Portsmouth, IA 51565 Frost Dates
51565, near Portsmouth, 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.
Portsmouth 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
Portsmouth'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.
The actual range around Portsmouth's last frost
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.
Portsmouth against the rest of the dataset
At roughly 165 frost-free days, Portsmouth places 30,759 of 40,283 ZIP codes in this dataset. Within IA, it ranks 555 of 1,042.
Learn more
Two guides worth reading on 51565: zone vs. frost date, on why Zone 5b and Portsmouth's frost date answer different questions, and the frost range, on how to read the range around Portsmouth's dates instead of trusting one.