Montana · zones 4a–5b
When to plant basil in Montana.
Sow or transplant between Jun 5 to Jul 31 in a typical year, keyed to Montana's median last frost around May 15. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Basil dates for a typical Montana season.
1 · Start indoors
Apr 24 to Jun 19
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Jun 5 to Jul 31
Keyed to the ~May 15 last frost. Sow 0.25" deep, 8" apart.
Harvest
~40 days later
~0.5 lb per plant over ~12 weeks.
Montana spans more than one climate: Zone 4 is the most common zone, but the state runs 4a to 5b. 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 Montana: watch for
The pests that find basil here.
The short season here, about 131 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: Montana gives basil about 131 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 Montana: questions
When should I plant basil in Montana?+
In a typical Montana year, sow basil or set out transplants between Jun 5 to Jul 31, keyed to the state's median last frost around May 15. Your exact dates shift with your ZIP code and microclimate.
When do I start basil seeds indoors in Montana?+
Start seeds inside about 6 weeks before set-out: roughly Apr 24 to Jun 19 for a typical Montana season.
What USDA zone is Montana?+
Montana spans zones 4a–5b, mostly zone 4. 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.