Harper, IA 52231 Frost Dates
52231, near Harper, IA: the frost window
Typically, the last spring freeze lands around 04/28, roughly 243 days out. Fall's first freeze usually shows up around 10/09, roughly 164 days after the last spring frost.
Harper sits in USDA Zone 5b (-15 to -10°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
Harper'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
04/28 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/14 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/12 and only about 1 year in 10 sees frost after that.
Harper against the rest of the dataset
At roughly 164 frost-free days, Harper places 31,241 of 40,283 ZIP codes in this dataset. Within IA, it ranks 650 of 1,042.
Learn more
Two guides worth reading on 52231: zone vs. frost date, on why Zone 5b and Harper's frost date answer different questions, and the frost range, on how to read the range around Harper's dates instead of trusting one.