Shelby, MT 59435 Frost Dates
When can you plant in Shelby, MT?
Typically, the last spring freeze lands around 05/23, roughly 268 days out. The first fall frost typically arrives around 09/16, about 115 frost-free days later.
Shelby sits in USDA Zone 4a (-30 to -25°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 Shelby before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
Why 05/23 isn't a guarantee
05/23 is the middle of 30 years of NOAA records, not a promise. Plant by 05/11 and you're betting against frost in roughly 9 years out of 10. 06/06 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Shelby compares
About 115 days separate Shelby's last and first frost, putting it 39,311 of 40,283 ZIP codes nationally. Within MT, it ranks 243 of 392.
Learn more
local microclimates covers what one yard in Shelby can differ from the 59435 normal. zone vs. frost date covers why Zone 4a and Shelby's frost date answer different questions.