Rosemary in Zone 4a & 4b
Salvia rosmarinus
When to plant rosemary in zone 4b
Zones 4a and 4b share the same average frost dates in our data, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. Rosemary 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.
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.
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
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 · Full companion planting guide · Full plant profile · 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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