Fort Benton, MT 59442 Frost Dates
59442, near Fort Benton, MT: the frost window
Around 05/15 is the usual last spring frost, about 260 days away. Fall's first freeze usually shows up around 09/22, roughly 129 days after the last spring frost.
Fort Benton sits in USDA Zone 4a (-30 to -25°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
Fort Benton's growing season runs out in roughly 4 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 Fort Benton's last frost
05/15 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/03 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/30 and only about 1 year in 10 sees frost after that.
Fort Benton against the rest of the dataset
Fort Benton's growing season runs about 129 days, ranking 38,471 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 136 of 392.
Learn more
Two guides worth reading on 59442: the frost range, on how to read the range around Fort Benton's dates instead of trusting one, and local microclimates, on what one yard in Fort Benton can differ from the 59442 normal.