Colorado · zones 5a–7a
When to plant watermelon in Colorado.
Sow between May 30 to Jun 29 in a typical year, keyed to Colorado's median last frost around May 9. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Watermelon dates for a typical Colorado season.
Direct sow
May 30 to Jun 29
Keyed to the ~May 9 last frost. Sow 1" deep, 36" apart.
Harvest
~85 days later
~20 lb per plant over ~3 weeks.
Colorado spans more than one climate: Zone 6 is the most common zone, but the state runs 5a to 7a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
In Colorado: watch for
The pests that find watermelon here.
The short season here, about 143 frost-free days, keeps watermelon in front of cucumber beetles only briefly. One early row cover usually carries a planting through the worst of it.
Striped or spotted beetles chewing leaves, blossoms and rinds.
Organic fix: Row cover until the first female flowers open, then hand-pick in the morning.
Clusters on the growing tips; sticky film on the leaves below.
Organic fix: Hose them off, or use insecticidal soap.
Anthracnose & gummy stem blight
Dark sunken spots on leaves and fruit after a humid stretch.
Organic fix: Rotate away from cucurbits, keep foliage dry, remove infected vines.
Your season math: Colorado gives watermelon about 143 frost-free days, and it needs roughly 85 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting watermelon in Colorado: questions
When should I plant watermelon in Colorado?+
In a typical Colorado year, sow watermelon between May 30 to Jun 29, keyed to the state's median last frost around May 9. Your exact dates shift with your ZIP code and microclimate.
What USDA zone is Colorado?+
Colorado spans zones 5a–7a, mostly zone 6. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many watermelon plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.