring. In the right climate, one plant can keep producing for years.
How rosemary fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Rosemary needs about 90 days from transplant to first harvest.
Rosemary planting windows in every zone
Zone 4b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Harvest |
|---|---|---|---|
| 4a & 4b (your zone) | Mar 6–Mar 13 | May 29–Jun 5 | Aug 27–Sep 3 |
| 5a & 5b | Mar 1–Mar 8 | May 24–May 31 | Aug 22–Aug 29 |
| 6a & 6b | Feb 14–Feb 21 | May 9–May 16 | Aug 7–Aug 14 |
| 7a & 7b | Jan 30–Feb 6 | Apr 24–May 1 | Jul 23–Jul 30 |
| 8a & 8b | Jan 14–Jan 21 | Apr 8–Apr 15 | Jul 7–Jul 14 |
| 9a & 9b | Dec 7–Dec 14 | Mar 1–Mar 8 | May 30–Jun 6 |
| 10a & 10bSpring window | Not usually | Feb–Apr | ~90 days after transplanting |
| Fall window | Not usually | Oct–Nov | ~90 days after transplanting |
| 11a & 11b | Oct 23–Oct 30 | Jan 15–Jan 22 | Apr 15–Apr 22 |
Harvest dates are about 90 days after the sow or plant-out date, not after starting seeds indoors.
Good companions
- Cabbage: Rosemary's scent is reputed to deter cabbage moths, the same role thyme and sage play, though rosemary itself hasn't been specifically tested the way thyme and sage have: treat this as garden tradition rather than a directly measured result.
Where to buy rosemary seeds
Botanical Interests · True Leaf Market · Burpee · High Mowing Organic Seeds (each supplier's rosemary seeds)
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing rosemary" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Plan your beds in the Garden Designer →
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Growing Rosemary in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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