Napoleon, ND 58549 Frost Dates
58549, near Napoleon, ND: the frost window
Around 05/13 is the usual last spring frost, about 258 days away. Fall's first freeze usually shows up around 09/28, roughly 136 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Napoleon 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
Napoleon's growing season runs out in roughly 4 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/13 isn't a guarantee
05/13 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/01 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/26 and only about 1 year in 10 sees frost after that.
Napoleon against the rest of the dataset
At roughly 136 frost-free days, Napoleon places 37,739 of 40,283 ZIP codes in this dataset. Within ND, it ranks 229 of 405.
Learn more
Two guides worth reading on 58549: zone vs. frost date, on why Zone 4a and Napoleon's frost date answer different questions, and the frost range, on how to read the range around Napoleon's dates instead of trusting one.