Helena, MT 59604 Frost Dates
When can you plant in Helena, MT?
Around 05/09 is the usual last spring frost, about 254 days away. 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
About 5 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
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 36,706 of 40,283 ZIP codes nationally. Within MT, it ranks 50 of 392.
Learn more
the frost range covers how to read the range around Helena's dates instead of trusting one. local microclimates covers what one yard in Helena can differ from the 59604 normal.