Opheim, MT 59250 Frost Dates
When can you plant in Opheim, MT?
Around 06/01 is the usual last spring frost, about 277 days away. The first fall frost typically arrives around 09/07, about 99 frost-free days later.
Zone 3b (-35 to -30°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 Opheim, not a forecast for this year.
What to do before the first frost
About 1 week of growing season left in Opheim before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
Why 06/01 isn't a guarantee
06/01 is the middle of 30 years of NOAA records, not a promise. Plant by 05/20 and you're betting against frost in roughly 9 years out of 10. 06/18 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Opheim compares
Opheim's growing season runs about 99 days, ranking 39,743 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 316 of 392.
Learn more
zone vs. frost date covers why Zone 3b and Opheim's frost date answer different questions. the frost range covers how to read the range around Opheim's dates instead of trusting one.