Polson, MT 59931 Frost Dates
59931, near Polson, MT: the frost window
Around 05/01 is the usual last spring frost, about 246 days away. Fall's first freeze usually shows up around 10/15, roughly 165 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Polson 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
Polson's growing season runs out in roughly 7 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/01 isn't a guarantee
05/01 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/16 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/16 and only about 1 year in 10 sees frost after that.
Polson against the rest of the dataset
Polson's growing season runs about 165 days, ranking 30,537 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 5 of 392.
Learn more
Two guides worth reading on 59931: the frost range, on how to read the range around Polson's dates instead of trusting one, and local microclimates, on what one yard in Polson can differ from the 59931 normal.