When to plant onion in zone 10a — planting calendar

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Showing USDA Zone 10A

Growing SeasonZone 10a

Last frost ~Jan 31First frost ~Dec 15Today

Start indoorsTransplant / sowHarvestFrost risk

NOVDECJANFEBMARAPRMAY

Start indoors Nov 22 · Sow Jan 17 · First harvest Apr 17 · Wrap by May 15

Last spring frostJan 31

Start seeds indoorsNov 22

Direct sowJan 17

First harvestApr 17

Last harvestMay 15

First fall frostDec 15

Why these dates work in zone 10a

Zone 10a's last spring frost averages Jan 31 and first fall frost Dec 15 — about 318 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 10a?

Onion matures in about 90–110 days from sowing. In zone 10a that means sowing around Jan 17 and first picking around Apr 17.

Will onion survive frost in zone 10a?

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

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