Bismarck, ND 58502 Frost Dates
Frost dates for Bismarck, ND, ZIP 58502
The last spring frost here typically falls around 05/10, about 255 days from today. The first fall frost typically arrives around 09/30, about 142 frost-free days later.
Zone 4a (-30 to -25°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 Bismarck, not a forecast for this year.
What to do before the first frost
Zone 4a around Bismarck has about 5 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
How much risk comes with planting early here
05/10 is the middle of 30 years of NOAA records, not a promise. Plant by 04/30 and you're betting against frost in roughly 9 years out of 10. 05/23 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Bismarck compares
About 142 days separate Bismarck's last and first frost, putting it 36,700 of 40,283 ZIP codes nationally. Within ND, it ranks 105 of 405.
Learn more
the frost range explains how to read the range around Bismarck's dates instead of trusting one, and local microclimates explains what one yard in Bismarck can differ from the 58502 normal.