Casper, WY Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Casper, Wyoming.
Gardening in Casper
Central Wyoming's second city sits on the North Platte River at the base of Casper Mountain. The river provides water; the mountain provides shelter from the worst wind. Together they create a workable garden environment in challenging country.
At 5,100 feet on the Wyoming prairie, Casper's 121-day growing season is one of the shortest in the lower 48. Wind, altitude, and temperature extremes define the challenge. But the North Platte River valley provides fertile soil and irrigation water. Windbreaks and cold frames extend what's possible.
Wyoming self-reliance culture means Casper gardeners don't complain about conditions — they adapt. The Natrona County Master Gardeners are an invaluable resource for navigating High Plains growing challenges.
What This Means for Casper Gardeners
The average last spring frost in Casper is around May 20, and the average first fall frost arrives around September 18. That gives you approximately 121 frost-free days to work with.
121 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 Casper 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 Casper
With 121 frost-free days, Casper 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 Wyoming planting guide for all 40 plants: Wyoming Planting Calendar. Or enter your zip code for exact planting dates personalized to Casper.
More About Zone 5A
Casper 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 Wyoming: Wyoming Planting Calendar.
Other Cities in Wyoming
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Casper 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 Casper (urban heat islands, hilltops, low-lying valleys) can also shift your local frost dates by a week or more.
Start everything possible indoors — your 121-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 20). Choose short-season varieties for warm crops. Enter your zip code for exact dates.