Planting Guides
When to Plant Lettuce in Seattle: Complete Guide + Best Varieties for Zone 8b
Seattle, Washington
USDA Zone 8b
Last Frost: Mar 15
Last updated: October 30, 2025
Learn when to plant lettuce in Seattle with specific dates for Zone 8b. Compare 6 varieties and discover why the Pacific Northwest's cool maritime climate makes Seattle arguably the best lettuce city in America with near year-round production potential.
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Quick Answer
Direct sow lettuce outdoors February 15-March 1 in Seattle. Seeds germinate in soil as cool as 40°F. Year-round production possible with winter cloches.
TL;DR
Direct sow lettuce outdoors February 15-March 1 or start seeds indoors February 1-15 for the earliest harvest. Seattle's 245-day frost-free season and cool maritime climate make it arguably the best lettuce city in America—temperatures rarely exceed 85°F, so the summer gap is only 3-4 weeks (shorter than any other major city). Production runs from February through December with winter growing under cloches. Lactuca sativa var. longifolia (Romaine) overwinters outdoors in Zone 8b. The primary challenge isn't heat—it's slugs and winter rain that require high tunnels for dry foliage.
Frequently Asked Questions
When is the best time to plant lettuce in Seattle?
Direct sow lettuce outdoors February 15-March 1—the earliest start of any major US city. Succession sow every 10-14 days from March through October for continuous production. For winter growing, establish plants by September 15 under cloches before declining day length limits growth. Seattle's cool maritime climate supports 15-20 succession plantings per year—the most of any US city—because temperatures rarely exceed the 85°F bolting threshold that creates mandatory summer gaps elsewhere.
What makes Seattle the best lettuce city in America?
Seattle's Puget Sound maritime climate delivers exactly what lettuce evolved for: mild temperatures (summer highs averaging 75-80°F), consistent moisture, and rare heat extremes. The summer gap when bolting temperatures arrive is only 3-4 weeks—the shortest of any major US city—and many years no meaningful gap occurs at all. All six major lettuce types produce successfully here, including heat-sensitive Iceberg and Bibb that most cities can only grow during narrow windows. Year-round production is feasible with simple cloches for winter rain protection.
How do I manage slugs in Seattle lettuce?
Slugs are Seattle's primary lettuce pest—far more damaging than in any other US region. The cool, moist Pacific Northwest climate creates ideal slug habitat year-round. Combine multiple methods: water in the morning so soil dries by evening, remove daytime hiding spots, apply iron phosphate bait (Sluggo) around plants, and install copper strips around raised bed edges. No single method eliminates Seattle's persistent slug pressure—the most effective strategy layers several approaches simultaneously throughout the growing season.
Can I grow lettuce year-round in Seattle?
Yes—Seattle is the only major US city where genuine year-round lettuce production is feasible with minimal infrastructure. Plants established by September 15 under simple cloches produce through winter, though growth slows significantly from December through January due to short day length (8.5 hours). Growth resumes vigorously in February as day length increases. Lactuca sativa var. longifolia (Romaine) overwinters outdoors in Zone 8b without protection in most years. The primary winter challenge is rain management to prevent downy mildew, not cold protection.
Why do I need cloches in mild Seattle?
Not for warmth—Seattle's mild Zone 8b winters provide adequate temperatures for lettuce survival. Cloches serve primarily as rain protection. The Pacific Northwest receives almost all of its 37 inches of annual rainfall from October through May, keeping lettuce foliage constantly wet during the active growing season. Wet foliage promotes downy mildew, basal rot, and creates the moist conditions that sustain Seattle's legendary slug populations. A simple cloche keeping rain off lettuce transforms winter growing from marginal to reliable.
How does Seattle compare to other West Coast cities for lettuce?
Seattle is superior to Portland (similar maritime climate but slightly warmer summers creating a marginally longer gap), San Francisco (fog creates near-identical conditions but with less rainfall to manage), and Los Angeles (too hot for consistent year-round lettuce without extensive shade). Seattle's unique advantage is the combination of cool enough for virtually no summer gap, warm enough for winter survival, and enough latitude to provide adequate day length for 10-11 months of active growth.
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Aisha Patel
Aisha manages a small tropical nursery on the east side of Houston, specializing in plants that can handle the Gulf Coast's humidity, heat, and unpredictable flooding. She studied horticulture in college and worked at a wholesale grower before opening her own operation. Growing up, her parents kept a kitchen garden with okra, bitter gourd, and curry leaf plants—a tradition she's continued. Houston's subtropical climate lets her grow things most of the country can't, but it also means dealing with fungal issues, standing water, and summers where it's too hot for even tomatoes. Aisha writes about tropical and subtropical plant care, humidity management, and working with heavy clay soils.
