Flagstaff, AZ Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Flagstaff, Arizona.
Gardening in Flagstaff
At 7,000 feet in the ponderosa pines, Flagstaff is Arizona's mountain city — a world apart from the desert below. Gardening here is more like Colorado than Phoenix, with cold winters and short summers.
Zone 5b at Arizona altitude creates conditions that would baffle gardeners from Tucson or Phoenix. Your 113-day growing season is the shortest in Arizona. Snow is measured in feet, not inches. But the volcanic soil from the San Francisco Peaks is naturally fertile, and the cool mountain air grows exceptional cool-season crops.
NAU's campus gardens and the Flagstaff Community Gardens prove that mountain desert gardening works. The weekend farmers market draws from the surrounding high-country farms and gardens. Flagstaff gardeners share more growing tips with Denver than with Phoenix.
What This Means for Flagstaff Gardeners
The average last spring frost in Flagstaff is around May 25, and the average first fall frost arrives around September 15. That gives you approximately 113 frost-free days to work with.
113 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 Flagstaff 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 Flagstaff
With 113 frost-free days, Flagstaff 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 Arizona planting guide for all 40 plants: Arizona Planting Calendar. Or enter your zip code for exact planting dates personalized to Flagstaff.
More About Zone 5B
Flagstaff 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 Arizona: Arizona Planting Calendar.
Other Cities in Arizona
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Flagstaff 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 Flagstaff (urban heat islands, hilltops, low-lying valleys) can also shift your local frost dates by a week or more.
Start everything possible indoors — your 113-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 25). Choose short-season varieties for warm crops. Enter your zip code for exact dates.