Great Falls, MT 59440 Frost Dates
Great Falls, MT: when does the frost end?
The last spring frost here typically falls around 05/23, about 268 days from today. Fall's first freeze usually shows up around 09/23, roughly 120 days after the last spring frost.
Zone 4b (-25 to -20°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 Great Falls, not a forecast for this year.
Stretching the season past the first frost
With roughly 4 weeks until Great Falls's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
How much risk comes with planting early here
05/23 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/10 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/09 and only about 1 year in 10 sees frost after that.
Great Falls against the rest of the dataset
Great Falls's growing season runs about 120 days, ranking 39,065 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 213 of 392.
Learn more
Before leaning on 59440's figures: local microclimates explains what one yard in Great Falls can differ from the 59440 normal, while zone vs. frost date explains why Zone 4b and Great Falls's frost date answer different questions.