Boulder, CO 80301 Frost Dates
80301, near Boulder, CO: the frost window
The last spring frost here typically falls around 05/06, about 251 days from today. Fall's first freeze usually shows up around 10/05, roughly 151 days after the last spring frost.
Boulder sits in USDA Zone 6a (-10 to -5°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
Boulder's growing season runs out in roughly 5 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
The actual range around Boulder's last frost
05/06 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/24 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/18 and only about 1 year in 10 sees frost after that.
Boulder against the rest of the dataset
About 151 days separate Boulder's last and first frost, putting it 34,932 of 40,283 ZIP codes nationally. Within CO, it ranks 302 of 624.
Learn more
Two guides worth reading on 80301: the frost range, on how to read the range around Boulder's dates instead of trusting one, and local microclimates, on what one yard in Boulder can differ from the 80301 normal.