Washington · zones 6b–9a
When to plant potatoes in Washington.
Sow between Mar 7 to Apr 9 in a typical year, keyed to Washington's median last frost around Apr 14. A second, fall sowing fits Jun 30 to Jul 13. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Potatoes dates for a typical Washington season.
Direct sow
Mar 7 to Apr 9
Keyed to the ~Apr 14 last frost. Sow 4" deep, 12" apart.
Fall round
Jun 30 to Jul 13
Counted back from the ~Oct 18 first frost.
Harvest
~90 days later
~3 lb per plant over ~1 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
Washington splits potatoes into a scab problem and a blight problem.
Basin soil favors scab, west-side soil suppresses it
Common scab shows up as rough, corky patches marking a potato's skin without touching the flesh underneath, and the disease is naturally held down in acidic soil, at a pH of 5.2 or below; the two halves of Washington sit on opposite sides of that line for very different reasons. Puget Sound's naturally acidic, conifer-forest-derived soils on the west side tend to suppress scab on their own, while much of the irrigated Columbia Basin runs closer to neutral or mildly alkaline, closer to the range where scab shows up more freely on the same variety.
A Columbia Basin grower fighting scab does better leaning on a variety with real field-proven tolerance, Russet Burbank among them, than trying to acidify garden-scale soil, since bred-in resistance solves more of the problem than a soil amendment realistically can at that scale. A west-side grower generally does not need to think about scab at all and can pick varieties purely on flavor and storage instead.
Blight runs the opposite direction
Late blight thrives in the cool, humid conditions Puget Sound delivers for much of the growing season, and a west-side potato patch that gets rained on regularly through summer carries real blight risk that a Columbia Basin planting, watered on a controlled irrigation schedule in dry air, mostly avoids. Watch for dark, water-soaked patches on leaves that spread fast in wet weather, since blight can move through a damp west-side row within days once conditions turn favorable.
Hilling soil around the stems, done everywhere for tuber cover, does double duty on the west side by shedding rain away from the base of the plant rather than letting it pool, and spacing rows for airflow matters more there too, since a crowded, still-air planting holds humidity around the leaves longer after every rain. East-side growers can plant closer without the same blight consequence, though tight spacing still costs tuber size regardless of region.
A beetle and an irrigation habit both sides share
Colorado potato beetle overwinters in garden soil statewide and emerges within days of the first sustained warm stretch wherever a garden sits; scouting for yellow-orange egg clusters on the underside of leaves as soon as plants emerge, rather than waiting for visible damage, catches the count before it climbs past the extension threshold of about 2 larvae per plant, averaged over a handful of plants checked at once, which is the point where hand-picking alone stops being enough.
Tuber sizing depends on steady moisture through the weeks after hilling regardless of which side of the mountains a garden sits on; Columbia Basin growers on a controlled irrigation schedule generally deliver that consistency more reliably than a west-side garden relying on rainfall alone, which can swing from a soaked week to a dry one depending entirely on the season's storm pattern.
In Washington: watch for
The pests that find potatoes here.
A middle-length season, about 187 frost-free days, means potato overlaps colorado potato beetle for a stretch each summer. Check plants every week or two and treat early.
Striped beetles and orange grubs eating the leaves.
Organic fix: Handpick adults, crush the orange egg clusters, dust with diatomaceous earth.
Dark greasy blotches after cool, wet spells.
Organic fix: Pull infected plants fast, keep leaves dry, use neem as a preventive.
Common scab
Rough, corky patches on the skin, raised on some tubers and sunk into pits on others.
Organic fix: Keep the bed evenly moist through the weeks right after tubers set, rotate away from potatoes, and pick a scab-resistant variety next time.
Your season math: Washington gives potatoes about 187 frost-free days, and it needs roughly 90 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting potatoes in Washington: questions
When should I plant potatoes in Washington?+
In a typical Washington year, sow potatoes between Mar 7 to Apr 9, keyed to the state's median last frost around Apr 14. There's also a fall window: Jun 30 to Jul 13. Your exact dates shift with your ZIP code and microclimate.
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 potatoes 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.