FrostCal

When to Plant Cosmos in Delaware

In a typical Delaware location, start seeds indoors Mar 10 – Mar 17, then sow outdoors Apr 14 – Apr 28, then transplant outdoors Apr 14 – Apr 21. Across the state, the outdoor planting window starts as early as Apr 6 in Claymont and as late as Apr 26 in Hockessin.

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
WilmingtonMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
DoverMar 7 – Mar 14Apr 11 – Apr 25Apr 11 – Apr 18
NewarkMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
MiddletownMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
BearMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
BrooksideMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
GlasgowMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
HockessinMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
SmyrnaMar 7 – Mar 14Apr 11 – Apr 25Apr 11 – Apr 18
Pike Creek ValleyMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
MilfordMar 14 – Mar 21Apr 18 – May 2Apr 18 – Apr 25
ClaymontMar 2 – Mar 9Apr 6 – Apr 20Apr 6 – Apr 13
North StarMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
Pike CreekMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
Wilmington ManorMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
SeafordMar 14 – Mar 21Apr 18 – May 2Apr 18 – Apr 25
GeorgetownMar 7 – Mar 14Apr 11 – Apr 25Apr 11 – Apr 18
ElsmereMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
EdgemoorMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21
New CastleMar 10 – Mar 17Apr 14 – Apr 28Apr 14 – Apr 21

Showing the 20 most populous of 20 Delaware cities. Dates are estimates from each city's NOAA frost normals and university extension timing guidelines. See all Delaware cities.

Frequently Asked Questions

When should I plant cosmos in Delaware?

In a typical Delaware location, start seeds indoors Mar 10 – Mar 17, then sow outdoors Apr 14 – Apr 28, then transplant outdoors Apr 14 – Apr 21. Across the state, the outdoor planting window starts as early as Apr 6 in Claymont and as late as Apr 26 in Hockessin.

When is the last frost in Delaware?

The average last spring frost in Delaware ranges from March 30 in Claymont to April 19 in Hockessin, 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 Delaware

When to plant cosmos in other states

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