Planting Guides

When to Plant Lettuce 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 lettuce in Denver with specific dates for Zone 5a. Compare 6 varieties & discover which grow best in Colorado's climate.

DDorothy "Dot" Williams

October 30, 2025

Lettuce growing in Denver garden with Rocky Mountain backdrop showing best varieties for Zone 5a — — Image © PlantReference.org 2026

Quick Answer

Plant lettuce in Denver March 15-April 1 for spring harvest, August 1-15 for fall. Lactuca sativa 'Buttercrunch' handles Denver's conditions best.

TL;DR

Plant lettuce in Denver starting March 15-April 1 for spring harvest, with fall plantings from August 1-15. Zone 5a's 148-day growing season allows two productive seasons. Lactuca sativa 'Buttercrunch' and Lactuca sativa 'Red Oak Leaf' offer best heat tolerance for Denver summers.

Frequently Asked Questions

When is the last date I can plant lettuce in Denver?

For fall harvest, plant quick-maturing varieties like mesclun mix by September 15 to ensure harvest before Denver's October 4 first frost. Lactuca sativa 'Red Oak Leaf' can be planted as late as September 1 for cut-and-come-again harvesting through early October.

Can lettuce survive Denver winters?

Most lettuce varieties cannot survive Denver's harsh winters outdoors, but cold frames or unheated greenhouses can extend the season. Lactuca sativa 'Winter Density' romaine can survive in protected environments with temperatures staying above 15°F (-9°C).

Why won't my lettuce seeds germinate in Denver's summer heat?

Lettuce seeds enter thermoinhibition when soil temperatures exceed 80°F (27°C), common in Denver summers. Pre-chill seeds in refrigerator for 24 hours before planting, or use the board method—cover seeded rows with wooden boards until germination begins.

How much water do lettuce plants need in Denver's dry climate?

Denver lettuce requires 1-1.5 inches weekly including rainfall. The low humidity increases water loss, so deep watering 2-3 times weekly works better than daily light watering. Monitor soil moisture at 2-inch depth.

Which lettuce grows best in Denver's alkaline soil?

Lactuca sativa 'Buttercrunch' and Lactuca sativa 'Red Oak Leaf' tolerate Denver's naturally alkaline soil (pH 7.5-8.0) better than other varieties. Adding compost annually and using chelated iron fertilizer helps all varieties perform better in alkaline conditions.

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Tagged with

#lettuce planting #Denver gardening #Zone 5a #Colorado vegetables #spring lettuce #fall lettuce #high altitude gardening #lettuce varieties #succession planting #frost protection

Written By

Dorothy "Dot" Williams

Dot grew up on a small farm in rural Virginia and has maintained a vegetable garden for decades. After retiring from teaching elementary school, she became a Master Gardener volunteer and spends her time mentoring new gardeners at community garden plots in Richmond. She's especially knowledgeable about heirloom varieties, seed saving, and traditional growing methods passed down from her grandmother. Dot's no-nonsense advice comes from extensive trial and error—she's seen every tomato disease, pest problem, and weather disaster imaginable. Her biggest pet peeve is gardeners who overcomplicate simple tasks. "Plants want to grow," she often says. "Your job is to not get in their way."