Great Falls, MT Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Great Falls, Montana.
Gardening in Great Falls
The Electric City sits where the Great Falls of the Missouri provided power for the region's development. The river valley creates a fertile corridor through the northern Montana prairie.
Zone 4b with genuine continental climate — winter temperatures below -20°F are routine. Your 128-day growing season demands aggressive indoor starting and short-season varieties. But the Missouri River bottomland is fertile, and the intense northern sun drives rapid growth.
Lewis and Clark portaged around the falls that named this city — Great Falls gardeners share that explorer spirit, pushing the limits of what grows at this latitude and elevation.
What This Means for Great Falls Gardeners
The average last spring frost in Great Falls is around May 15, and the average first fall frost arrives around September 20. That gives you approximately 128 frost-free days to work with.
128 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 Great Falls 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 Great Falls
With 128 frost-free days, Great Falls 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 Great Falls.
More About Zone 4B
Great Falls is in USDA Hardiness Zone 4B, which means average annual extreme minimum temperatures between -25°F to -20°F. View the full Zone 4B 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 Great Falls 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 Great Falls (urban heat islands, hilltops, low-lying valleys) can also shift your local frost dates by a week or more.
Start everything possible indoors — your 128-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 15). Choose short-season varieties for warm crops. Enter your zip code for exact dates.