FrostCal

When to Plant Onions in Colorado

In a typical Colorado location, start seeds indoors Feb 22 – Mar 8, then transplant outdoors Apr 5 – Apr 19. Across the state, the outdoor planting window starts as early as Mar 17 in Grand Junction and as late as May 24 in Edwards.

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
DenverFeb 19 – Mar 5Apr 2 – Apr 16
Colorado SpringsFeb 22 – Mar 8Apr 5 – Apr 19
AuroraFeb 23 – Mar 9Apr 6 – Apr 20
Fort CollinsFeb 21 – Mar 7Apr 4 – Apr 18
LakewoodFeb 22 – Mar 8Apr 5 – Apr 19
ThorntonFeb 21 – Mar 7Apr 4 – Apr 18
WestminsterFeb 21 – Mar 7Apr 4 – Apr 18
ArvadaFeb 24 – Mar 10Apr 7 – Apr 21
CentennialFeb 24 – Mar 10Apr 7 – Apr 21
PuebloFeb 19 – Mar 5Apr 2 – Apr 16
GreeleyFeb 21 – Mar 7Apr 4 – Apr 18
BoulderFeb 25 – Mar 11Apr 8 – Apr 22
Highlands RanchFeb 24 – Mar 10Apr 7 – Apr 21
LongmontFeb 26 – Mar 12Apr 9 – Apr 23
LovelandMar 1 – Mar 15Apr 12 – Apr 26
BroomfieldFeb 21 – Mar 7Apr 4 – Apr 18
Grand JunctionFeb 3 – Feb 17Mar 17 – Mar 31
Castle RockFeb 28 – Mar 14Apr 11 – Apr 25
Commerce CityFeb 23 – Mar 9Apr 6 – Apr 20
ParkerFeb 28 – Mar 14Apr 11 – Apr 25
LittletonFeb 21 – Mar 7Apr 4 – Apr 18
NorthglennFeb 21 – Mar 7Apr 4 – Apr 18
BrightonFeb 22 – Mar 8Apr 5 – Apr 19
Dakota RidgeFeb 21 – Mar 7Apr 4 – Apr 18
EnglewoodFeb 21 – Mar 7Apr 4 – Apr 18
Security-WidefieldFeb 22 – Mar 8Apr 5 – Apr 19
WindsorFeb 22 – Mar 8Apr 5 – Apr 19
Ken CarylFeb 21 – Mar 7Apr 4 – Apr 18
Wheat RidgeFeb 24 – Mar 10Apr 7 – Apr 21
Pueblo WestFeb 15 – Mar 1Mar 29 – Apr 12

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 onions in Colorado?

In a typical Colorado location, start seeds indoors Feb 22 – Mar 8, then transplant outdoors Apr 5 – Apr 19. Across the state, the outdoor planting window starts as early as Mar 17 in Grand Junction and as late as May 24 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 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 Colorado

When to plant onions in other states

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