Zone 6a covers 28 days of last-frost dates. We measured Omaha, NE at Apr 14 and Flagstaff, AZ at May 12. 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 6a
Zone 6a's last spring frost averages Apr 22 and first fall frost Nov 1 — about 193 frost-free days. Onion tolerates light frost, so you can sow ahead of the last-frost date and keep harvesting into the cooler fall. Starting seeds indoors 10 weeks ahead gives strong transplants ready the moment the soil warms.
Common questions
How long does onion take to grow in zone 6a?
Onion matures in about 90–110 days from sowing. In zone 6a that means sowing around Apr 8 and first picking around Jul 7.
Will onion survive frost in zone 6a?
Yes — onion tolerates light frost. In zone 6a you can sow a little before the last frost (around Apr 22) and keep harvesting past the first fall frost (around Nov 1).
For soil, spacing, pests and companion planting, see the full onion growing guide →