Hull, IA 51239 Frost Dates
51239, near Hull, IA: the frost window
Typically, the last spring freeze lands around 04/30, roughly 245 days out. Fall's first freeze usually shows up around 10/03, roughly 154 days after the last spring frost.
Zone 5a (-20 to -15°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Hull, not a forecast for this year.
Stretching the season past the first frost
Hull's growing season runs out in roughly 5 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
04/30 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/17 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.
Hull against the rest of the dataset
Hull's growing season runs about 154 days, ranking 34,332 of 40,283 US ZIP codes measured here, longest to shortest. Within IA, it ranks 897 of 1,042.
Learn more
Two guides worth reading on 51239: local microclimates, on what one yard in Hull can differ from the 51239 normal, and zone vs. frost date, on why Zone 5a and Hull's frost date answer different questions.