When is the last frost in Denver, Colorado?

Denver's average last spring frost falls in early-to-mid May, based on NOAA climate normals. This is the median date by which the risk of a 32°F freeze has typically passed, though about half of years see a later frost. On the Front Range, late spring snows and freezes are common, so many Denver gardeners wait well past the average date before planting tender plants.

When is the first frost in Denver, Colorado?

Denver's average first fall frost falls in late September to early October, based on NOAA climate normals. As with the spring date, it is a median: roughly half of years see an earlier first frost and half see a later one, and higher-elevation foothills and western suburbs frost weeks earlier than the lower-elevation eastern metro.

How long is the growing season in Denver?

Denver's average frost-free growing season runs roughly 150 to 160 days, from the early-to-mid-May last frost to the late-September-to-early-October first frost. That is a relatively short season, which is why cool-season grasses and cold-hardy, water-wise plants are the standard on the high-altitude Front Range.

What USDA hardiness zone is Denver, Colorado?

Denver sits in USDA Plant Hardiness Zone 5b to 6a, covering much of the metro. Zone 5b has an average annual minimum of -15°F to -10°F and Zone 6a -10°F to -5°F. Higher-elevation areas trend colder. Use the zone rating to choose plants rated to survive Denver's winter lows.

Do frost dates vary across the Denver area?

Yes, strongly, because of elevation. The urban core and lower-elevation eastern metro run warmest with the latest first frosts, while higher-elevation foothills and western suburbs frost weeks earlier in fall and later in spring, with the growing season shortening fast toward the mountains. Treat your own yard's elevation and microclimate as the final word.

When should I plant grass based on Denver's frost dates?

Denver's cool-season Kentucky bluegrass and fescue plant best in late summer to early fall and in spring, not the heat of summer. Use the late-September-to-early-October first frost to close the fall window in time for roots to establish, and the early-to-mid-May last frost to gate spring planting. Denver is too cold for warm-season lawn grasses like Bermuda.

Denver Frost Dates & Planting Calendar (2026)

Quick answer: In Denver, Colorado, the average last spring frost falls in early-to-mid May and the average first fall frost falls in late September to early October, giving the Front Range a relatively short growing season of roughly 150 to 160 days. Denver sits in USDA Plant Hardiness Zone 5b to 6a (much of the metro is 5b to 6a). Because frost timing varies year to year and across the high-altitude Front Range, these are long-term averages based on NOAA climate normals, your specific yard, and elevation, can run a week or two different. Use them to time cool-season grass planting, protect tender plants, and plan around Denver’s narrow season.

Denver frost dates and growing season at a glance

<table> <thead> <tr> <th>Metric</th> <th>Denver, CO (long-term average)</th> </tr> </thead> <tbody> <tr> <td>Average last spring frost (32°F)</td> <td>Early to mid May</td> </tr> <tr> <td>Average first fall frost (32°F)</td> <td>Late September to early October</td> </tr> <tr> <td>Average frost-free growing season</td> <td>~150–160 days</td> </tr> <tr> <td>USDA Plant Hardiness Zone</td> <td>5b–6a (much of the metro)</td> </tr> <tr> <td>Zone 5b average annual minimum temp</td> <td>-15°F to -10°F</td> </tr> <tr> <td>Zone 6a average annual minimum temp</td> <td>-10°F to -5°F</td> </tr> <tr> <td>Source basis</td> <td>NOAA U.S. Climate Normals; USDA Plant Hardiness Zone Map</td> </tr> </tbody> </table>

What “average frost date” actually means

A frost date is a probability, not a guarantee. The “average last frost” is the date by which, in a typical year, the risk of a 32°F freeze has passed, but roughly half of years see a later frost and half see an earlier one. NOAA publishes these as climate normals at several probability levels (for example, a 10%, 50%, and 90% chance of frost after a given date). The dates above are the 50% (median) values for the Denver area. On the Front Range, late spring snows and freezes are common, so for frost-sensitive plants gardeners often wait until the 10%-risk date, well past the average, to be safe.

Why Denver’s frost dates vary across the Front Range

Denver’s frost timing is strongly tied to elevation and terrain:

The urban core and lower-elevation eastern metro run warmest thanks to the heat-island effect and lower altitude, with the latest first frosts.
Higher-elevation foothills and western suburbs sit colder and can see frost weeks earlier in fall and later in spring, the growing season shortens fast as you climb toward the mountains.
Low spots and open plains cool quickly on clear, calm high-altitude nights and can get localized frost when the city does not.

Because of Denver’s mile-high altitude and semi-arid air, temperatures swing widely day to night, so treat your own yard’s elevation and microclimate as the final word.

What the short growing season means for your Denver lawn and garden

Denver’s 150-to-160-day growing season is short, and it shapes the whole lawn and landscape calendar:

Cool-season grasses rule. Kentucky bluegrass and fescue are timed around the season’s edges, the best planting windows are late summer to early fall and spring, not the heat of summer. Denver is too cold for warm-season lawn grasses like Bermuda.
Frost brackets a narrow window. The early-to-mid-May last frost and late-September-to-early-October first frost leave a compact season, so timing matters more than in milder climates.
Plant cold-hardy and water-wise. Zone 5b-6a plant choices and native, drought-adapted species (and xeriscape) handle both the cold and the semi-arid Front Range climate.
Watch late spring freezes. A warm April can tempt early planting, but a May freeze is common, hold tender plants until the risk passes.

How to use these dates

Use the average last frost (early-to-mid May) to time spring planting of cool-season grass and frost-tender plants, waiting past it on the Front Range where late freezes are common. Use the average first frost (late September to early October) to schedule fall planting (the prime late-summer-to-early-fall grass window closes here), fall cleanup, and tender-plant protection. And use the USDA Zone 5b-6a rating to choose plants rated to survive Denver’s winter lows. For a plan built around your exact lot, elevation, and microclimate, a local pro can dial in the timing.

Talk to a Denver Landscaping Pro

Want a planting and lawn-care calendar built around Denver’s frost dates, short growing season, and your specific yard? Denver Pro Landscape offers free written estimates. Call (720) 650-0165.

Denver Frost Dates & Growing Season: Average First Frost, Last Frost, and Season Length