Plains, MT 59856 Frost Dates
59856, near Plains, MT: the frost window
Typically, the last spring freeze lands around 05/17, roughly 262 days out. Fall's first freeze usually shows up around 09/23, roughly 125 days after the last spring frost.
Plains sits in USDA Zone 6a (-10 to -5°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
Plains'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 Plains's last frost
05/17 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/01 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/08 and only about 1 year in 10 sees frost after that.
Plains against the rest of the dataset
About 125 days separate Plains's last and first frost, putting it 38,768 of 40,283 ZIP codes nationally. Within MT, it ranks 172 of 392.
Learn more
Two guides worth reading on 59856: local microclimates, on what one yard in Plains can differ from the 59856 normal, and zone vs. frost date, on why Zone 6a and Plains's frost date answer different questions.