FrostCal

When to Plant Onions in Iowa

In a typical Iowa location, start seeds indoors Feb 10 – Feb 24, then transplant outdoors Mar 24 – Apr 7. Across the state, the outdoor planting window starts as early as Mar 13 in Keokuk and as late as Apr 5 in Grinnell.

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
Des MoinesFeb 7 – Feb 21Mar 21 – Apr 4
Cedar RapidsFeb 17 – Mar 3Mar 31 – Apr 14
DavenportFeb 8 – Feb 22Mar 22 – Apr 5
Sioux CityFeb 18 – Mar 4Apr 1 – Apr 15
Iowa CityFeb 10 – Feb 24Mar 24 – Apr 7
WaterlooFeb 16 – Mar 2Mar 30 – Apr 13
AmesFeb 15 – Mar 1Mar 29 – Apr 12
West Des MoinesFeb 7 – Feb 21Mar 21 – Apr 4
Council BluffsFeb 7 – Feb 21Mar 21 – Apr 4
DubuqueFeb 8 – Feb 22Mar 22 – Apr 5
AnkenyFeb 12 – Feb 26Mar 26 – Apr 9
UrbandaleFeb 7 – Feb 21Mar 21 – Apr 4
Cedar FallsFeb 16 – Mar 2Mar 30 – Apr 13
MarionFeb 17 – Mar 3Mar 31 – Apr 14
BettendorfFeb 8 – Feb 22Mar 22 – Apr 5
MarshalltownFeb 17 – Mar 3Mar 31 – Apr 14
Mason CityFeb 18 – Mar 4Apr 1 – Apr 15
ClintonFeb 2 – Feb 16Mar 16 – Mar 30
BurlingtonFeb 4 – Feb 18Mar 18 – Apr 1
Fort DodgeFeb 17 – Mar 3Mar 31 – Apr 14
OttumwaFeb 12 – Feb 26Mar 26 – Apr 9
MuscatineFeb 7 – Feb 21Mar 21 – Apr 4
JohnstonFeb 8 – Feb 22Mar 22 – Apr 5
CoralvilleFeb 10 – Feb 24Mar 24 – Apr 7
WaukeeFeb 8 – Feb 22Mar 22 – Apr 5
AltoonaFeb 10 – Feb 24Mar 24 – Apr 7
North LibertyFeb 10 – Feb 24Mar 24 – Apr 7
IndianolaFeb 13 – Feb 27Mar 27 – Apr 10
CliveFeb 7 – Feb 21Mar 21 – Apr 4
NewtonFeb 11 – Feb 25Mar 25 – Apr 8

Showing the 30 most populous of 45 Iowa cities. Dates are estimates from each city's NOAA frost normals and university extension timing guidelines. See all Iowa cities.

Frequently Asked Questions

When should I plant onions in Iowa?

In a typical Iowa location, start seeds indoors Feb 10 – Feb 24, then transplant outdoors Mar 24 – Apr 7. Across the state, the outdoor planting window starts as early as Mar 13 in Keokuk and as late as Apr 5 in Grinnell.

When is the last frost in Iowa?

The average last spring frost in Iowa ranges from April 10 in Keokuk to May 3 in Grinnell, 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 Iowa

When to plant onions in other states

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