Bertha, MN 56437 Frost Dates
Frost dates for Bertha, MN, ZIP 56437
Typically, the last spring freeze lands around 05/10, roughly 255 days out. The first fall frost typically arrives around 09/30, about 141 frost-free days later.
The USDA Plant Hardiness Zone Map puts Bertha in Zone 4a (-30 to -25°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 4a around Bertha 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.
The actual range around Bertha's last frost
05/10 is the middle of 30 years of NOAA records, not a promise. Plant by 04/29 and you're betting against frost in roughly 9 years out of 10. 05/25 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Bertha compares
At roughly 141 frost-free days, Bertha places 36,961 of 40,283 ZIP codes in this dataset. Within MN, it ranks 724 of 943.
Learn more
zone vs. frost date explains why Zone 4a and Bertha's frost date answer different questions, and the frost range explains how to read the range around Bertha's dates instead of trusting one.