Darby, MT 59829 Frost Dates
When can you plant in Darby, MT?
Around 05/24 is the usual last spring frost, about 269 days away. The first fall frost typically arrives around 09/23, about 118 frost-free days later.
The USDA Plant Hardiness Zone Map puts Darby in Zone 5b (-15 to -10°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 Darby before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Darby's last frost
05/24 is the middle of 30 years of NOAA records, not a promise. Plant by 05/06 and you're betting against frost in roughly 9 years out of 10. 06/14 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Darby compares
Darby's growing season runs about 118 days, ranking 39,217 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 231 of 392.
Learn more
zone vs. frost date covers why Zone 5b and Darby's frost date answer different questions. the frost range covers how to read the range around Darby's dates instead of trusting one.