St. Ignatius, MT 59812 Frost Dates
When can you plant in St. Ignatius, MT?
Around 05/06 is the usual last spring frost, about 251 days away. The first fall frost typically arrives around 10/04, about 151 frost-free days later.
Zone 5b (-15 to -10°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 St. Ignatius, not a forecast for this year.
What to do before the first frost
About 5 weeks of growing season left in St. Ignatius before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
Why 05/06 isn't a guarantee
05/06 is the middle of 30 years of NOAA records, not a promise. Plant by 04/24 and you're betting against frost in roughly 9 years out of 10. 05/19 is the safer bet, historically only a 1-in-10 chance of frost that late.
How St. Ignatius compares
About 151 days separate St. Ignatius's last and first frost, putting it 35,107 of 40,283 ZIP codes nationally. Within MT, it ranks 17 of 392.
Learn more
the frost range covers how to read the range around St. Ignatius's dates instead of trusting one. local microclimates covers what one yard in St. Ignatius can differ from the 59812 normal.