Niagara, WI 54151 Frost Dates
Niagara, WI: when does the frost end?
Typically, the last spring freeze lands around 05/17, roughly 262 days out. Fall's first freeze usually shows up around 10/01, roughly 135 days after the last spring frost.
Zone 4b (-25 to -20°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 Niagara, not a forecast for this year.
Stretching the season past the first frost
With roughly 5 weeks until Niagara's first fall frost, a row cover or cold frame is what stretches the last few weeks of harvest here.
Why 05/17 isn't a guarantee
05/17 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/02 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/31 and only about 1 year in 10 sees frost after that.
Niagara against the rest of the dataset
Niagara's growing season runs about 135 days, ranking 37,873 of 40,283 US ZIP codes measured here, longest to shortest. Within WI, it ranks 772 of 860.
Learn more
Before leaning on 54151's figures: zone vs. frost date explains why Zone 4b and Niagara's frost date answer different questions, while the frost range explains how to read the range around Niagara's dates instead of trusting one.