When Do You Plant Tomatoes In Washington State

If you’re planning your garden in the Pacific Northwest, one of the first questions you’ll ask is when do you plant tomatoes in washington state. Getting the timing right is the single most important step for a successful harvest, as our unique climate presents both opportunities and challenges.

This guide will walk you through the best dates, varieties, and techniques to grow thriving tomatoes in Washington.

The short answer is: wait until after the last spring frost. Planting too early is the most common mistake. Cold soil and air stunt growth and make plants vulnerable to disease.

For most of Washington’s populated areas west of the Cascades, the safe planting window is from mid-May through early June. East of the Cascades, where springs are sunnier but frosts linger, aim for late May to early June. Always check your local frost dates as a starting point.

Understanding Washington’s Climate Zones

Washington isn’t just one climate. It’s essential to know your zone.

Western Washington (Maritime Climate): Mild, wet springs and summers. The last frost typically occurs between April 15th and May 15th. The challenge here is often cool soil and lack of heat, not late frosts.
Eastern Washington (Continental Climate): Hot, dry summers but colder winters and later springs. The last frost can be as late as mid-May. The challenge is a shorter growing season but with intense summer sun.
Microclimates: Urban Seattle gardens warm faster than rural Puyallup valleys. South-facing slopes gain heat quicker. Observe your own garden’s conditions.

Key Planting Dates by Region

These are general guidelines. You should always monitor the 10-day weather forcast before planting.

Puget Sound & Coastal Areas: May 15 – June 1
Willamette Valley (SW WA): May 10 – May 25
Columbia Basin & Yakima Valley: May 20 – June 5
Spokane & Northeastern WA: May 25 – June 10

Starting Seeds Indoors vs. Buying Transplants

Because of our long springs, most gardeners start with transplants. You can buy them or start seeds yourself.

Starting Seeds Indoors:

Begin seeds 6-8 weeks before your planned outdoor planting date. For a May 20th planting, start seeds around late March.
Use a seed-starting mix and provide plenty of light. A sunny window is often insufficient; consider grow lights.
Harden off seedlings for 7-10 days before planting. This means gradually exposing them to outdoor conditions for a few more hours each day.

Choosing Healthy Transplants:

Look for stocky, dark green plants. Avoid those that are already flowering or have yellowing leaves.
Check the roots—they should be white and firm, not brown or circling densely at the bottom of the pot.

Preparing Your Garden Soil

Tomatoes need warm, well-drained, and nutrient-rich soil. Washington’s heavy clay soils, especially in the west, need ammendment.

Test Your Soil: A simple test can reveal pH and nutrient levels. Tomatoes prefer slightly acidic soil (pH 6.2-6.8).
Amend with Compost: Mix in 2-4 inches of well-rotted compost or aged manure. This improves drainage in clay and water retention in sandy soils.
Warm the Soil: Use black plastic mulch or landscape fabric laid over the bed for 1-2 weeks before planting. This raises soil temperature by several critical degrees.

The Best Tomato Varieties for Washington

Choosing varieties suited to cooler summers and shorter seasons is key. Look for terms like “early season,” “cold-tolerant,” or “short season.”

Early Girls: A classic for a reason. Produces fruit in about 50 days, ideal for our summers.
Oregon Spring: Sets fruit in cool weather and is very disease resistant.
Sungold: A super-sweet cherry tomato that reliably ripens even in cooler years.
San Marzano: A paste tomato that does surprisingly well in Eastern WA’s heat.
Stupice: An early, prolific Czech variety that thrives in the Pacific Northwest.

Step-by-Step Planting Guide

When your soil is warm (at least 55°F) and frost danger has passed, you’re ready.

Dig a Deep Hole: Bury the stem. Tomatoes develop roots all along their buried stems, creating a stronger plant.
Amend the Hole: Add a handful of balanced organic fertilizer or a specific tomato food to the planting hole, mixing it with the native soil.
Plant Deep: Remove the lower leaves and place the plant so only the top few sets of leaves are above ground. If the plant is leggy, you can trench it sideways in a shallow trench.
Water Thoroughly: Water deeply at the base to settle the soil and eliminate air pockets.
Add Support: Place a tall cage or stake at planting time to avoid damaging roots later.
Apply Mulch: After planting, apply 2-3 inches of straw or shredded bark mulch to retain moisture and suppress weeds. Wait until after the soil is warm to apply mulch.

Protecting Your Young Plants

Washington’s spring weather can be unpredictable. Have protection ready.

Frost Protection: Keep row covers, cloches, or even old bedsheets handy to drape over plants if a late frost is predicted.
Cold Frames/Walls of Water: These are excellent for getting a 2-3 week head start on the season, especially in cooler areas.

Common Washington Tomato Challenges

Our damp climate fosters certain diseases. Prevention is your best tool.

Late Blight: A devastating fungus. Prevent by choosing resistant varieties, spacing plants for air flow, and watering at the soil level (not the leaves).
Blossom End Rot: Caused by calcium deficiency and irregular watering. Keep soil consistently moist and ensure proper pH.
Poor Fruit Set: Cool nighttime temperatures (below 55°F) can cause flowers to drop. Using varieties bred for cool climates helps alot.
Slugs and Snails: A major pest in Western WA. Use beer traps, copper tape, or iron phosphate bait.

Seasonal Care for a Bountiful Harvest

Consistent care through the summer leads to the best flavor.

Watering: Water deeply 1-2 times per week, depending on heat. Inconsistent watering leads to cracked fruit.
Fertilizing: Feed with a balanced fertilizer at planting, then switch to a lower-nitrogen, higher-potassium fertilizer when flowering begins to promote fruit.
Pruning: For indeterminate varieties, prune “suckers” (the shoots that form in leaf joints) to improve air flow and direct energy to fruit. Determinate varieties need little pruning.
Harvesting: Pick tomatoes when they are fully colored and slightly soft to the touch. If frost threatens in early fall, you can harvest mature green tomatoes to ripen indoors.

FAQ: Planting Tomatoes in Washington State

What is the absolute last date to plant tomatoes in Washington?

For a fall harvest, you can plant fast-maturing cherry tomato varieties as late as early July. For full-sized tomatoes, planting after mid-June is risky, as they may not ripen before fall coolness and rain arrives.

Can I plant tomatoes in May in Washington?

Yes, late May is generally the ideal and safest time for planting tomatoes across much of the state. Always verify that nighttime temperatures are reliably above 50°F.

How do I get tomatoes to ripen in Western Washington’s cool summers?

Choose early varieties, plant in the sunniest, most sheltered spot you have (against a south-facing wall is perfect), and use black plastic mulch to retain heat. Prune excess foliage to let sun reach the fruit.

Should I use tomato cages in Washington?

Yes, strong supports are highly recommended. Our wet weather can cause sprawling plants to develop fungal diseases from contact with damp soil. Cages keep fruit clean and improve air circulation.

What if my soil is very heavy clay?

Raised beds are an excellent solution for improving drainage and warming soil faster in the spring. Amending with generous amounts of compost is also essential for clay soils.