Colstrip, MT 59012 Frost Dates
Frost dates for Colstrip, MT, ZIP 59012
Typically, the last spring freeze lands around 05/23, roughly 268 days out. The first fall frost typically arrives around 09/15, about 113 frost-free days later.
The USDA Plant Hardiness Zone Map puts Colstrip in Zone 4b (-25 to -20°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 4b around Colstrip has about 3 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
Why 05/23 isn't a guarantee
05/23 is the middle of 30 years of NOAA records, not a promise. Plant by 05/12 and you're betting against frost in roughly 9 years out of 10. 06/07 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Colstrip compares
Colstrip's growing season runs about 113 days, ranking 39,392 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 257 of 392.
Learn more
the frost range explains how to read the range around Colstrip's dates instead of trusting one, and local microclimates explains what one yard in Colstrip can differ from the 59012 normal.