Washington State tomato growers aim for soil temperatures near sixty degrees, usually by mid-May. Knowing When To Plant Tomatoes In Washington State is the key to a successful harvest, as our cool springs and variable weather can easily damage young plants. This guide covers everything you need to time your planting perfectly, from soil prep to frost dates.
Tomatoes love warmth. They stop growing when soil drops below 50°F. In Washington, that means waiting until the ground has fully warmed up. Planting too early leads to stunted plants and poor yields.
Understanding Washington’s Climate Zones
Washington is not one-size-fits-all for tomatoes. The state splits into three main climate zones. Each zone has its own ideal planting window.
Western Washington (West Of The Cascades)
This area includes Seattle, Tacoma, and Olympia. It has mild, wet springs. Soil warms slowly here. The last frost usually happens between mid-March and mid-April. But the ground stays cool for weeks after.
For Western Washington, aim to plant tomatoes between May 1st and May 15th. Some gardeners wait until late May for warmer soil. Use black plastic or row covers to heat the soil faster.
Eastern Washington (East Of The Cascades)
Spokane, Yakima, and the Tri-Cities have hotter summers but colder springs. Frost can hit as late as early May. Soil warms quickly once the sun comes out.
Plant tomatoes here from May 10th to May 25th. Watch the forecast for late frosts. A sudden cold snap can kill unprotected plants.
Higher Elevations And Mountain Areas
Places like Leavenworth, Winthrop, or the Olympic Peninsula foothills have short growing seasons. Frost can occur into June. Soil temps stay low longer.
For these areas, wait until late May or early June. Use season extenders like cloches or cold frames. Choose early-maturing tomato varieties to beat the first fall frost.
When To Plant Tomatoes In Washington State
This heading sums up the core timing rule. For most of Washington, the safe window is mid-May to early June. But you need to check two things before planting: soil temperature and frost risk.
Checking Soil Temperature
Tomatoes need soil at least 60°F for strong root growth. At 50°F, roots barely grow. Use a soil thermometer to check. Insert it 4 inches deep in the morning.
- If soil is below 55°F, wait. It will warm up in a week or two.
- If soil is 60°F or above, you can plant.
- Black plastic mulch can raise soil temps by 5-10°F.
Watching The Last Frost Date
Tomatoes die if exposed to frost. Know your area’s average last frost date. For Seattle, it’s around March 25th. For Spokane, it’s May 5th. But these are averages. A late frost can happen.
Wait at least two weeks after the last frost date to plant. This gives the soil time to warm. If a cold night is forecast, cover your plants with fabric or a bucket.
Preparing Your Garden For Tomatoes
Good prep makes planting easier. Start working on your soil a few weeks before you plant. This gives amendments time to blend in.
Choosing The Right Spot
Tomatoes need full sun. Pick a spot that gets at least 8 hours of direct sunlight daily. Avoid low areas where cold air settles. Raised beds warm up faster than ground soil.
Amending The Soil
Washington soil varies from clay to sandy loam. Add compost or aged manure to improve drainage and nutrients. Work it in 6-8 inches deep. A balanced fertilizer (like 10-10-10) helps young plants.
- Test your soil pH. Tomatoes prefer 6.0 to 6.8.
- Add lime if soil is too acidic (common in Western WA).
- Add sulfur if soil is too alkaline (rare in WA).
Hardening Off Seedlings
If you started seeds indoors or bought transplants, they need to adjust to outdoor conditions. This process takes 7-10 days. Start about two weeks before your planned planting date.
- Place seedlings outside in a shady spot for 1 hour on day one.
- Increase time by 1-2 hours each day.
- Gradually move them into more sun.
- Leave them out overnight after 5-7 days, if temps stay above 50°F.
- Plant after they’ve spent 24 hours outside for 2-3 days.
Step-By-Step Planting Guide
Once the soil is warm and seedlings are hardened off, it’s time to plant. Follow these steps for strong, healthy tomatoes.
Digging The Hole
Dig a hole deeper than the pot. Tomatoes can grow roots along their stems. Bury the stem up to the first set of true leaves. This creates a stronger root system.
Space plants 18-24 inches apart for determinate varieties. Indeterminate types need 24-36 inches. Give them room to grow without crowding.
Adding Support
Put cages or stakes in at planting time. This avoids damaging roots later. Use sturdy cages for large varieties. Stake tall indeterminates with 6-foot poles.
Watering And Mulching
Water deeply right after planting. This settles the soil around roots. Add a 2-3 inch layer of mulch around plants. Straw, grass clippings, or shredded leaves work well. Mulch keeps soil warm and reduces weeds.
Best Tomato Varieties For Washington
Not all tomatoes thrive in Washington’s climate. Choose varieties that mature quickly and handle cool weather. Here are top picks for each region.
Early Maturing Varieties (50-65 Days)
- Stupice – 55 days, great flavor, handles cool temps.
- Oregon Spring – 58 days, sets fruit in cool weather.
- Sub Arctic Plenty – 50 days, very early, small fruit.
- Glacier – 55 days, cold-tolerant, sweet taste.
Main Season Varieties (65-80 Days)
- Early Girl – 62 days, reliable, good for slicing.
- Celebrity – 70 days, disease-resistant, heavy yields.
- Better Boy – 75 days, large fruit, classic flavor.
- San Marzano – 78 days, paste tomato, great for sauces.
Cherry And Small Varieties
- Sweet 100 – 65 days, prolific, very sweet.
- Sun Gold – 57 days, orange, candy-like flavor.
- Yellow Pear – 70 days, mild, fun shape.
- Black Cherry – 75 days, rich, complex taste.
Common Planting Mistakes In Washington
Even experienced gardeners make errors. Avoid these pitfalls to get a better harvest.
Planting Too Early
This is the number one mistake. Warm days tempt you to plant in April. But cold soil stunts growth. Plants may survive but never produce well. Wait for consistent soil temps above 60°F.
Overwatering
Washington’s spring rains can keep soil wet. Overwatering leads to root rot and fungal diseases. Water only when the top inch of soil feels dry. Use drip irrigation to keep leaves dry.
Ignoring Wind Protection
Wind can dry out plants and break stems. Use windbreaks like fences or tall plants. Stake tomatoes securely. In exposed areas, plant in a sheltered spot.
Not Using Season Extenders
Washington’s cool nights slow tomato growth. Use row covers, cloches, or wall o’ water to trap heat. Remove covers during the day if temps rise above 85°F. This can add weeks to your growing season.
Extending The Growing Season
Washington’s summer can be short. Use these tricks to get ripe tomatoes before frost.
Using Black Plastic Mulch
Black plastic absorbs heat and warms soil. Lay it down 2-3 weeks before planting. Cut holes for plants. This can raise soil temps by 5°F. It also suppresses weeds.
Building A Cold Frame
A cold frame is a box with a glass or plastic lid. It traps heat and protects plants from cold. Place it over your tomato bed. Open the lid on warm days to prevent overheating.
Choosing Determinate Varieties
Determinate tomatoes grow to a fixed size and ripen all at once. They mature faster than indeterminate types. For short seasons, pick determinate varieties like Roma or Bush Early Girl.
Frequently Asked Questions
Can I Plant Tomatoes In Washington In April?
Only in very warm microclimates or with heavy protection. Most of Washington’s soil is too cold in April. Wait until May for best results. If you try April, use cloches and watch for frost.
What Is The Best Month To Plant Tomatoes In Washington?
May is the best month. Early May for Western Washington, mid-to-late May for Eastern Washington. Higher elevations may need early June. Always check soil temperature first.
How Do I Protect Tomato Plants From Late Frost?
Cover plants with fabric, blankets, or plastic sheeting. Use stakes to keep covers off leaves. Remove covers in the morning. Wall o’ water or cloches give extra protection.
Should I Start Tomatoes Indoors In Washington?
Yes. Starting seeds indoors 6-8 weeks before planting gives you a head start. Use grow lights or a sunny window. Harden off seedlings before moving them outside.
What Tomato Varieties Grow Best In Cool Washington Summers?
Early varieties like Stupice, Oregon Spring, and Glacier do well. Cherry tomatoes like Sun Gold and Sweet 100 are also reliable. Avoid long-season beefsteak types unless you have a greenhouse.
Final Tips For Washington Tomato Growers
Planting at the right time is half the battle. The other half is care. Water deeply but infrequently. Fertilize every 2-3 weeks with a balanced fertilizer. Prune suckers from indeterminate plants to improve air flow.
Watch for common pests like aphids and hornworms. Use insecticidal soap or hand-pick pests. Rotate your tomato spot each year to prevent soil-borne diseases.
With proper timing and care, you can enjoy fresh tomatoes from August until the first frost. Many Washington gardeners harvest into October with a little luck. Start planning now, and your plants will reward you.
Remember, the exact date varies each year. Use a soil thermometer and watch the forecast. When soil hits 60°F and frost is no longer a threat, it’s time to plant. That’s the simple rule for When To Plant Tomatoes In Washington State.