Growing Cosmos in Zone 11b
Zone 11b has a year-round growing season. Cosmos can be planted almost any time with proper planning. Last frost: Jan 15. First frost: Dec 31.
Planting Calendar
Season: Jan 15 – Dec 31 (350 days)
When to Plant Cosmos in Zone 11b
Start Seeds Indoors: Dec 18
Start Cosmos seeds indoors around Dec 18 (4 weeks before last frost). Optimal germination temperature: 75°F. Germinates in 5–10 days.
Transplant Outdoors: Jan 22
Transplant Cosmos seedlings outdoors after Jan 22. Wait until soil temperature reaches 60°F. Space plants at 12/sqft. Harden off plants for a week before moving outside.
Harvest: Mar 18
First harvest approximately Mar 18 (~55 days from transplant). Continue harvesting until first frost (Dec 31).
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 11b?
Start Cosmos seeds indoors around Dec 18. Transplant outdoors after Jan 22. Expect first harvest around Mar 18.
What is the last frost date for Zone 11b?
The average last spring frost date for Zone 11b is Jan 15. The first fall frost averages Dec 31, giving a 350-day growing season.
Can I grow Cosmos in Zone 11b?
Yes. Cosmos needs 55 days to harvest. Zone 11b has a 350-day growing season, which is sufficient.
What is the best month to plant Cosmos in Zone 11b?
The best time to start Cosmos in Zone 11b is Dec. Begin seeds indoors around Dec 18, then transplant outdoors after the last frost date of Jan 15.
How long does Cosmos take to harvest?
Cosmos takes approximately 55 days from planting to harvest. In Zone 11b, expect your first harvest around Mar 18.
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