Boulder, CO 80302 Frost Dates
Frost dates for Boulder, CO, ZIP 80302
Around 05/06 is the usual last spring frost, about 251 days away. The first fall frost typically arrives around 10/05, about 151 frost-free days later.
The USDA Plant Hardiness Zone Map puts Boulder in Zone 6a (-10 to -5°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 6a around Boulder has about 5 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
Why 05/06 isn't a guarantee
05/06 is the middle of 30 years of NOAA records, not a promise. Plant by 04/24 and you're betting against frost in roughly 9 years out of 10. 05/18 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Boulder compares
About 151 days separate Boulder's last and first frost, putting it 34,933 of 40,283 ZIP codes nationally. Within CO, it ranks 303 of 624.
Learn more
zone vs. frost date explains why Zone 6a and Boulder's frost date answer different questions, and the frost range explains how to read the range around Boulder's dates instead of trusting one.