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.

DDorothy "Dot" Williams

December 4, 2025

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When to plant tomatoes in Seattle - healthy seedlings ready for Zone 8b transplanting — — Image © PlantReference.org 2025

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.

Product Recommendations

Wall O' Water Plant Protectors

($15-25)— Essential for Seattle's unpredictable spring weather

Wall O' Water Plant Protectors Set of 3

https://www.amazon.com/Wall-Water-Plant-Protector-Pack/dp/B000BQUFVQ

Clear water-filled tubes create a protective microclimate around young tomato transplants, warming air temperature by 10-15°F. Essential for Seattle's cool, unpredictable spring weather. Each protector holds 3 gallons of water that releases heat at night. Allows planting 2-3 weeks earlier than unprotected plants. Reusable for multiple seasons. Easy setup—just fill with water and place around transplants. Perfect insurance against Seattle's late cold snaps that can stunt or kill unprotected tomatoes.

Price: $15.99-$24.99

XLUX Soil Moisture Meter

($10-15)— Monitor Seattle's variable soil moisture levels

XLUX Soil Moisture Meter T10 Bonsai Care Set

https://www.amazon.com/XLUX-T10-Moisture-Sensor-Meter/dp/B014MJ8J2U

10-inch probe reaches deep into Seattle's clay soils to measure moisture at root zone level. No batteries required—simply push into soil for instant reading. Essential for managing irrigation in Seattle's variable climate where surface soil appears dry while roots sit in waterlogged conditions. Prevents both overwatering and underwatering that affect tomatoes in Pacific Northwest gardens. Durable construction withstands repeated use in multiple garden locations. Particularly valuable for container growers who need precise moisture management.

Price: $10.99-$14.99

Dr. Earth Premium Gold All Purpose Fertilizer

($12-18)— Organic nutrition for Seattle's leached soils

Dr. Earth Premium Gold All Purpose Fertilizer 4 lb

https://www.amazon.com/Dr-Earth-Premium-Purpose-Fertilizer/dp/B002LZQHFK

Organic 4-4-4 blend provides balanced nutrition ideal for Seattle's nutrient-leached soils. Contains beneficial soil microbes and mycorrhizae that improve nutrient uptake in cool, clay-heavy Pacific Northwest soils. TruBiotic formula feeds plants and soil organisms. Perfect for Seattle gardeners transitioning from conventional fertilizers. Safe around children and pets. Apply at planting and monthly throughout growing season. Particularly effective for tomatoes in raised beds and containers where soil amendments are needed. Long-lasting granular formula releases nutrients slowly.

Price: $12.49-$17.99

Premium Cedar Mulch

($8-12)— Pacific Northwest disease prevention

Premium Cedar Mulch 2 Cubic Foot Bags

https://www.homedepot.com/p/Premium-Cedar-Mulch-2-cu-ft-CEDMULCH/206313163

Locally-sourced cedar mulch naturally resists fungal diseases common in Seattle's humid climate. Cedar's natural oils provide antifungal properties that help prevent soil-borne diseases like early blight and late blight. Excellent moisture retention during Seattle's occasional summer dry spells while preventing soil splash during heavy Pacific Northwest rains. Breaks down slowly, providing long-term soil improvement. Attractive reddish-brown color complements Seattle garden aesthetics. Apply 3-4 inch layer around tomato plants after soil warms in late May.

Price: $8.99-$11.99

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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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."