Forsyth, MT 59347 Frost Dates
When can you plant in Forsyth, MT?
Around 05/15 is the usual last spring frost, about 260 days away. The first fall frost typically arrives around 09/25, about 132 frost-free days later.
The USDA Plant Hardiness Zone Map puts Forsyth 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
About 4 weeks of growing season left in Forsyth before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
How much risk comes with planting early here
05/15 is the middle of 30 years of NOAA records, not a promise. Plant by 05/02 and you're betting against frost in roughly 9 years out of 10. 05/27 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Forsyth compares
About 132 days separate Forsyth's last and first frost, putting it 38,204 of 40,283 ZIP codes nationally. Within MT, it ranks 122 of 392.
Learn more
zone vs. frost date covers why Zone 4b and Forsyth's frost date answer different questions. the frost range covers how to read the range around Forsyth's dates instead of trusting one.