Three Forks, MT 59760 Frost Dates
When can you plant in Three Forks, MT?
Typically, the last spring freeze lands around 05/26, roughly 271 days out. The first fall frost typically arrives around 09/15, about 111 frost-free days later.
Three Forks 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.
What to do before the first frost
About 3 weeks of growing season left in Three Forks before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
Why 05/26 isn't a guarantee
05/26 is the middle of 30 years of NOAA records, not a promise. Plant by 05/11 and you're betting against frost in roughly 9 years out of 10. 06/12 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Three Forks compares
Three Forks's growing season runs about 111 days, ranking 39,463 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 272 of 392.
Learn more
local microclimates covers what one yard in Three Forks can differ from the 59760 normal. zone vs. frost date covers why Zone 5a and Three Forks's frost date answer different questions.