Grinnell, IA 50112 Frost Dates
Frost dates for Grinnell, IA, ZIP 50112
Around 05/03 is the usual last spring frost, about 248 days away. The first fall frost typically arrives around 10/06, about 155 frost-free days later.
The USDA Plant Hardiness Zone Map puts Grinnell in Zone 5b (-15 to -10°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 5b around Grinnell has about 6 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
05/03 is the middle of 30 years of NOAA records, not a promise. Plant by 04/19 and you're betting against frost in roughly 9 years out of 10. 05/17 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Grinnell compares
At roughly 155 frost-free days, Grinnell places 33,940 of 40,283 ZIP codes in this dataset. Within IA, it ranks 867 of 1,042.
Learn more
zone vs. frost date explains why Zone 5b and Grinnell's frost date answer different questions, and the frost range explains how to read the range around Grinnell's dates instead of trusting one.