When to plant Summer squash (zucchini) in Colorado

In spring, from Apr 20 – June 1 in Grand Junction to June 10 – 20 in Steamboat Springs.

In fall, June 1 – July 1.

USDA's earliest safe spring and latest safe fall planting dates, matched to each place's average frost dates.

Summer squash planting dates by place in Colorado
PlaceSpringFall
ArvadaMay 1 – 30June 1 – July 1
AuroraMay 10 – June 10June 1 – July 15
BerthoudMay 10 – June 10June 1 – July 1
BoulderMay 10 – June 10June 1 – July 1
BrightonMay 1 – 30June 1 – July 15
BroomfieldMay 1 – 30June 1 – July 15
Cañon CityMay 1 – 30June 1 – July 15
Castle PinesMay 10 – June 10June 1 – July 1
Castle RockMay 10 – June 10June 1 – July 1
CentennialMay 1 – 30June 1 – July 15
Colorado SpringsMay 1 – 30June 1 – July 15
Commerce CityMay 1 – 30June 1 – July 15
DenverMay 1 – 30June 1 – July 15
DurangoMay 20 – June 15June 1 – July 1
EnglewoodMay 1 – 30June 1 – July 15
ErieMay 10 – June 10June 1 – July 1
EvansMay 1 – 30June 1 – July 15
Federal HeightsMay 1 – 30June 1 – July 15
FirestoneMay 10 – June 10June 1 – July 1
Fort CollinsMay 1 – 30June 1 – July 15
Fort MorganMay 10 – June 10June 1 – July 15
FountainMay 1 – 30June 1 – July 15
FrederickMay 10 – June 10June 1 – July 1
FruitaMay 1 – 30June 1 – July 15
Glenwood SpringsMay 10 – June 10June 1 – July 1
GoldenMay 1 – 30June 1 – July 15
Grand JunctionApr 20 – June 1June 1 – July 20
GreeleyMay 1 – 30June 1 – July 15
Greenwood VillageMay 10 – June 10June 1 – July 15
JohnstownMay 10 – June 10June 1 – July 1
LafayetteMay 1 – 30June 1 – July 15
LakewoodMay 1 – 30June 1 – July 15
LittletonMay 1 – 30June 1 – July 15
Lone TreeMay 1 – 30June 1 – July 15
LongmontMay 10 – June 10June 1 – July 1
LouisvilleMay 10 – June 10June 1 – July 1
LovelandMay 10 – June 10June 1 – July 1
MontroseMay 1 – 30June 1 – July 15
MonumentMay 20 – June 15June 1 – July 1
NorthglennMay 1 – 30June 1 – July 15
ParkerMay 10 – June 10June 1 – July 1
PuebloMay 1 – 30June 1 – July 15
RifleMay 10 – June 10June 1 – July 1
SeveranceMay 1 – 30June 1 – July 15
Steamboat SpringsJune 10 – 20June 1 – 20
SterlingMay 1 – 30June 1 – July 15
SuperiorMay 10 – June 10June 1 – July 1
ThorntonMay 1 – 30June 1 – July 15
TimnathMay 1 – 30June 1 – July 15
WellingtonMay 1 – 30June 1 – July 15
WestminsterMay 1 – 30June 1 – July 15
Wheat RidgeMay 1 – 30June 1 – July 1
WindsorMay 1 – 30June 1 – July 15

Planting dates: USDA Home and Garden Bulletin No. 9 (1967), tables 4 and 5. Frost dates: NOAA U.S. Climate Normals 1991–2020. “—” means the place's frost date is outside the table. The full USDA table for summer squash.