Boulder, CO 80303 Frost Dates
Boulder, CO: when does the frost end?
Around 05/06 is the usual last spring frost, about 251 days away. Fall's first freeze usually shows up around 10/05, roughly 151 days after the last spring frost.
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.
Stretching the season past the first frost
With roughly 5 weeks until Boulder's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
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
At roughly 151 frost-free days, Boulder places 34,934 of 40,283 ZIP codes in this dataset. Within CO, it ranks 304 of 624.
Learn more
Before leaning on 80303's figures: local microclimates explains what one yard in Boulder can differ from the 80303 normal, while zone vs. frost date explains why Zone 6a and Boulder's frost date answer different questions.