Polson, MT 59911 Frost Dates
Polson, MT: when does the frost end?
Typically, the last spring freeze lands around 05/01, roughly 246 days out. Fall's first freeze usually shows up around 10/15, roughly 165 days after the last spring frost.
Zone 5b (-15 to -10°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Polson, not a forecast for this year.
Stretching the season past the first frost
With roughly 7 weeks until Polson's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
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 30,534 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 2 of 392.
Learn more
Before leaning on 59911's figures: local microclimates explains what one yard in Polson can differ from the 59911 normal, while zone vs. frost date explains why Zone 5b and Polson's frost date answer different questions.