When to plant onions in Colorado

Onions
Plant out in Denver
Mar 23–Apr 13

Across Colorado the window opens between March 3 and March 29. Find your city below; the dates follow each town's own average last frost.

Start indoors, Denver
Feb 9–Mar 9
Plant out, Denver
Mar 23–Apr 13
Last frost, Denver
May 4

Start seeds indoors 8–12 weeks before the last frost; plant out 3–6 weeks before the last frost. Northern gardens need long-day varieties and southern gardens need short-day ones. A wrong pick gives small bulbs.

Onions planting dates by city

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost
JanFebMarAprMayJunJulAugSepOctNovDec
DenverMar 23–Apr 13
Colorado SpringsMar 22–Apr 12
AuroraMar 26–Apr 16
Fort CollinsMar 21–Apr 11
LakewoodMar 22–Apr 12
ThorntonMar 21–Apr 11
ArvadaMar 24–Apr 14
WestminsterMar 21–Apr 11
GreeleyMar 21–Apr 11
PuebloMar 19–Apr 9
CentennialMar 24–Apr 14
BoulderMar 25–Apr 15
LongmontMar 26–Apr 16
LovelandMar 29–Apr 19
BroomfieldMar 21–Apr 11
Commerce CityMar 22–Apr 12
Grand JunctionMar 3–Mar 24
LittletonMar 21–Apr 11
BrightonMar 22–Apr 12
WindsorMar 22–Apr 12
ErieMar 26–Apr 16
NorthglennMar 21–Apr 11
Security-WidefieldMar 22–Apr 12
EnglewoodMar 21–Apr 11
Pueblo WestMar 15–Apr 5
Wheat RidgeMar 24–Apr 14
LafayetteMar 21–Apr 11
FountainMar 22–Apr 12
EvansMar 21–Apr 11
JohnstownMar 29–Apr 19
All 34 cities
CityStart indoorsPlant outLast frost
DenverFeb 9 to Mar 9Mar 23 to Apr 13May 4
Colorado SpringsFeb 8 to Mar 8Mar 22 to Apr 12May 3
AuroraFeb 12 to Mar 12Mar 26 to Apr 16May 7
Fort CollinsFeb 7 to Mar 7Mar 21 to Apr 11May 2
LakewoodFeb 8 to Mar 8Mar 22 to Apr 12May 3
ThorntonFeb 7 to Mar 7Mar 21 to Apr 11May 2
ArvadaFeb 10 to Mar 10Mar 24 to Apr 14May 5
WestminsterFeb 7 to Mar 7Mar 21 to Apr 11May 2
GreeleyFeb 7 to Mar 7Mar 21 to Apr 11May 2
PuebloFeb 5 to Mar 5Mar 19 to Apr 9Apr 30
CentennialFeb 10 to Mar 10Mar 24 to Apr 14May 5
BoulderFeb 11 to Mar 11Mar 25 to Apr 15May 6
LongmontFeb 12 to Mar 12Mar 26 to Apr 16May 7
LovelandFeb 15 to Mar 15Mar 29 to Apr 19May 10
BroomfieldFeb 7 to Mar 7Mar 21 to Apr 11May 2
Commerce CityFeb 8 to Mar 8Mar 22 to Apr 12May 3
Grand JunctionJan 20 to Feb 17Mar 3 to Mar 24Apr 14
LittletonFeb 7 to Mar 7Mar 21 to Apr 11May 2
BrightonFeb 8 to Mar 8Mar 22 to Apr 12May 3
WindsorFeb 8 to Mar 8Mar 22 to Apr 12May 3
ErieFeb 12 to Mar 12Mar 26 to Apr 16May 7
NorthglennFeb 7 to Mar 7Mar 21 to Apr 11May 2
Security-WidefieldFeb 8 to Mar 8Mar 22 to Apr 12May 3
EnglewoodFeb 7 to Mar 7Mar 21 to Apr 11May 2
Pueblo WestFeb 1 to Mar 1Mar 15 to Apr 5Apr 26
Wheat RidgeFeb 10 to Mar 10Mar 24 to Apr 14May 5
LafayetteFeb 7 to Mar 7Mar 21 to Apr 11May 2
FountainFeb 8 to Mar 8Mar 22 to Apr 12May 3
EvansFeb 7 to Mar 7Mar 21 to Apr 11May 2
JohnstownFeb 15 to Mar 15Mar 29 to Apr 19May 10
Four Square MileFeb 12 to Mar 12Mar 26 to Apr 16May 7
MontroseFeb 3 to Mar 3Mar 17 to Apr 7Apr 28
LouisvilleFeb 11 to Mar 11Mar 25 to Apr 15May 6
FirestoneFeb 12 to Mar 12Mar 26 to Apr 16May 7

Questions

When should I plant onions in Colorado?

In Denver, plant out from March 23 to April 13. Across Colorado the window opens between March 3 and March 29, depending on the local last frost.

How is this date worked out?

Start seeds indoors 8–12 weeks before the last frost; plant out 3–6 weeks before the last frost. Frost dates are NOAA 1991–2020 averages for the weather station nearest each city.

More for Colorado

Onions in other states

Frost dates for every city in Colorado