Helena, MT 59602 Frost Dates
Frost dates for Helena, MT, ZIP 59602
The last spring frost here typically falls around 05/09, about 254 days from today. The first fall frost typically arrives around 09/30, about 142 frost-free days later.
The USDA Plant Hardiness Zone Map puts Helena in Zone 4b (-25 to -20°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 4b around Helena has about 5 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
The actual range around Helena's last frost
05/09 is the middle of 30 years of NOAA records, not a promise. Plant by 04/29 and you're betting against frost in roughly 9 years out of 10. 05/25 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Helena compares
About 142 days separate Helena's last and first frost, putting it 36,705 of 40,283 ZIP codes nationally. Within MT, it ranks 49 of 392.
Learn more
the frost range explains how to read the range around Helena's dates instead of trusting one, and local microclimates explains what one yard in Helena can differ from the 59602 normal.