Growing Cosmos in Zone 6b
Zone 6b has mild winters and a long growing season — good conditions for Cosmos. Last frost: Apr 15. First frost: Oct 22.
Planting Calendar
Season: Apr 15 – Oct 22 (190 days)
When to Plant Cosmos in Zone 6b
Start Seeds Indoors: Mar 18
Start Cosmos seeds indoors around Mar 18 (4 weeks before last frost). Optimal germination temperature: 75°F. Germinates in 5–10 days.
Transplant Outdoors: Apr 22
Transplant Cosmos seedlings outdoors after Apr 22. Wait until soil temperature reaches 60°F. Space plants at 12/sqft. Harden off plants for a week before moving outside.
Harvest: Jun 16
First harvest approximately Jun 16 (~55 days from transplant). Continue harvesting until first frost (Oct 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 6b?
Start Cosmos seeds indoors around Mar 18. Transplant outdoors after Apr 22. Expect first harvest around Jun 16.
What is the last frost date for Zone 6b?
The average last spring frost date for Zone 6b is Apr 15. The first fall frost averages Oct 22, giving a 190-day growing season.
Can I grow Cosmos in Zone 6b?
Yes. Cosmos needs 55 days to harvest. Zone 6b has a 190-day growing season, which is sufficient.
What is the best month to plant Cosmos in Zone 6b?
The best time to start Cosmos in Zone 6b is Mar. Begin seeds indoors around Mar 18, then transplant outdoors after the last frost date of Apr 15.
How long does Cosmos take to harvest?
Cosmos takes approximately 55 days from planting to harvest. In Zone 6b, expect your first harvest around Jun 16.
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