Planting Guides
When to Plant Kale in Denver: Complete Guide + Best Varieties for Zone 5a
Denver, Colorado
USDA Zone 5a
Last Frost: May 10
Last updated: October 30, 2025
Plant kale in Denver for spring harvest April 15-25, fall harvest July 15-August 1. Zone 5a's 148-day season and May 9 frost date create perfect conditions.
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Quick Answer
Plant kale in Denver April 15-25 for spring harvest or July 15-August 1 for fall crops. Zone 5a's May 9 frost date allows excellent spring and fall growing windows.
TL;DR
Plant kale in Denver April 15-25 for spring harvest or July 15-August 1 for superior fall crops. Zone 5a's 148-day season and May 9 last frost create ideal conditions for Brassica oleracea 'Winterbor' and Brassica oleracea 'Lacinato'. Fall plantings survive Denver's October 4 first frost and produce sweeter leaves through winter with protection.
Frequently Asked Questions
When should I plant kale seeds in Denver for the best harvest?
Plant kale in Denver July 15-August 1 for the superior fall harvest or April 15-25 for spring crops. Fall plantings consistently outperform spring ones because Denver's October frost triggers the sweetening process that makes kale tender and flavorful. Spring planting works but must be timed carefully to harvest before summer heat causes bolting and bitterness.
What kale varieties grow best in Denver's Zone 5a climate?
Brassica oleracea 'Winterbor' and Brassica oleracea 'Lacinato' perform best in Denver's high-altitude conditions. Winterbor handles Denver's dramatic temperature swings and survives winter temperatures to -15°F. Lacinato tolerates the intense UV radiation and low humidity better than curly varieties. Both varieties mature in 60-75 days, perfect for Denver's 148-day growing season.
How cold can kale survive in Denver winters?
Kale survives Denver winter temperatures down to 20°F without protection and to -10°F with row covers. Brassica oleracea 'Winterbor' and Brassica oleracea 'Redbor' show the best cold tolerance. Frost actually improves flavor by converting starches to sugars, making post-frost kale dramatically sweeter. Mulch plants heavily and use row covers during the coldest periods for continuous winter harvest.
Why does my spring kale bolt so quickly in Denver?
Denver's rapid temperature swings from cool nights to hot days trigger stress bolting in spring kale. When temperatures jump from 40°F to 85°F in 24 hours—common during chinook winds—kale interprets this as seasonal change and bolts to flower. Plant bolt-resistant varieties like Brassica oleracea 'Lacinato' for spring crops and provide afternoon shade during heat waves above 85°F.
How often should I water kale in Denver's dry climate?
Water kale 1-2 inches weekly in one deep application rather than daily light watering. Denver's clay soil and low humidity require modified watering techniques. Water early morning to minimize evaporation losses and apply 2-3 inches of mulch to conserve soil moisture. Check soil moisture 3 inches deep—clay holds water longer than it appears on the surface.
Can I grow kale year-round in Denver?
Yes, with proper varieties and season extension techniques. Plant Brassica oleracea 'Winterbor' in July for harvest through February, then start spring crops in March for June harvest. Use cold frames and row covers during winter to maintain harvesting access. Denver's intense winter sun heats protected plants effectively, making year-round growing possible with 2-3 months of season extension infrastructure.
What's the biggest mistake Denver gardeners make with kale?
Planting too late for fall crops. Many gardeners wait until September to plant fall kale, but Denver's October 4 first frost requires planting by August 1 at the latest for full-size plants. Late plantings produce only baby greens before hard freeze. Fall kale planted July 15-August 1 develops cold tolerance and produces sweet, tender leaves all winter with minimal protection.
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Written By
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Nathan Brooks
Nathan is a garden designer in Denver who focuses on water-wise plantings adapted to Colorado's Front Range climate. He grew up in Nebraska, studied environmental science in college, and fell into garden design after spending summers working at a native plant nursery in Fort Collins. Denver's climate is genuinely challenging—low humidity, intense UV, alkaline clay soil, and wild temperature swings that can go from 70°F to snow in 24 hours. Nathan designs gardens that handle all of that without supplemental irrigation once established. He writes about xeric gardening, native plant selection for the Front Range, and the practical realities of high-altitude growing.
