Washington · zones 6b–9a
When to plant tomatoes in Washington.
Sow or transplant between Apr 21 to Jun 21 in a typical year, keyed to Washington's median last frost around Apr 14. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Tomatoes dates for a typical Washington season.
1 · Start indoors
Mar 10 to May 10
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Apr 21 to Jun 21
Keyed to the ~Apr 14 last frost. Sow 0.25" deep, 24" apart.
Harvest
~73 days later
~12 lb per plant over ~8 weeks.
Washington spans more than one climate: Zone 8 is the most common zone, but the state runs 6b to 9a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Washington growing notes
West-side tomatoes race blight on a 60-day clock.
Cool nights and short varieties on the wet side of the mountains
Puget Sound summer nights commonly stay cool enough that a full-season slicer, roughly 73 days from transplant, still fails to ripen a real crop on schedule. The west-side problem is not raw season length, since 73 days fits the calendar easily; it is that tomato pollen loses viability once nights stay consistently cool, so fruit set slips week after week and every delayed fruit ripens deeper into blight weather. Growers on the wet side of the state do better picking a short-season variety built to finish in roughly 60 days, which sets and colors earlier, rather than fighting the marine climate with a slicer bred for a hotter summer.
East of the mountains, the Columbia Basin's hot, dry, irrigated summer is close to ideal tomato weather, and a full-season slicer finishes reliably there with room to spare in most years; growers on that side of the state can plant the classic beefsteak types west-side gardeners have to avoid, since the daytime heat and warm nights a slicer needs are simply available east of the Cascades in a way they are not on the coast.
Late blight is a west-side disease first
Late blight needs cool, humid conditions to spread, and Puget Sound's marine climate hands the disease exactly that for a much larger share of the growing season than the dry Columbia Basin ever does; a west-side tomato patch that gets regular rain and morning dew through summer carries real, ongoing blight pressure that an east-side planting on controlled drip irrigation mostly sidesteps. Watch for dark, greasy-looking patches on leaves and stems; once conditions turn favorable, the disease can move through a humid west-side planting fast enough to visibly worsen from one morning check to the next.
Staking or caging every plant to keep the canopy open, and watering at the base rather than overhead, matters more on the west side for exactly this reason, since anything that shortens how long leaves stay wet after rain or watering slows blight's spread. East-side growers dealing mostly with early blight instead, the slower-moving disease that favors the lowest, oldest leaves, can afford a more relaxed watering routine without inviting the same fast-moving risk.
Hornworms show up on both sides, on different schedules
Tomato hornworm feeds on both sides of the state, but the large green caterpillar tends to appear later in the season on the cooler west side, tracking the insect's own slower development in marine-climate temperatures, while Columbia Basin hornworms can reach damaging size earlier in a hot summer. Either way, the tell is the same: ragged holes in upper leaves and dark, pellet-like droppings on the leaves and ground below the feeding site, easier to spot than the well-camouflaged caterpillar itself.
A weekly check of a handful of plants, looking specifically for that dropping pattern rather than scanning for the caterpillar directly, catches an infestation early enough to hand-pick it off before a west-side plant, already working with a short season and a short-variety's smaller root system, loses leaf cover it cannot afford to spare during its compressed ripening window.
In Washington: watch for
The pests that find tomatoes here.
A middle-length season, about 187 frost-free days, means tomato, slicing overlaps tomato hornworm for a stretch each summer. Check plants every week or two and treat early.
Big green caterpillars strip leaves and leave black droppings.
Organic fix: Handpick at dusk; spray Bt on the young ones.
Clusters on new growth, sticky leaves, curling tips.
Organic fix: Blast with water, then insecticidal soap or neem.
Dark spots with concentric rings, starting on the lowest, oldest leaves.
Organic fix: Remove affected leaves, mulch to stop soil splash, space for airflow.
Greasy, water-soaked blotches in cool, wet spells. No rings, and not bottom-up.
Organic fix: Pull infected plants fast, keep leaves dry, use neem as a preventive.
Septoria leaf spot
Many small tan spots with dark brown edges, low leaves first, no rings inside.
Organic fix: Strip the lowest leaves, mulch against soil splash, stake for airflow.
Your season math: Washington gives tomatoes about 187 frost-free days, and it needs roughly 73 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting tomatoes in Washington: questions
When should I plant tomatoes in Washington?+
In a typical Washington year, sow tomatoes or set out transplants between Apr 21 to Jun 21, keyed to the state's median last frost around Apr 14. Your exact dates shift with your ZIP code and microclimate.
When do I start tomatoes seeds indoors in Washington?+
Start seeds inside about 6 weeks before set-out: roughly Mar 10 to May 10 for a typical Washington season.
What USDA zone is Washington?+
Washington spans zones 6b–9a, mostly zone 8. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many tomatoes plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.