East Helena, MT 59635 Frost Dates
When can you plant in East Helena, MT?
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.
East Helena sits in USDA Zone 5a (-20 to -15°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 5 weeks of growing season left in East Helena before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
How much risk comes with planting early here
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 East Helena compares
About 142 days separate East Helena's last and first frost, putting it 36,746 of 40,283 ZIP codes nationally. Within MT, it ranks 55 of 392.
Learn more
local microclimates covers what one yard in East Helena can differ from the 59635 normal. zone vs. frost date covers why Zone 5a and East Helena's frost date answer different questions.