Colorado · zones 5a–7a
When to plant basil in Colorado.
Sow or transplant between May 30 to Aug 6 in a typical year, keyed to Colorado's median last frost around May 9. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Basil dates for a typical Colorado season.
1 · Start indoors
Apr 18 to Jun 25
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
May 30 to Aug 6
Keyed to the ~May 9 last frost. Sow 0.25" deep, 8" apart.
Harvest
~40 days later
~0.5 lb per plant over ~12 weeks.
Colorado spans more than one climate: Zone 6 is the most common zone, but the state runs 5a to 7a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
In Colorado: watch for
The pests that find basil here.
The short season here, about 143 frost-free days, keeps basil in front of aphids only briefly. One early row cover usually carries a planting through the worst of it.
Fine webbing and pale stippling in hot, dry spells.
Organic fix: Spray the undersides with water, then insecticidal soap or neem.
Yellowing with gray fuzz underneath, or white powder on top.
Organic fix: Space for airflow, water at the base, spray neem.
Metallic beetles chewing basil and mint leaves to lace.
Organic fix: Handpick into soapy water in the morning; neem.
Your season math: Colorado gives basil about 143 frost-free days, and it needs roughly 40 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting basil in Colorado: questions
When should I plant basil in Colorado?+
In a typical Colorado year, sow basil or set out transplants between May 30 to Aug 6, keyed to the state's median last frost around May 9. Your exact dates shift with your ZIP code and microclimate.
When do I start basil seeds indoors in Colorado?+
Start seeds inside about 6 weeks before set-out: roughly Apr 18 to Jun 25 for a typical Colorado season.
What USDA zone is Colorado?+
Colorado spans zones 5a–7a, mostly zone 6. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many basil plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.