When to plant onion in zone 10b — planting calendar

Not your zone?

Showing USDA Zone 10B

Growing SeasonZone 10b

Last frost ~Jan 15First frost ~Dec 31Today

Start indoorsTransplant / sowHarvestFrost risk

OCTNOVDECJANFEBMARAPRMAY

Start indoors Nov 6 · Sow Jan 1 · First harvest Apr 1 · Wrap by Apr 29

Last spring frostJan 15

Start seeds indoorsNov 6

Direct sowJan 1

First harvestApr 1

Last harvestApr 29

First fall frostDec 31

Why these dates work in zone 10b

Zone 10b's last spring frost averages Jan 15 and first fall frost Dec 31 — about 350 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 10b?

Onion matures in about 90–110 days from sowing. In zone 10b that means sowing around Jan 1 and first picking around Apr 1.

Will onion survive frost in zone 10b?

Yes — onion tolerates light frost. In zone 10b you can sow a little before the last frost (around Jan 15) and keep harvesting past the first fall frost (around Dec 31).

For soil, spacing, pests and companion planting, see the full onion growing guide →