Harlan, IA 51537 Frost Dates
51537, near Harlan, IA: the frost window
Typically, the last spring freeze lands around 04/27, roughly 242 days out. Fall's first freeze usually shows up around 10/09, roughly 165 days after the last spring frost.
Harlan 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
Harlan'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
04/27 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/12 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/09 and only about 1 year in 10 sees frost after that.
Harlan against the rest of the dataset
Harlan's growing season runs about 165 days, ranking 30,540 of 40,283 US ZIP codes measured here, longest to shortest. Within IA, it ranks 493 of 1,042.
Learn more
Two guides worth reading on 51537: local microclimates, on what one yard in Harlan can differ from the 51537 normal, and zone vs. frost date, on why Zone 5b and Harlan's frost date answer different questions.