Boulder, MT 59632 Frost Dates
Boulder, MT: when does the frost end?
Typically, the last spring freeze lands around 06/07, roughly 283 days out. Fall's first freeze usually shows up around 09/08, roughly 90 days after the last spring frost.
Boulder sits in USDA Zone 5a (-20 to -15°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
With roughly 2 weeks until Boulder's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 06/07 isn't a guarantee
06/07 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/24 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/25 and only about 1 year in 10 sees frost after that.
Boulder against the rest of the dataset
About 90 days separate Boulder's last and first frost, putting it 39,915 of 40,283 ZIP codes nationally. Within MT, it ranks 338 of 392.
Learn more
Before leaning on 59632's figures: the frost range explains how to read the range around Boulder's dates instead of trusting one, while local microclimates explains what one yard in Boulder can differ from the 59632 normal.