Root Vegetable

When to Plant Onions in California

The backbone of the kitchen garden. Choose short-day, intermediate, or long-day varieties based on your latitude.

The Short Answer

California is the largest onion-producing state in the U.S., with the Imperial Valley and Central Valley growing onions commercially year-round. Home gardeners benefit from the same conditions — California's diverse climates support short-day, intermediate, and long-day varieties depending on location.

California Frost Dates

Your planting dates depend on which part of California you're in. Here are the frost date ranges by region:

Region Zones Last Frost (Spring) First Frost (Fall)
Northern California Mountains 5a, 5b, 6a, 6b May 1 - May 25 Sep 20 - Oct 15
Central Valley 9a, 9b Feb 10 - Mar 1 Nov 15 - Dec 5
Southern California Coast 10a, 10b, 11a Jan 1 - Feb 1 Dec 10 - Jan 1
Bay Area 9b, 10a Jan 20 - Feb 15 Nov 25 - Dec 15

Onions Planting Schedule for California

Northern California Mountains (Zones 5a, 5b, 6a, 6b)

Average last frost: May 1 - May 25 · Average first frost: Sep 20 - Oct 15

Start Seeds Indoors
10 wks before frost
Transplant Outside
4 wks before frost
Direct Sow
4 wks before frost

Central Valley (Zones 9a, 9b)

Average last frost: Feb 10 - Mar 1 · Average first frost: Nov 15 - Dec 5

Start Seeds Indoors
10 wks before frost
Transplant Outside
4 wks before frost
Direct Sow
4 wks before frost

Southern California Coast (Zones 10a, 10b, 11a)

Average last frost: Jan 1 - Feb 1 · Average first frost: Dec 10 - Jan 1

Start Seeds Indoors
10 wks before frost
Transplant Outside
4 wks before frost
Direct Sow
4 wks before frost

Bay Area (Zones 9b, 10a)

Average last frost: Jan 20 - Feb 15 · Average first frost: Nov 25 - Dec 15

Start Seeds Indoors
10 wks before frost
Transplant Outside
4 wks before frost
Direct Sow
4 wks before frost

Growing Onions in California

State-Specific Growing Tips

Southern California and Central Valley: plant short-day or intermediate varieties from October through December for spring harvest. Northern California and mountains: plant long-day varieties from February through March. Coastal: intermediate varieties from October through January. California's dry climate reduces the foliar diseases that plague onion growers in the humid East. Drip irrigation is efficient and prevents the wet foliage that promotes disease.

Recommended Varieties for California

Short-day: Granex, California Red. Intermediate: Candy, Super Star. Long-day (northern CA/mountains): Copra, Walla Walla (originally from Walla Walla, WA). UC Davis provides variety recommendations by region.

Common Challenges in California

Thrips are the primary pest year-round. Pink root in some soils. The key is choosing the correct day-length type for your region — this single factor determines success or failure.

Growing Tips

Day length triggers bulbing. Northern gardeners need long-day varieties. Southern gardeners need short-day varieties.

Companion Planting

Plant onions alongside these companions for better growth:

Carrots Lettuce Beets Tomatoes

Keep onions away from:

Beans Peas

The Bottom Line

Onions can be grown successfully in California with proper attention to regional frost dates and local growing conditions. Timing varies across the state — Northern California Mountains gardeners work with a last frost around May 1 - May 25, while Bay Area sees frost end around Jan 20 - Feb 15. Choose varieties suited to your region, amend your soil based on its specific needs, and monitor for the pests and diseases most common in your area. For exact dates based on your zip code, use our free planting date finder.

Related Guides

Onions Growing Guide National planting guide with all states California Planting Calendar All plants for California Onions in Alabama Alabama planting dates Onions in Alaska Alaska planting dates Onions in Arizona Arizona planting dates Onions in Arkansas Arkansas planting dates
Note: All dates are based on NOAA 30-year Climate Normals and represent historical averages, not predictions for any specific year. Always check your local weather forecast before planting frost-sensitive crops. Learn about our data sources.

Last reviewed: March 29, 2026

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