Planting Guides

When to Plant Cucumbers in Denver: Complete Guide + Best Varieties for Zone 5a

Denver, Colorado

USDA Zone 5a

Last Frost: May 10

Last updated: October 30, 2025

Learn when to plant cucumbers in Denver with specific dates for Zone 5a. Compare 6 varieties perfect for Colorado's climate and get expert timing tips.

NNathan Brooks

October 30, 2025

Transplanting cucumber seedlings in Denver garden with Rocky Mountains backdrop showing proper Zone 5a planting timing — — Image © PlantReference.org 2026

Quick Answer

Plant cucumbers in Denver after May 10 last frost date. Start seeds indoors March 15-22 for transplanting May 15-22.

TL;DR

Plant cucumbers in Denver after May 10 when soil reaches 60°F consistently. Start seeds indoors March 15-22 for transplanting May 15-22, or direct sow May 25-June 1. Choose cold-hardy varieties like Cucumis sativus 'Boston Pickling' or Cucumis sativus 'Marketmore 76' for Denver's short 148-day growing season in Zone 5a.

Frequently Asked Questions

When is the last safe date to plant cucumbers in Denver?

June 15 is the absolute last date for planting 50-day varieties like Cucumis sativus 'Boston Pickling' in Denver. Longer-season varieties should be planted by June 1 to ensure harvest before October's first frost. Late plantings risk being damaged by early fall cold snaps that can occur before the average October 5 first frost date.

Can I grow cucumbers successfully at Denver's high altitude?

Yes, cucumbers can thrive at Denver's 5,280-foot elevation (~1,600 meters) with proper variety selection and techniques. Choose cold-hardy, short-season varieties and provide protection from intense UV radiation with afternoon shade. The key is working with Denver's 148-day growing season rather than fighting it.

Should I start cucumber seeds indoors or direct sow in Denver?

For Denver's Zone 5a climate, starting seeds indoors gives the best results. Begin seeds March 15-22 in biodegradable peat pots and transplant outdoors May 15-22. This method provides 2-3 weeks advantage over direct sowing and ensures harvest before fall frost.

What soil temperature is needed for cucumber germination in Denver?

Cucumber seeds require soil temperatures of 60°F (16°C) minimum, with 65-70°F (18-21°C) optimal for germination in Denver. Measure soil temperature at 4-inch (10 cm) depth for three consecutive mornings before planting. Cold soil below 60°F (16°C) will cause seeds to rot rather than germinate.

How do I protect cucumbers from Denver's intense UV radiation?

Use 30% shade cloth during heat waves above 95°F (35°C) and ensure plants have adequate moisture to cope with UV stress. Choose varieties with dense foliage like Cucumis sativus 'Marketmore 76' that provide natural fruit protection, and avoid reflective mulches that increase UV exposure.

What's the best way to water cucumbers in Denver's dry climate?

Deep water twice weekly rather than frequent shallow watering, applying 1-1.5 inches (2.5-4 cm) total per week. Use soaker hoses to deliver water directly to root zones and reduce evaporation. Water early morning to minimize loss to Denver's low humidity and constant wind.

Can I succession plant cucumbers in Denver's short season?

Limited succession planting is possible in Denver, but timing is critical. Plant your main crop in mid-May, then a second smaller planting by June 1. Later plantings rarely have time to mature before October frost, so focus on maximizing your early plantings instead.

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Tagged with

#Denver gardening #cucumber planting #Zone 5a #Colorado vegetables #frost protection #high altitude gardening #short season crops #cucumber varieties #vegetable timing #mountain gardening

Written By

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.