Shelby, MT 59474 Frost Dates
Shelby, MT: when does the frost end?
Around 05/23 is the usual last spring frost, about 268 days away. Fall's first freeze usually shows up around 09/16, roughly 115 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Shelby in Zone 4a (-30 to -25°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
With roughly 3 weeks until Shelby's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
The actual range around Shelby's last frost
05/23 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/11 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/06 and only about 1 year in 10 sees frost after that.
Shelby against the rest of the dataset
At roughly 115 frost-free days, Shelby places 39,313 of 40,283 ZIP codes in this dataset. Within MT, it ranks 245 of 392.
Learn more
Before leaning on 59474's figures: local microclimates explains what one yard in Shelby can differ from the 59474 normal, while zone vs. frost date explains why Zone 4a and Shelby's frost date answer different questions.