Bismarck, ND 58503 Frost Dates
58503, near Bismarck, ND: the frost window
Around 05/10 is the usual last spring frost, about 255 days away. Fall's first freeze usually shows up around 09/30, roughly 142 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Bismarck in Zone 4a (-30 to -25°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
Bismarck's growing season runs out in roughly 5 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
The actual range around Bismarck's last frost
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
Bismarck's growing season runs about 142 days, ranking 36,701 of 40,283 US ZIP codes measured here, longest to shortest. Within ND, it ranks 106 of 405.
Learn more
Two guides worth reading on 58503: local microclimates, on what one yard in Bismarck can differ from the 58503 normal, and zone vs. frost date, on why Zone 4a and Bismarck's frost date answer different questions.