FrostCal

When to Plant Cosmos in Iowa

In a typical Iowa location, start seeds indoors Mar 24 – Mar 31, then sow outdoors Apr 28 – May 12, then transplant outdoors Apr 28 – May 5. Across the state, the outdoor planting window starts as early as Apr 17 in Keokuk and as late as May 10 in Grinnell.

Method Direct sow
Days to maturity 60–90 days

Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early.

Cosmos Planting Dates by City

CityStart indoorsDirect sowTransplant
Des MoinesMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
Cedar RapidsMar 31 – Apr 7May 5 – May 19May 5 – May 12
DavenportMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
Sioux CityApr 1 – Apr 8May 6 – May 20May 6 – May 13
Iowa CityMar 24 – Mar 31Apr 28 – May 12Apr 28 – May 5
WaterlooMar 30 – Apr 6May 4 – May 18May 4 – May 11
AmesMar 29 – Apr 5May 3 – May 17May 3 – May 10
West Des MoinesMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
Council BluffsMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
DubuqueMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
AnkenyMar 26 – Apr 2Apr 30 – May 14Apr 30 – May 7
UrbandaleMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
Cedar FallsMar 30 – Apr 6May 4 – May 18May 4 – May 11
MarionMar 31 – Apr 7May 5 – May 19May 5 – May 12
BettendorfMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
MarshalltownMar 31 – Apr 7May 5 – May 19May 5 – May 12
Mason CityApr 1 – Apr 8May 6 – May 20May 6 – May 13
ClintonMar 16 – Mar 23Apr 20 – May 4Apr 20 – Apr 27
BurlingtonMar 18 – Mar 25Apr 22 – May 6Apr 22 – Apr 29
Fort DodgeMar 31 – Apr 7May 5 – May 19May 5 – May 12
OttumwaMar 26 – Apr 2Apr 30 – May 14Apr 30 – May 7
MuscatineMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
JohnstonMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
CoralvilleMar 24 – Mar 31Apr 28 – May 12Apr 28 – May 5
WaukeeMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
AltoonaMar 24 – Mar 31Apr 28 – May 12Apr 28 – May 5
North LibertyMar 24 – Mar 31Apr 28 – May 12Apr 28 – May 5
IndianolaMar 27 – Apr 3May 1 – May 15May 1 – May 8
CliveMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
NewtonMar 25 – Apr 1Apr 29 – May 13Apr 29 – May 6

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 cosmos in Iowa?

In a typical Iowa location, start seeds indoors Mar 24 – Mar 31, then sow outdoors Apr 28 – May 12, then transplant outdoors Apr 28 – May 5. Across the state, the outdoor planting window starts as early as Apr 17 in Keokuk and as late as May 10 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 cosmos take to grow?

Cosmos typically take 60–90 days from planting to harvest. Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early.

Other Crops in Iowa

When to plant cosmos in other states

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