Thor, IA 50591 Frost Dates
50591, near Thor, IA: the frost window
Around 04/26 is the usual last spring frost, about 241 days away. Fall's first freeze usually shows up around 10/12, roughly 169 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Thor in Zone 5a (-20 to -15°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
Thor's growing season runs out in roughly 6 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
04/26 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/11 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/07 and only about 1 year in 10 sees frost after that.
Thor against the rest of the dataset
About 169 days separate Thor's last and first frost, putting it 29,613 of 40,283 ZIP codes nationally. Within IA, it ranks 357 of 1,042.
Learn more
Two guides worth reading on 50591: local microclimates, on what one yard in Thor can differ from the 50591 normal, and zone vs. frost date, on why Zone 5a and Thor's frost date answer different questions.