Darby, MT 59835 Frost Dates
Darby, MT: when does the frost end?
Around 05/24 is the usual last spring frost, about 269 days away. Fall's first freeze usually shows up around 09/23, roughly 118 days after the last spring frost.
Zone 5b (-15 to -10°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Darby, not a forecast for this year.
Stretching the season past the first frost
With roughly 4 weeks until Darby's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/24 isn't a guarantee
05/24 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/06 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/14 and only about 1 year in 10 sees frost after that.
Darby against the rest of the dataset
Darby's growing season runs about 118 days, ranking 39,218 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 232 of 392.
Learn more
Before leaning on 59835's figures: zone vs. frost date explains why Zone 5b and Darby's frost date answer different questions, while the frost range explains how to read the range around Darby's dates instead of trusting one.