Hamilton, MT 59828 Frost Dates
Hamilton, MT: when does the frost end?
Typically, the last spring freeze lands around 05/23, roughly 268 days out. Fall's first freeze usually shows up around 09/21, roughly 118 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Hamilton 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 3 weeks until Hamilton's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/23 isn't a guarantee
05/23 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/08 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/10 and only about 1 year in 10 sees frost after that.
Hamilton against the rest of the dataset
About 118 days separate Hamilton's last and first frost, putting it 39,199 of 40,283 ZIP codes nationally. Within MT, it ranks 228 of 392.
Learn more
Before leaning on 59828's figures: the frost range explains how to read the range around Hamilton's dates instead of trusting one, while local microclimates explains what one yard in Hamilton can differ from the 59828 normal.