Montana · zones 4a–5b
When to plant spinach in Montana.
Sow between Mar 24 to May 5 in a typical year, keyed to Montana's median last frost around May 15. A second, fall sowing fits Jul 10 to Aug 28. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Spinach dates for a typical Montana season.
Direct sow
Mar 24 to May 5
Keyed to the ~May 15 last frost. Sow 0.5" deep, 3" apart.
Fall round
Jul 10 to Aug 28
Counted back from the ~Sep 23 first frost.
Harvest
~42 days later
~0.25 lb per plant over ~1 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 spinach here.
The short season here, about 131 frost-free days, keeps spinach in front of leaf miners only briefly. One early row cover usually carries a planting through the worst of it.
Winding pale tunnels or blotches inside the leaves.
Organic fix: Pick and destroy mined leaves; cover the row.
Cercospora leaf spot
Round spots with gray centers and a red-purple rim, oldest leaves worst.
Organic fix: Space wider so leaves dry fast, clear old debris, and pull pigweed and lambsquarters nearby.
Your season math: Montana gives spinach about 131 frost-free days, and it needs roughly 42 days to a first harvest. That fits about 13 re-sown rounds across the season, so you can keep it coming instead of picking once.
Planting spinach in Montana: questions
When should I plant spinach in Montana?+
In a typical Montana year, sow spinach between Mar 24 to May 5, keyed to the state's median last frost around May 15. There's also a fall window: Jul 10 to Aug 28. Your exact dates shift with your ZIP code and microclimate.
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 spinach 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.