St. Marys, IA 50241 Frost Dates
When can you plant in St. Marys, IA?
Around 04/24 is the usual last spring frost, about 239 days away. The first fall frost typically arrives around 10/12, about 168 frost-free days later.
The USDA Plant Hardiness Zone Map puts St. Marys 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
About 6 weeks of growing season left in St. Marys before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
Why 04/24 isn't a guarantee
04/24 is the middle of 30 years of NOAA records, not a promise. Plant by 04/11 and you're betting against frost in roughly 9 years out of 10. 05/08 is the safer bet, historically only a 1-in-10 chance of frost that late.
How St. Marys compares
About 168 days separate St. Marys's last and first frost, putting it 29,808 of 40,283 ZIP codes nationally. Within IA, it ranks 403 of 1,042.
Learn more
zone vs. frost date covers why Zone 5b and St. Marys's frost date answer different questions. the frost range covers how to read the range around St. Marys's dates instead of trusting one.