California · zones 7a–10b
When to plant onions in California.
Sow or transplant between Nov 6 to Dec 20 in a typical year, keyed to California's median last frost around Jan 14. A second, fall sowing fits Oct 19 to Nov 30. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical California season.
1 · Start indoors
Sep 25 to Nov 8
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Nov 6 to Dec 20
Keyed to the ~Jan 14 last frost. Sow 0.5" deep, 4" apart.
Fall round
Oct 19 to Nov 30
Counted back from the ~Dec 14 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
California spans more than one climate: Zone 10 is the most common zone, but the state runs 7a to 10b. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
California growing notes
California onions: your zip code sets the variety.
Short-day desert, intermediate valley, long-day mountains
No other state spans as much of the onion day-length map as California. The low desert around the Imperial Valley grows short-day onions that bulb on 10 to 12 hours of light and are usually planted in fall for a winter harvest; the coastal strip and most of the Central Valley sit in intermediate territory, bulbing at 12 to 14 hours; and the mountain and far-northern counties run long enough summer days to grow true long-day onions. Plant the wrong type for your region and the bulb stops growing at golf-ball size the moment day length triggers it, no matter how well you fed it.
Candy performs well through the intermediate middle of the state and sizes up to softball bulbs under good care, and Red Torpedo is another dependable intermediate-day pick for that same stretch. California Red, despite growing near the short-day desert valleys, is generally catalogued as an intermediate-day onion too, so group it with Candy and Red Torpedo rather than assuming the name means it belongs in desert country; gardeners in the far north or high Sierra foothills should look specifically for a long-day variety bred for 15-plus hour summer days, the kind sold for Pacific Northwest or Midwest gardens.
The leaf-count rule and steady feeding
Every leaf an onion grows before bulbing starts becomes one ring in the finished bulb, so the plant's whole job before the day-length trigger flips is stacking leaves. Set transplants 4 inches apart so roots are not competing for the nitrogen that builds that leaf count, and side-dress every 3 to 4 weeks until you see the neck start to soften, the visible signal that the plant has switched from leaf growth to bulb fill.
California's sandy coastal and valley soils drain fast, which means nitrogen washes past the root zone between waterings more than gardeners expect. A light, frequent feeding schedule beats one or two heavy doses; onions fed that way size up more evenly than ones that get a single spring application and are left alone after.
Thrips pressure and the cure that actually works
Onion thrips thrive in California's dry heat and show up as silvery scratches on the leaves, worst in inland gardens where humidity stays low through summer. Spraying the plant top to bottom, including down inside the neck where thrips hide from overhead water, controls them better than a single pass; insecticidal soap needs to actually contact the insect to work.
Once half the tops have fallen over on their own, stop watering and let the bulbs finish dry. California's low summer humidity is an advantage here: cure bulbs 2 to 3 weeks in a shaded, airy spot, and they dry down faster and store longer than the same variety would in a muggier state. A well-cured Candy holds about 3 months in a cool pantry, and a pungent variety like California Red or Red Torpedo will hold noticeably longer than that on the same shelf. Braid the dry necks or bag bulbs in mesh once cured, since the state's dry air also means bulbs left in a closed plastic bag sweat and rot far faster than they would simply sitting loose on a shelf.
In California: watch for
The pests that find onions here.
With about 334 frost-free days, onion, bulb spends longer in the ground here than in most of the country, which widens the window in which onion thrips can find it. Scout weekly from midseason and act on the first signs.
Silvery streaks and curled leaf tips in hot spells.
Organic fix: Insecticidal soap or neem; hang sticky traps.
Seedlings wilt; white maggots in the bulb base.
Organic fix: Float a row cover over the row; rotate beds each year.
Pale patches with fuzzy gray growth in damp weather.
Organic fix: Space for airflow, water early in the day, spray neem.
White rot
Yellowing and dieback, then wilt; fluffy white mold at the bulb base and roots so rotted the plant lifts straight out.
Organic fix: No cure once it is in the soil. Plant clean stock, never follow onions with onions, and keep infested soil off tools and boots.
Your season math: California gives onions about 334 frost-free days, and it needs roughly 95 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting onions in California: questions
When should I plant onions in California?+
In a typical California year, sow onions or set out transplants between Nov 6 to Dec 20, keyed to the state's median last frost around Jan 14. There's also a fall window: Oct 19 to Nov 30. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in California?+
Start seeds inside about 6 weeks before set-out: roughly Sep 25 to Nov 8 for a typical California season.
What USDA zone is California?+
California spans zones 7a–10b, mostly zone 10. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many onions plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.