FrostCal

When to Plant Onions in Wisconsin

In a typical Wisconsin location, start seeds indoors Feb 19 – Mar 5, then transplant outdoors Apr 2 – Apr 16. Across the state, the outdoor planting window starts as early as Mar 22 in Kenosha and as late as Apr 13 in Merrill.

Method Start indoors, then transplant
Days to maturity 90–120 days

Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings.

Onions Planting Dates by City

CityStart indoorsTransplant
MilwaukeeFeb 15 – Mar 1Mar 29 – Apr 12
MadisonFeb 20 – Mar 6Apr 3 – Apr 17
Green BayFeb 26 – Mar 12Apr 9 – Apr 23
KenoshaFeb 8 – Feb 22Mar 22 – Apr 5
RacineFeb 9 – Feb 23Mar 23 – Apr 6
AppletonFeb 23 – Mar 9Apr 6 – Apr 20
WaukeshaFeb 20 – Mar 6Apr 3 – Apr 17
Eau ClaireFeb 13 – Feb 27Mar 27 – Apr 10
OshkoshFeb 13 – Feb 27Mar 27 – Apr 10
JanesvilleFeb 15 – Mar 1Mar 29 – Apr 12
West AllisFeb 15 – Mar 1Mar 29 – Apr 12
La CrosseFeb 16 – Mar 2Mar 30 – Apr 13
North La CrosseFeb 12 – Feb 26Mar 26 – Apr 9
SheboyganFeb 14 – Feb 28Mar 28 – Apr 11
WauwatosaFeb 15 – Mar 1Mar 29 – Apr 12
Fond du LacFeb 16 – Mar 2Mar 30 – Apr 13
New BerlinFeb 22 – Mar 8Apr 5 – Apr 19
WausauFeb 25 – Mar 11Apr 8 – Apr 22
BrookfieldFeb 19 – Mar 5Apr 2 – Apr 16
GreenfieldFeb 22 – Mar 8Apr 5 – Apr 19
BeloitFeb 20 – Mar 6Apr 3 – Apr 17
FranklinFeb 22 – Mar 8Apr 5 – Apr 19
Menomonee FallsFeb 25 – Mar 11Apr 8 – Apr 22
Oak CreekFeb 11 – Feb 25Mar 25 – Apr 8
ManitowocFeb 19 – Mar 5Apr 2 – Apr 16
Sun PrairieFeb 20 – Mar 6Apr 3 – Apr 17
West BendFeb 20 – Mar 6Apr 3 – Apr 17
FitchburgFeb 20 – Mar 6Apr 3 – Apr 17
Stevens PointFeb 23 – Mar 9Apr 6 – Apr 20
SuperiorFeb 25 – Mar 11Apr 8 – Apr 22

Showing the 30 most populous of 96 Wisconsin cities. Dates are estimates from each city's NOAA frost normals and university extension timing guidelines. See all Wisconsin cities.

Frequently Asked Questions

When should I plant onions in Wisconsin?

In a typical Wisconsin location, start seeds indoors Feb 19 – Mar 5, then transplant outdoors Apr 2 – Apr 16. Across the state, the outdoor planting window starts as early as Mar 22 in Kenosha and as late as Apr 13 in Merrill.

When is the last frost in Wisconsin?

The average last spring frost in Wisconsin ranges from April 19 in Kenosha to May 11 in Merrill, based on NOAA 1991–2020 climate normals.

How long do onions take to grow?

Onions typically take 90–120 days from planting to harvest. Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings.

Other Crops in Wisconsin

When to plant onions in other states

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