FrostCal

When to Plant Cosmos in Colorado

In a typical Colorado location, start seeds indoors Apr 5 – Apr 12, then sow outdoors May 10 – May 24, then transplant outdoors May 10 – May 17. Across the state, the outdoor planting window starts as early as Apr 21 in Grand Junction and as late as Jun 28 in Edwards.

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
DenverApr 2 – Apr 9May 7 – May 21May 7 – May 14
Colorado SpringsApr 5 – Apr 12May 10 – May 24May 10 – May 17
AuroraApr 6 – Apr 13May 11 – May 25May 11 – May 18
Fort CollinsApr 4 – Apr 11May 9 – May 23May 9 – May 16
LakewoodApr 5 – Apr 12May 10 – May 24May 10 – May 17
ThorntonApr 4 – Apr 11May 9 – May 23May 9 – May 16
WestminsterApr 4 – Apr 11May 9 – May 23May 9 – May 16
ArvadaApr 7 – Apr 14May 12 – May 26May 12 – May 19
CentennialApr 7 – Apr 14May 12 – May 26May 12 – May 19
PuebloApr 2 – Apr 9May 7 – May 21May 7 – May 14
GreeleyApr 4 – Apr 11May 9 – May 23May 9 – May 16
BoulderApr 8 – Apr 15May 13 – May 27May 13 – May 20
Highlands RanchApr 7 – Apr 14May 12 – May 26May 12 – May 19
LongmontApr 9 – Apr 16May 14 – May 28May 14 – May 21
LovelandApr 12 – Apr 19May 17 – May 31May 17 – May 24
BroomfieldApr 4 – Apr 11May 9 – May 23May 9 – May 16
Grand JunctionMar 17 – Mar 24Apr 21 – May 5Apr 21 – Apr 28
Castle RockApr 11 – Apr 18May 16 – May 30May 16 – May 23
Commerce CityApr 6 – Apr 13May 11 – May 25May 11 – May 18
ParkerApr 11 – Apr 18May 16 – May 30May 16 – May 23
LittletonApr 4 – Apr 11May 9 – May 23May 9 – May 16
NorthglennApr 4 – Apr 11May 9 – May 23May 9 – May 16
BrightonApr 5 – Apr 12May 10 – May 24May 10 – May 17
Dakota RidgeApr 4 – Apr 11May 9 – May 23May 9 – May 16
EnglewoodApr 4 – Apr 11May 9 – May 23May 9 – May 16
Security-WidefieldApr 5 – Apr 12May 10 – May 24May 10 – May 17
WindsorApr 5 – Apr 12May 10 – May 24May 10 – May 17
Ken CarylApr 4 – Apr 11May 9 – May 23May 9 – May 16
Wheat RidgeApr 7 – Apr 14May 12 – May 26May 12 – May 19
Pueblo WestMar 29 – Apr 5May 3 – May 17May 3 – May 10

Showing the 30 most populous of 65 Colorado cities. Dates are estimates from each city's NOAA frost normals and university extension timing guidelines. See all Colorado cities.

Frequently Asked Questions

When should I plant cosmos in Colorado?

In a typical Colorado location, start seeds indoors Apr 5 – Apr 12, then sow outdoors May 10 – May 24, then transplant outdoors May 10 – May 17. Across the state, the outdoor planting window starts as early as Apr 21 in Grand Junction and as late as Jun 28 in Edwards.

When is the last frost in Colorado?

The average last spring frost in Colorado ranges from April 14 in Grand Junction to June 21 in Edwards, 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 Colorado

When to plant cosmos in other states

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