Idaho Falls, ID Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Idaho Falls, Idaho.
Gardening in Idaho Falls
The Gateway to Yellowstone sits on the Snake River Plain at 4,700 feet — high-altitude gardening with volcanic soil and mountain water.
Zone 5a with only 128 frost-free days. The Snake River provides irrigation. Volcanic soil is naturally well-drained but may lack organic matter. Intense sun and cool nights produce exceptional flavor.
Eastern Idaho's agricultural heritage — potatoes, obviously — extends to home gardens that grow exceptional root crops in volcanic soil.
What This Means for Idaho Falls Gardeners
The average last spring frost in Idaho 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 Idaho 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 Idaho Falls
With 128 frost-free days, Idaho 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 Idaho planting guide for all 40 plants: Idaho Planting Calendar. Or enter your zip code for exact planting dates personalized to Idaho Falls.
More About Zone 5A
Idaho Falls is in USDA Hardiness Zone 5A, which means average annual extreme minimum temperatures between -20°F to -15°F. View the full Zone 5A planting guide.
See the complete planting calendar for Idaho: Idaho Planting Calendar.
Other Cities in Idaho
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Idaho 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 Idaho 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.