When to plant onion in zone 9b — planting calendar

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Showing USDA Zone 9B

Growing SeasonZone 9b

Last frost ~Feb 15First frost ~Dec 10Today

Start indoorsTransplant / sowHarvestFrost risk

NOVDECJANFEBMARAPRMAYJUN

Start indoors Dec 7 · Sow Feb 1 · First harvest May 2 · Wrap by May 30

Last spring frostFeb 15

Start seeds indoorsDec 7

Direct sowFeb 1

First harvestMay 2

Last harvestMay 30

First fall frostDec 10

Why these dates work in zone 9b

Zone 9b's last spring frost averages Feb 15 and first fall frost Dec 10 — about 298 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 9b?

Onion matures in about 90–110 days from sowing. In zone 9b that means sowing around Feb 1 and first picking around May 2.

Will onion survive frost in zone 9b?

Yes — onion tolerates light frost. In zone 9b you can sow a little before the last frost (around Feb 15) and keep harvesting past the first fall frost (around Dec 10).

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