Ontario, WI 54651 Frost Dates
Ontario, WI: when does the frost end?
Around 04/27 is the usual last spring frost, about 242 days away. Fall's first freeze usually shows up around 10/14, roughly 170 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Ontario in Zone 4b (-25 to -20°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
With roughly 7 weeks until Ontario's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 04/27 isn't a guarantee
04/27 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 05/11 and only about 1 year in 10 sees frost after that.
Ontario against the rest of the dataset
Ontario's growing season runs about 170 days, ranking 29,183 of 40,283 US ZIP codes measured here, longest to shortest. Within WI, it ranks 128 of 860.
Learn more
Before leaning on 54651's figures: local microclimates explains what one yard in Ontario can differ from the 54651 normal, while zone vs. frost date explains why Zone 4b and Ontario's frost date answer different questions.