St. Ignatius, MT 59865 Frost Dates
Frost dates for St. Ignatius, MT, ZIP 59865
Typically, the last spring freeze lands around 05/12, roughly 257 days out. The first fall frost typically arrives around 10/02, about 142 frost-free days later.
The USDA Plant Hardiness Zone Map puts St. Ignatius in Zone 6a (-10 to -5°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 6a around St. Ignatius 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 St. Ignatius's last frost
05/12 is the middle of 30 years of NOAA records, not a promise. Plant by 04/28 and you're betting against frost in roughly 9 years out of 10. 06/01 is the safer bet, historically only a 1-in-10 chance of frost that late.
How St. Ignatius compares
About 142 days separate St. Ignatius's last and first frost, putting it 36,776 of 40,283 ZIP codes nationally. Within MT, it ranks 59 of 392.
Learn more
zone vs. frost date explains why Zone 6a and St. Ignatius's frost date answer different questions, and the frost range explains how to read the range around St. Ignatius's dates instead of trusting one.