Zone 4b covers 52 days of last-frost dates. We measured Pierre, SD at Apr 28 and Jackson, WY at Jun 19. Give us your town or ZIP and we'll use ten years of daily lows recorded at your own coordinates instead of the middle of that range.
Why these dates work in zone 4b
Zone 4b's last spring frost averages May 4 and first fall frost Oct 20 — about 169 frost-free days. Borage 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.
Common questions
How long does borage take to grow in zone 4b?
Borage matures in about 50–70 days from sowing. In zone 4b that means sowing around May 4 and first picking around Jun 23.
Will borage survive frost in zone 4b?
No — borage is frost-sensitive. In zone 4b, wait until after the last frost (around May 4) to plant, and harvest before the first fall frost (around Oct 20).
For soil, spacing, pests and companion planting, see the full borage growing guide →