St. Ignatius, MT 59806 Frost Dates
St. Ignatius, MT: when does the frost end?
Typically, the last spring freeze lands around 05/06, roughly 251 days out. Fall's first freeze usually shows up around 10/04, roughly 151 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts St. Ignatius in Zone 5b (-15 to -10°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
With roughly 5 weeks until St. Ignatius's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/06 isn't a guarantee
05/06 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/24 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/19 and only about 1 year in 10 sees frost after that.
St. Ignatius against the rest of the dataset
About 151 days separate St. Ignatius's last and first frost, putting it 35,106 of 40,283 ZIP codes nationally. Within MT, it ranks 16 of 392.
Learn more
Before leaning on 59806's figures: zone vs. frost date explains why Zone 5b and St. Ignatius's frost date answer different questions, while the frost range explains how to read the range around St. Ignatius's dates instead of trusting one.