Missoula, MT Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Missoula, Montana.
Gardening in Missoula
Five valleys converge on Missoula, creating a mountain-sheltered pocket where University of Montana academics, outdoor athletes, and back-to-the-landers share garden fences and growing tips.
Missoula's valley location traps warm air but also cold air — winter inversions can keep the valley foggy and cold while the mountains bask in sun above. Your 138-day growing season is tight. The valley bottom soil is fertile but variable — test before you plant. Wildfire smoke in August has become a growing concern that affects both gardeners and gardens.
The Clark Fork River runs through a city that takes its food heritage seriously. The Missoula Farmers Market is a community gathering as much as a commercial enterprise. UM's environmental studies programs produce graduates who don't just garden — they document, analyze, and optimize.
What This Means for Missoula Gardeners
The average last spring frost in Missoula is around May 10, and the average first fall frost arrives around September 25. That gives you approximately 138 frost-free days to work with.
138 frost-free days means every warm day counts. Focus on cold-hardy crops that thrive in your moderate temperatures: kale, lettuce, peas, radishes, potatoes, and root vegetables. For warm-season crops, choose only the shortest-season varieties (sub-65-day tomatoes, 55-day beans) and start everything indoors. Season extension — row covers, cold frames, plastic mulch — isn't a luxury here, it's essential infrastructure.
These dates are based on NOAA 30-year Climate Normal data for the Missoula area. Your actual frost dates could shift 2-3 weeks in either direction in any given year. Learn more about our data sources.
What to Grow in Missoula
With 138 frost-free days, Missoula gardeners need to plan strategically — start warm-season crops indoors and choose short-season varieties. Cool-season crops are your strength, thriving in the moderate temperatures that define your growing window. Recommended starting points: kale, lettuce, peas, carrots, potatoes, radishes, garlic, and short-season tomatoes.
See the full Montana planting guide for all 40 plants: Montana Planting Calendar. Or enter your zip code for exact planting dates personalized to Missoula.
More About Zone 5B
Missoula is in USDA Hardiness Zone 5B, which means average annual extreme minimum temperatures between -15°F to -10°F. View the full Zone 5B planting guide.
See the complete planting calendar for Montana: Montana Planting Calendar.
Other Cities in Montana
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Missoula area. They represent historical averages, not predictions. In any given year, the actual last frost could be 2-3 weeks earlier or later. Microclimates within Missoula (urban heat islands, hilltops, low-lying valleys) can also shift your local frost dates by a week or more.
Start everything possible indoors — your 138-day season doesn't leave room for a slow start. Direct sow only the fastest, hardiest crops (radishes, lettuce, peas) 3-4 weeks before last frost (May 10). Choose short-season varieties for warm crops. Enter your zip code for exact dates.