Why these dates work in zone 3b
Zone 3b's last spring frost averages May 6 and first fall frost Oct 22 — about 169 frost-free days. Rosemary is frost-sensitive, so the around last frost timing builds in a safety margin against a late cold snap — setting plants out too early risks losing them to frost. Starting seeds indoors 10 weeks ahead gives strong transplants ready the moment the soil warms.
Common questions
How long does rosemary take to grow in zone 3b?
Rosemary matures in about 80–100 days from transplanting. In zone 3b that means setting plants out around May 6 and first picking around Jul 25.
Will rosemary survive frost in zone 3b?
No — rosemary is frost-sensitive. In zone 3b, wait until after the last frost (around May 6) to plant, and harvest before the first fall frost (around Oct 22).
For soil, spacing, pests and companion planting, see the full rosemary growing guide →