Colorado · zones 5a–7a
When to plant sweet corn in Colorado.
Sow between May 16 to Jul 9 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
Sweet Corn dates for a typical Colorado season.
Direct sow
May 16 to Jul 9
Keyed to the ~May 9 last frost. Sow 1.5" deep, 12" apart.
Harvest
~75 days later
~1 lb per plant over ~1 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 sweet corn here.
The short season here, about 143 frost-free days, keeps sweet corn in front of corn earworm only briefly. One early row cover usually carries a planting through the worst of it.
Caterpillars feeding down in the tip of the ear.
Organic fix: A few drops of oil on the silk; Bt on the silks.
Broken tassels and frass-filled holes in the stalk.
Organic fix: Bt on young plants; cut and destroy stalks after harvest.
Clusters on the tassels and upper leaves.
Organic fix: Usually minor; insecticidal soap if heavy.
Fall armyworm
Ragged holes through the unfurling whorl leaves, with sawdust-like droppings down in the funnel.
Organic fix: Check whorls weekly before tassel; Bt or spinosad while the caterpillars are still small.
Cinnamon-brown powdery pustules breaking out on BOTH sides of the same leaf, lower leaves first, darkening as they age.
Organic fix: Water at the ground rather than overhead, and choose resistant varieties next season; sprays are rarely worth it.
Your season math: Colorado gives sweet corn about 143 frost-free days, and it needs roughly 75 days to a first harvest. That fits about 7 re-sown rounds across the season, so you can keep it coming instead of picking once.
Planting sweet corn in Colorado: questions
When should I plant sweet corn in Colorado?+
In a typical Colorado year, sow sweet corn between May 16 to Jul 9, 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 sweet corn 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.