Colstrip, MT 59043 Frost Dates
When can you plant in Colstrip, MT?
Around 05/23 is the usual last spring frost, about 268 days away. The first fall frost typically arrives around 09/15, about 113 frost-free days later.
Colstrip 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 Colstrip before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Colstrip's last frost
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
About 113 days separate Colstrip's last and first frost, putting it 39,393 of 40,283 ZIP codes nationally. Within MT, it ranks 258 of 392.
Learn more
local microclimates covers what one yard in Colstrip can differ from the 59043 normal. zone vs. frost date covers why Zone 5a and Colstrip's frost date answer different questions.