Planting Guides
When to Plant Tomatoes in Denver: Complete Guide + Best Varieties
Denver, Colorado
USDA Zone 5a
Last Frost: May 10
Last updated: November 30, 2025
Learn exactly when to plant tomatoes in Denver with specific dates for Zone 5a. Compare 6 top varieties, get a complete timeline, and master Colorado's unique growing challenges.
— Image © PlantReference.org 2026
Quick Answer
Plant tomato seeds indoors March 28-April 4, transplant outdoors May 16-23 after Denver's May 9 last frost date. Choose cold-tolerant varieties like 'Stupice' and 'Early Girl' for Denver's 148-day growing season. Provide afternoon shade and consistent watering in Colorado's high-altitude and low-humidity.
TL;DR
Plant tomato seeds indoors March 28-April 4, transplant outdoors May 16-23 after Denver's May 9 last frost date. Choose varieties like 'Stupice' and 'Early Girl' for Denver's 148-day growing season. Colorado's high altitude and intense UV require consistent watering and afternoon shade protection.
Frequently Asked Questions
Can I direct sow tomatoes in Denver's Zone 5a climate?
Direct sowing tomatoes in Denver is not recommended due to the short growing season and variable spring weather. With only 148 days between the May 9 last frost and October 4 first frost, starting seeds indoors 6-7 weeks early is essential for successful harvests. Denver's clay soil warms slowly, often remaining below the 60°F (15°C) minimum required for tomato seed germination until late May or early June. By that time, direct-sown plants wouldn't mature before fall frost arrives.
Do I need season extension equipment for tomatoes in Denver?
Season extension tools significantly improve success rates for tomato growing in Denver, though they're not absolutely necessary for early varieties. Row covers or Wall-o-Water protectors help buffer Denver's dramatic temperature swings during May and September, allowing earlier planting and extended harvest.
Which tomato varieties handle Denver's wind and hail best?
Solanum lycopersicum 'Early Girl' and Solanum lycopersicum 'Stupice' demonstrate superior resilience to Denver's challenging weather conditions. Their compact growth habit and sturdy stems resist wind damage better than large indeterminate varieties.
How do I prevent sunscald on tomatoes at Denver's altitude?
Sunscald prevention requires understanding Denver's intense UV radiation at 5,280 feet elevation. Maintain dense foliage through proper fertilization and avoid excessive pruning that exposes fruits to direct afternoon sun. Many Denver gardeners over-prune thinking it improves air circulation, but this leaves fruits vulnerable to UV damage.
What's the best watering schedule for tomatoes in Denver's clay soil?
Denver's clay soil requires deep, infrequent watering rather than daily shallow applications. Water 2-3 times per week with 1-2 inches (2.5-5 cm) total, allowing water to penetrate 12-18 inches (30-45 cm) deep where tomato roots concentrate.
Can I grow heirloom tomatoes successfully in Denver?
Heirloom varieties face significant challenges in Denver's Zone 5a climate, but success is possible with proper variety selection and management. Solanum lycopersicum 'Cherokee Purple'} adapts better than most heirlooms to Colorado conditions, showing good tolerance for temperature fluctuations and moderate drought stress.
How do I know when Denver soil is ready for tomato transplanting?
Soil temperature matters more than air temperature for tomato transplanting success in Denver. Wait until soil reaches 60°F (15°C) at 4-inch (10 cm) depth for three consecutive days, typically occurring 7-10 days after the May 9 last frost date.
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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.
