California planting calendar

When to plant onions in California — sow, transplant & harvest dates

California is mostly USDA zone 9b (range 5a-11a). Dates below are derived from onions's frost tolerance and California's frost window — not generic national averages.

Onions planting timetable for California

Stage	When in California	Anchor
Direct-sow / set out (main)	October — February	Grown through the cool season, not summer
Shoulder sowing	September and again late February	Avoid germinating into summer heat
First harvest	~110 days after sowing (late autumn through spring)	110-day crop

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why California's climate shifts the onions dates

California flips the calendar: its winter is the productive onions season while northern states are frozen, and its summer is the off-season. California packs more climate diversity than almost any state — alpine mountains, Mediterranean coast, Central Valley farmland, and desert. Coastal and valley areas grow year-round.

Onions are day-length sensitive: long-day varieties (zones 1–6) begin bulbing when days exceed 14 hours, short-day types (zones 7–10) bulb at 10–12 hours, and intermediate-day varieties span zones 5–6. Start seeds indoors 10–12 weeks before the last spring frost and transplant out 4–6 weeks before it — young onion seedlings tolerate frost down to about -6 °C once hardened off. In zones 8–10 a second planting from sets in autumn is common, overwintering for an early-summer harvest.

Frost-risk note

Light frost in the high Sierra Nevada (zone 5a-6a) only nips the outer leaves — heat, not cold, ends the crop.

Regional variation within California

the southern coast and Imperial Valley (zone 11a) can sow earliest in autumn and latest into late winter; the high Sierra Nevada (zone 5a-6a) has a slightly shorter, frost-bracketed window.

Los Angeles — USDA zone 10b
San Francisco — USDA zone 10b
Sacramento — USDA zone 9b
San Diego — USDA zone 10b
Fresno — USDA zone 9b

What else to plant in California around then

The same cool window suits other greens, brassicas, peas, carrots, and radishes — fill beds October through February.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 10-35 °C (50-95 °F).
Spacing: 4-6 inches (10-15 cm) between plants.
Days to harvest: ~110 days from planting out.

Frequently asked questions

When is the best time to plant onions in California?

In California (mostly USDA zone 9b), grow onions as a cool-season crop: direct-sow from October through February, harvest ~110 days later, and skip summer entirely — heat above 24 °C bolts it. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is California?

Most of California sits in USDA hardiness zone 9b, with the state spanning roughly 5a-11a from the high Sierra Nevada (zone 5a-6a) to the southern coast and Imperial Valley (zone 11a). The last spring frost averages mid-February (coast) to late April (interior) and the first fall frost mid-November (coast) to mid-October (interior).

Can you grow onions in California?

Yes. California's dominant zone 9b supports onions — the key is timing. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across California?

the southern coast and Imperial Valley (zone 11a) can sow earliest in autumn and latest into late winter; the high Sierra Nevada (zone 5a-6a) has a slightly shorter, frost-bracketed window.

What else can I plant in California around the same time?

The same cool window suits other greens, brassicas, peas, carrots, and radishes — fill beds October through February.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.