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.
In Montana: watch for
The pests that find broccoli here.
The short season here, about 131 frost-free days, keeps broccoli in front of cabbage worms & loopers only briefly. One early row cover usually carries a planting through the worst of it.
Green caterpillars chewing ragged holes; green droppings.
Organic fix: Handpick, cover with netting, spray Bt.
Gray-green clusters tucked into the leaf folds.
Organic fix: Blast with water, then insecticidal soap.
Tiny holes peppering the young leaves.
Organic fix: Row cover from day one; diatomaceous earth.
Black rot
Yellow V-shaped wedges cutting in from the leaf edge, veins blackening inside.
Organic fix: Pull infected plants, water at the base, keep brassicas out of that bed 3 years.
Seedlings wilt, yellow and stall for no reason; white maggots tunnel the roots.
Organic fix: Row cover before the flies are up, when yellow rocket blooms; rotate the bed.
Your season math: Montana gives broccoli about 131 frost-free days, and it needs roughly 60 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting broccoli in Montana: questions
When should I plant broccoli in Montana?+
In a typical Montana year, sow broccoli or set out transplants between Mar 24 to Apr 21, keyed to the state's median last frost around May 15. There's also a fall window: Jun 9 to Jul 19. Your exact dates shift with your ZIP code and microclimate.
When do I start broccoli seeds indoors in Montana?+
Start seeds inside about 6 weeks before set-out: roughly Feb 10 to Mar 10 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 broccoli 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.