Coleharbor, ND 58531 Frost Dates
58531, near Coleharbor, ND: the frost window
Typically, the last spring freeze lands around 05/10, roughly 255 days out. Fall's first freeze usually shows up around 09/29, roughly 139 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Coleharbor 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
Coleharbor'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.
How much risk comes with planting early here
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 05/25 and only about 1 year in 10 sees frost after that.
Coleharbor against the rest of the dataset
About 139 days separate Coleharbor's last and first frost, putting it 37,315 of 40,283 ZIP codes nationally. Within ND, it ranks 166 of 405.
Learn more
Two guides worth reading on 58531: zone vs. frost date, on why Zone 4a and Coleharbor's frost date answer different questions, and the frost range, on how to read the range around Coleharbor's dates instead of trusting one.