Helena, MT 59640 Frost Dates
When can you plant in Helena, MT?
Typically, the last spring freeze lands around 06/04, roughly 280 days out. The first fall frost typically arrives around 09/14, about 100 frost-free days later.
Helena sits in USDA Zone 4b (-25 to -20°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 2 weeks of growing season left in Helena before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Helena's last frost
06/04 is the middle of 30 years of NOAA records, not a promise. Plant by 05/18 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 Helena compares
At roughly 100 frost-free days, Helena places 39,704 of 40,283 ZIP codes in this dataset. Within MT, it ranks 305 of 392.
Learn more
zone vs. frost date covers why Zone 4b and Helena's frost date answer different questions. the frost range covers how to read the range around Helena's dates instead of trusting one.