Zone 9a covers 32 days of last-frost dates. We measured Mobile, AL at Feb 3 and Seattle, WA at Mar 7. 1 of the 10 places we checked in this zone doesn't dependably freeze at all. 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 9a
Zone 9a's last spring frost averages Feb 12 and first fall frost Dec 3 — about 294 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 9a?
Onion matures in about 90–110 days from sowing. In zone 9a that means sowing around Jan 29 and first picking around Apr 29.
Will onion survive frost in zone 9a?
Yes — onion tolerates light frost. In zone 9a you can sow a little before the last frost (around Feb 12) and keep harvesting past the first fall frost (around Dec 3).
For soil, spacing, pests and companion planting, see the full onion growing guide →