Denver, CO Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Denver, Colorado.
Gardening in Denver
Denver gardening is a high-altitude adventure. At 5,280 feet, the sun is more intense, the air is thinner and drier, and a sunny 70°F day can turn into a snowstorm overnight. Colorado gardeners learn to roll with the punches — and to never put tomatoes out before Memorial Day, no matter how warm April feels.
The altitude changes everything. Intense UV means faster sunburn (for you and your lettuce). Low humidity means less disease but more watering. The notorious Colorado hailstorms can shred a garden in minutes — many Denver gardeners keep row cover on hand like an emergency blanket. The 300+ days of sunshine are genuine, but so are the 60-degree temperature swings in a single day.
Broncos fans understand dramatic reversals of fortune, which is excellent preparation for Front Range gardening. One week you're harvesting lettuce in shirtsleeves, the next week there's 8 inches of snow on your raised beds. The snow melts by Thursday. It's fine. Denver's craft beer scene has spawned a parallel hop-growing hobby scene — backyard hop vines climbing garage walls across the city.
What This Means for Denver Gardeners
The average last spring frost in Denver is around May 1, and the average first fall frost arrives around October 5. That gives you approximately 157 frost-free days to work with.
At 157 days, you're working with a compressed but productive window. Choose varieties by their days-to-maturity number — anything under 75 days is safe, 75-90 requires indoor starting, and 90+ is a calculated risk. The tradeoff: your cool, moderate summers are excellent for crops that heat-zone gardeners struggle with. Your lettuce doesn't bolt in June. Your peas produce for weeks longer. Cool-season crops are your superpower.
These dates are based on NOAA 30-year Climate Normal data for the Denver 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 Denver
Denver's 157-day season gives you plenty of time for most vegetables with good planning. Start warm-season crops indoors to maximize your window. Cool-season crops thrive in your spring and fall shoulder seasons. Recommended starting points: tomatoes, peppers, lettuce, carrots, beans, broccoli, garlic, and basil.
See the full Colorado planting guide for all 40 plants: Colorado Planting Calendar. Or enter your zip code for exact planting dates personalized to Denver.
More About Zone 5B
Denver 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 Colorado: Colorado Planting Calendar.
Other Cities in Colorado
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Denver 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 Denver (urban heat islands, hilltops, low-lying valleys) can also shift your local frost dates by a week or more.
Start warm-season seeds indoors 6-8 weeks before your last frost (May 1) to maximize your 157-day window. Direct sow cold-hardy crops like peas and lettuce 3-4 weeks before last frost. Every week of early indoor starting matters at this season length. Enter your zip code for exact dates.