Zone 5b covers 25 days of last-frost dates. We measured Davenport, IA at Apr 16 and Idaho Falls, ID at May 11. 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 5b
Zone 5b's last spring frost averages Apr 28 and first fall frost Oct 22 — about 177 frost-free days. Watermelon 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 4 weeks ahead gives strong transplants ready the moment the soil warms.
Common questions
How long does watermelon take to grow in zone 5b?
Watermelon matures in about 70–90 days from transplanting. In zone 5b that means setting plants out around May 12 and first picking around Jul 21.
Will watermelon survive frost in zone 5b?
No — watermelon is frost-sensitive. In zone 5b, wait until after the last frost (around Apr 28) to plant, and harvest before the first fall frost (around Oct 22).
For soil, spacing, pests and companion planting, see the full watermelon growing guide →