Growing Cosmos in Zone 10b
Zone 10b has a year-round growing season. Cosmos can be planted almost any time with proper planning. Last frost: Jan 28. First frost: Dec 22.
Planting Calendar
Season: Jan 28 – Dec 22 (328 days)
When to Plant Cosmos in Zone 10b
Start Seeds Indoors: Dec 31
Start Cosmos seeds indoors around Dec 31 (4 weeks before last frost). Optimal germination temperature: 75°F. Germinates in 5–10 days.
Transplant Outdoors: Feb 4
Transplant Cosmos seedlings outdoors after Feb 4. Wait until soil temperature reaches 60°F. Space plants at 12/sqft. Harden off plants for a week before moving outside.
Harvest: Mar 31
First harvest approximately Mar 31 (~55 days from transplant). Continue harvesting until first frost (Dec 22).
Cosmos in Other Zones
1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b 11a 11b 12a 12b 13a 13bFrequently Asked Questions
When should I plant Cosmos in Zone 10b?
Start Cosmos seeds indoors around Dec 31. Transplant outdoors after Feb 4. Expect first harvest around Mar 31.
What is the last frost date for Zone 10b?
The average last spring frost date for Zone 10b is Jan 28. The first fall frost averages Dec 22, giving a 328-day growing season.
Can I grow Cosmos in Zone 10b?
Yes. Cosmos needs 55 days to harvest. Zone 10b has a 328-day growing season, which is sufficient.
What is the best month to plant Cosmos in Zone 10b?
The best time to start Cosmos in Zone 10b is Dec. Begin seeds indoors around Dec 31, then transplant outdoors after the last frost date of Jan 28.
How long does Cosmos take to harvest?
Cosmos takes approximately 55 days from planting to harvest. In Zone 10b, expect your first harvest around Mar 31.
Plan Your Cosmos Garden
Track Cosmos from seed to harvest with personalized frost dates, watering recommendations, and companion planting visualization.
Start Free Cosmos Growing Guide