Annual Flower

When to Plant Cosmos in California

Delicate, daisy-like blooms that dance in the breeze. Cosmos thrive in poor soil and practically grow themselves.

The Short Answer

Cosmos are a California wildflower garden essential — they thrive in the state's dry conditions and bloom prolifically with minimal water.

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

Cosmos 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
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Central Valley (Zones 9a, 9b)

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

Start Seeds Indoors
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after 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
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Bay Area (Zones 9b, 10a)

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

Start Seeds Indoors
4 wks before frost
Transplant Outside
1 wks after frost
Direct Sow
1 wks after frost

Growing Cosmos in California

State-Specific Growing Tips

Sow from March through May statewide. Poor soil is preferred. Minimal water. Full sun. Self-seeds for following years.

Recommended Varieties for California

Sensation Mix, Bright Lights, Rubenza (dark crimson). All varieties thrive in California.

Common Challenges in California

Essentially trouble-free in California's dry climate.

Growing Tips

Don't over-fertilize — rich soil produces more leaves and fewer flowers. Let some flowers go to seed for next year's crop.

Companion Planting

Plant cosmos alongside these companions for better growth:

Tomatoes Squash

The Bottom Line

Cosmos 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

Cosmos Growing Guide National planting guide with all states California Planting Calendar All plants for California Cosmos in Alabama Alabama planting dates Cosmos in Alaska Alaska planting dates Cosmos in Arizona Arizona planting dates Cosmos 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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