Montana · zones 4a–5b
When to plant broccoli in Montana.
Sow or transplant between Mar 24 to Apr 21 in a typical year, keyed to Montana's median last frost around May 15. A second, fall sowing fits Jun 9 to Jul 19. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Broccoli dates for a typical Montana season.
1 · Start indoors
Feb 10 to Mar 10
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Mar 24 to Apr 21
Keyed to the ~May 15 last frost. Sow 0.5" deep, 18" apart.
Fall round
Jun 9 to Jul 19
Counted back from the ~Sep 23 first frost.
Harvest
~60 days later
~1.2 lb per plant over ~3 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.