Colorado · zones 5a–7a
When to plant kale in Colorado.
Sow or transplant between Apr 1 to Apr 29 in a typical year, keyed to Colorado's median last frost around May 9. A second, fall sowing fits Jun 29 to Aug 14. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Kale dates for a typical Colorado season.
1 · Start indoors
Feb 18 to Mar 18
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Apr 1 to Apr 29
Keyed to the ~May 9 last frost. Sow 0.25" deep, 16" apart.
Fall round
Jun 29 to Aug 14
Counted back from the ~Sep 29 first frost.
Harvest
~45 days later
~2 lb per plant over ~16 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.
Colorado growing notes
Kale takes a Colorado hailstorm better than almost anything else in the bed.
Cold-bred varieties for a state that tests them
Kale evolved to survive frost, and Colorado gardens above 5,000 feet put that trait to real use: Red Russian and Winterbor both hold flavor and texture through nights in the high 20s, while Dwarf Blue Curled Vates stays compact enough for a wind-exposed bed. Any of the three will outlast a June hailstorm that shreds squash and beans down to stubs, because kale's growing point sits low and close to the crown.
The same intense sun that browns a gardener's arms in July is doing something specific to the leaf: elevation adds roughly 4 percent more ultraviolet exposure for every 1,000 feet of gain, and a garden at 6,500 feet, common along the Front Range foothills, is getting close to a quarter more UV than a sea-level plot. Kale answers by thickening its cuticle and deepening its color; leaves that stay pale green past the 4-leaf stage are usually asking for nitrogen, not shade or extra water. Side-dress with a balanced fertilizer and check back in 2 weeks: the next flush of leaves should come in noticeably darker if that was the problem.
Working alkaline clay instead of fighting it
Front Range soil commonly tests pH 7.0 to 8.0, sitting on clay derived from old shale and limestone, and kale is one of the few garden crops that does not mind the alkalinity at all. What it minds is the clay itself: dig a 12-inch test hole, fill it with water, and time the drain; under an hour is workable ground, but water still sitting there hours later means you owe the bed a couple of inches of compost turned through the top spade depth before anything gets transplanted, since that structure problem will suffocate kale roots long before the pH ever does.
High pH can still lock up iron, and kale grown in raw, unamended clay sometimes shows chlorosis, a yellowing between the veins while the veins themselves stay green. A dose of chelated iron corrects it within 2 weeks. Nitrogen is the other nutrient to manage actively here: split it into 3 small feedings across the season rather than one heavy dose, since alkaline clay releases nitrogen more slowly and unevenly than the sandier soils kale tolerates just as well elsewhere.
Flea beetles move in fast at this elevation
Flea beetles are the one pest that reliably out-paces Colorado kale, riddling seedling leaves with pinholes within days of emergence. Run the test weekly: leaves peppered with fresh pinholes, or beetles that visibly jump when you brush the plant, means row cover goes on that afternoon, not next weekend. A leaf with just a scattering of holes usually outgrows the damage on its own once true leaves harden off.
Cover stays on until plants carry 6 true leaves and a stem woody enough to shrug off minor grazing, since kale needs no pollinator to make a harvestable crop, unlike the squash and beans sharing the same hail season. Keep kale out of any bed that grew broccoli, cabbage, or other brassicas in the last 2 years; flea beetles and cabbage worms both overwinter in the soil and pick up exactly where the last brassica crop left off.
In Colorado: watch for
The pests that find kale here.
The short season here, about 143 frost-free days, keeps kale in front of cabbage worms & loopers only briefly. One early row cover usually carries a planting through the worst of it.
Green caterpillars chewing ragged holes; green droppings.
Organic fix: Handpick, cover with netting, spray Bt.
Gray-green clusters tucked into the leaf folds.
Organic fix: Blast with water, then insecticidal soap.
Tiny holes peppering the young leaves.
Organic fix: Row cover from day one; diatomaceous earth.
Black rot
Yellow V-shaped wedges cutting in from the leaf edge, veins blackening inside.
Organic fix: Pull infected plants, water at the base, keep brassicas out of that bed 3 years.
Seedlings wilt, yellow and stall for no reason; white maggots tunnel the roots.
Organic fix: Row cover before the flies are up, when yellow rocket blooms; rotate the bed.
Your season math: Colorado gives kale about 143 frost-free days, and it needs roughly 45 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting kale in Colorado: questions
When should I plant kale in Colorado?+
In a typical Colorado year, sow kale or set out transplants between Apr 1 to Apr 29, keyed to the state's median last frost around May 9. There's also a fall window: Jun 29 to Aug 14. Your exact dates shift with your ZIP code and microclimate.
When do I start kale seeds indoors in Colorado?+
Start seeds inside about 6 weeks before set-out: roughly Feb 18 to Mar 18 for a typical Colorado season.
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 kale 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.