Bismarck, ND 58505 Frost Dates
Bismarck, ND: when does the frost end?
Typically, the last spring freeze lands around 05/10, roughly 255 days out. Fall's first freeze usually shows up around 09/30, roughly 142 days after the last spring frost.
Bismarck sits in USDA Zone 4a (-30 to -25°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
With roughly 5 weeks until Bismarck's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/10 isn't a guarantee
05/10 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/30 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/23 and only about 1 year in 10 sees frost after that.
Bismarck against the rest of the dataset
About 142 days separate Bismarck's last and first frost, putting it 36,702 of 40,283 ZIP codes nationally. Within ND, it ranks 107 of 405.
Learn more
Before leaning on 58505's figures: zone vs. frost date explains why Zone 4a and Bismarck's frost date answer different questions, while the frost range explains how to read the range around Bismarck's dates instead of trusting one.