Johnston, IA 50131 Frost Dates
50131, near Johnston, IA: the frost window
Around 04/19 is the usual last spring frost, about 234 days away. Fall's first freeze usually shows up around 10/18, roughly 179 days after the last spring frost.
Zone 5b (-15 to -10°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 Johnston, not a forecast for this year.
Stretching the season past the first frost
Johnston's growing season runs out in roughly 7 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
04/19 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/05 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/03 and only about 1 year in 10 sees frost after that.
Johnston against the rest of the dataset
At roughly 179 frost-free days, Johnston places 25,192 of 40,283 ZIP codes in this dataset. Within IA, it ranks 97 of 1,042.
Learn more
Two guides worth reading on 50131: local microclimates, on what one yard in Johnston can differ from the 50131 normal, and zone vs. frost date, on why Zone 5b and Johnston's frost date answer different questions.