Planting Guides
When to Plant Tomatoes in Seattle: Complete Guide + Best Varieties for Zone 8b
Seattle, Washington
USDA Zone 8b
Last Frost: Mar 15
Last updated: December 4, 2025
Learn when to plant tomatoes in Seattle with specific dates for Zone 8b. Compare 6 varieties & discover which grow best in Pacific Northwest climate.
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Quick Answer
Start tomato seeds indoors February 15-March 1. Transplant outdoors April 15-May 15 after March 14 last frost.
TL;DR
Plant tomatoes in Seattle from mid-April through May 15 after last frost (March 14). Start seeds indoors February 15-March 1, transplant outdoors April 15-May 15. Best varieties for Zone 8b include 'Stupice' and 'Early Girl' for cool-weather tolerance, plus 'Surefire Red' bred specifically for Pacific Northwest conditions.
Frequently Asked Questions
What are the best tomato varieties for Seattle's cool summers?
Solanum lycopersicum 'Stupice', Solanum lycopersicum 'Early Girl', and Solanum lycopersicum 'Surefire Red' consistently outperform other varieties in Seattle's Zone 8b climate. These varieties set fruit in cool temperatures (40-50°F nights) and ripen quickly during our brief warm periods. Avoid heat-loving varieties like 'Cherokee Purple' or 'Brandywine' unless you have a very warm, protected microclimate.
When is it too late to plant tomatoes in Seattle?
June 1st is generally the cutoff for planting tomatoes in Seattle. Determinate varieties and ultra-early types like Solanum lycopersicum 'Stupice' can still produce if planted by mid-June, but longer-season varieties won't have time to mature before fall rains increase disease pressure.
How do I protect tomatoes from Seattle's late blight?
Choose resistant varieties like Solanum lycopersicum 'Legend' as your primary defense. Maintain excellent air circulation through aggressive pruning and proper plant spacing. Remove lower leaves that touch soil, and avoid overhead watering. At first sign of dark, water-soaked leaf spots, remove affected foliage immediately and apply copper fungicide during wet weather periods.
Should I use row covers in Seattle's cool springs?
Yes, row covers or Wall O' Water protections significantly improve early-season growth in Seattle. Our March-May weather can include unexpected cold snaps that stunt unprotected plants. Remove covers once daytime temperatures consistently reach 70°F and nighttime temperatures stay above 55°F.
What soil amendments work best for Seattle tomatoes?
Seattle's clay-heavy, acidic soil benefits from adding compost (1/3 of total volume) and drainage amendments like perlite or coarse sand. Test soil pH—most Seattle soils are naturally in the optimal 6.0-6.8 range for tomatoes. Add phosphorus at planting time, as our heavy winter rains leach this crucial nutrient.
How do I ripen green tomatoes indoors in Seattle?
Harvest mature green tomatoes (full size but not colored) before first frost. Place in paper bags with ripe apples or bananas—the ethylene gas speeds ripening. Store at room temperature and check daily. For longer storage, wrap individual tomatoes in newspaper and keep in a cool (55-60°F / 13-16°C) location where they'll ripen gradually over 4-6 weeks.
Can I grow determinate tomatoes in containers in Seattle?
Absolutely—determinate varieties like Solanum lycopersicum 'Oregon Spring' are perfect for Seattle container growing. Use containers at least 20 gallons for full-size plants, or 10-15 gallons for compact determinates. Container growing allows you to move plants to protected areas during cool spells and provides better drainage than Seattle's heavy native soils.
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M
Mike Thompson
Mike's been designing residential landscapes in the Seattle area, with a particular focus on Pacific Northwest natives and sustainable practices. He's a Washington State Master Gardener and worked in construction before landscaping, which gives him a practical edge when it comes to building raised beds and hardscaping projects. He runs a small side business propagating and selling unusual perennials at farmers markets on weekends. His property serves as a testing ground for low-maintenance, wildlife-friendly garden designs. Mike's philosophy: if it requires weekly maintenance, it's not sustainable.
