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. Winter Squash is frost-sensitive, so the 2w after 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 3 weeks ahead gives strong transplants ready the moment the soil warms.
Common questions
How long does winter squash take to grow in zone 4b?
Winter Squash matures in about 80–110 days from sowing. In zone 4b that means sowing around May 18 and first picking around Aug 6.
Will winter squash survive frost in zone 4b?
No — winter squash 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 winter squash growing guide →