If you’re wondering when to plant lettuce in Colorado, timing is everything for a crisp, productive harvest. The state’s unique climate, with its short springs, hot summers, and sudden frosts, makes scheduleing your lettuce plantings a key skill.
Lettuce is a cool-season crop that thrives in the mild temperatures of spring and fall. In Colorado, you can often get two separate growing seasons for lettuce if you plan correctly. This guide will walk you through the best planting times for your specific area and how to extend your harvest window.
When to Plant Lettuce in Colorado – Best Planting Times for
The best planting times for lettuce in Colorado are primarily driven by your last spring frost and first fall frost dates. Because the state has such varied elevations and microclimates, these dates can shift significantly from one garden to the next.
Understanding Colorado’s Growing Zones
Colorado ranges from USDA Hardiness Zones 3b to 7a. Your zone dictates your frost-free window. You can find your zone by using the USDA’s online map with your zip code.
- Front Range (Zones 5b-6a): Last spring frost is typically around May 5-15. First fall frost is around October 5-15.
- Western Slope (Zones 6a-7a): A longer, warmer season. Last spring frost can be as early as late April. First fall frost often waits until mid-to-late October.
- High Mountain Valleys (Zones 3b-5a): A much shorter season. Last spring frost may not occur until early June, with fall frosts arriving in early September.
Spring Planting Schedule
For a spring harvest, you can plant lettuce seeds as soon as the soil is workable. This means it’s not frozen and is dry enough to crumble in your hand.
- Direct Seed Outdoors: Sow seeds 2-4 weeks before your average last frost date. For many along the Front Range, this is mid-April.
- Transplanting Seedlings: You can start seeds indoors 4-6 weeks before your last frost. Harden off seedlings and transplant them outside 2-3 weeks before the last frost.
- Succession Planting: Don’t plant all your seeds at once. Sow a new, small row every 10-14 days to ensure a continuous harvest into early summer.
Fall Planting Schedule
Fall is often the best time for growing lettuce in Colorado, as the cooling temperatures create perfect conditions. The key is to work backward from your first fall frost.
- Direct Seed for Fall: Calculate your planting date by finding your first frost date, then subtracting the “days to maturity” on your seed packet plus about 10 days for slower growth in cooler weather. For many areas, late July to mid-August is ideal.
- Transplanting for Fall: Start seeds indoors in mid-summer when it’s too hot to sow outside. Transplant the seedlings into the garden in late August or early September as temperatures begin to cool.
Using Season Extension Tools
Cold frames, row covers, and hoop houses are invaluable in Colorado. They can protect early spring plantings from late snows and extend your fall harvest by several weeks, sometimes even into winter.
Step-by-Step Planting Guide
Follow these steps for a successful lettuce crop.
- Choose Your Varieties: Select a mix for resilience. Loose-leaf and romaine types often handle temperature swings better than some crisphead varieties. Good choices include ‘Black Seeded Simpson’, ‘Buttercrunch’, and ‘Winter Density’.
- Prepare the Soil: Lettuce needs well-draining soil rich in organic matter. Work in 2-3 inches of compost before planting. The soil pH should be between 6.0 and 7.0.
- Plant Correctly: Sow seeds only 1/4 inch deep. Space them according to packet instructions, usually 1 inch apart, thinning later. For transplants, space them 6-12 inches apart.
- Water Wisely: Keep the soil consistently moist but not soggy. Use a light mulch of straw or grass clippings to retain moisture and keep soil cool. Drip irrigation is best to avoid wetting the foliage, which can promote disease.
- Provide Shade in Summer: For late spring or summer plantings, use a 30-50% shade cloth to protect young plants from intense sun and prevent bolting (premature flowering).
Common Challenges and Solutions
Colorado gardeners face a few specific hurdles with lettuce.
- Bolting: Lettuce bolts when temperatures rise above 75°F. To combat this, plant heat-tolerant varieties, use shade cloth, and focus on spring/fall planting windows.
- Frost Damage: Young lettuce can handle a light frost, but a hard freeze (below 28°F) will damage it. Always be prepared to cover plants with frost cloth or buckets on cold nights.
- Pests: Watch for aphids and slugs. A strong spray of water can dislodge aphids. For slugs, use diatomaceous earth or iron phosphate baits.
Harvesting Your Lettuce
You can begin harvesting leaf lettuce as soon as leaves are large enough to eat. For head lettuce, wait until the head feels firm. The best time to harvest is in the cool morning. For a “cut-and-come-again” approach, use scissors to cut leaves about an inch above the soil; the plant will often regrow for a second harvest.
FAQ: Lettuce Planting in Colorado
Can I grow lettuce in Colorado in the winter?
Yes, with protection! In a well-insulated cold frame or greenhouse, cold-hardy varieties like ‘Winter Density’ or ‘Arctic King’ can survive and provide harvests through much of the winter.
What is the latest I can plant lettuce in Colorado?
For a fall crop, your latest planting date depends on your first frost and if you use protection. Without protection, aim to have mature heads at least a week before your first frost. With a cold frame, you can plant 6-8 weeks before the first hard freeze.
Why did my lettuce seeds not germinate?
Lettuce seeds need cool soil (ideal is 55-65°F) and light to germinate. If you planted them too deep or if soil temperatures were to high, germination will be poor. Summer heat often causes dormancy.
Can I grow lettuce in containers on my Colorado patio?
Absolutely. Container gardening is a great option. Ensure the pot is at least 6-8 inches deep, has drainage holes, and is placed where it gets morning sun but some afternoon shade during the hottest months.
By following these timing guidelines and tips, you can enjoy fresh, homegrown lettuce from your Colorado garden for much of the year. Paying close attention to your local frost dates and being ready to protect your plants are the most important skills you can develop. With a little practice, you’ll have a reliable supply of crisp greens right from your backyard.