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.