Washington · zones 6b–9a
When to plant sweet corn in Washington.
Sow between Apr 21 to Jul 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
Sweet Corn dates for a typical Washington season.
Direct sow
Apr 21 to Jul 21
Keyed to the ~Apr 14 last frost. Sow 1.5" deep, 12" apart.
Harvest
~75 days later
~1 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
Corn finds its real home east of the Cascades in Washington.
Heat is the ingredient Puget Sound cannot supply
Sweet corn needs soil that holds at least 55 degrees at 2 inches deep to germinate reliably, with the optimum running 60 to 85 degrees, and warm nights through summer to fill ears out properly, conditions the irrigated Columbia Basin delivers about as well as anywhere in the state. Puget Sound's marine-cooled summers, by contrast, often leave corn germinating slowly and maturing later than the same variety would east of the mountains, even from an identical sowing date.
West-side growers do better choosing a shorter-season variety, something finishing well under 75 days, and warming the bed with black plastic mulch laid a couple of weeks ahead of sowing, which banks real soil heat the marine air will not otherwise provide. Waiting for a full week of steady warm soil readings, rather than one warm afternoon a Puget Sound cold front can erase within a day, avoids a patchy, uneven stand.
Wind carries pollen away from a thin row on either side
Corn relies on wind to move pollen from tassel to silk, and a single narrow row cannot hold onto enough of its own pollen to fertilize itself well, whether that wind is a dry gust off the Columbia Basin or a damper breeze coming off Puget Sound. The fix does not change with geography: shape the planting into a block running at least 4 rows across rather than a single long line, even if that means a shorter block in a tight garden, so enough pollen stays circulating within the stand itself to fill ears out fully.
Twelve rounds of successive plantings are realistic across a Washington season, spaced a couple of weeks apart, and Columbia Basin growers can push those rounds later into summer with confidence that heat will keep filling ears properly, while west-side growers do better clustering their rounds earlier in the season, before the cooling that comes with autumn's return of Puget Sound cloud cover slows ear development.
The earworm test works the same regardless of which side grows the corn
Corn earworm moths seek out silk that is still fresh to lay their eggs, and the larva that emerges bores straight down toward the ear tip well before any sign of trouble shows from outside the husk, on either side of the state. The countermeasure is timing rather than repetition: catch each ear at the point its own silk turns wilted and brown, a stretch that typically falls 3 to 7 days past when the silk first showed, and work a small dose of mineral oil over that silk to smother both eggs and newly hatched larvae while leaving the pollen underneath untouched.
Move that timing earlier, onto silk still green and fresh, and the oil itself becomes the problem, sealing off pollen before it can reach the kernels and leaving a hollow, toothless tip on an ear that was never actually infested; treat each ear once, based on its own silk, never on a fixed calendar date. European corn borer, the season's other named threat here, works inside the stalk instead of the ear, so a plant that goes down mid-season with no wind event behind it is the tell for that pest instead.
In Washington: watch for
The pests that find sweet corn here.
A middle-length season, about 187 frost-free days, means sweet corn overlaps corn earworm for a stretch each summer. Check plants every week or two and treat early.
Caterpillars feeding down in the tip of the ear.
Organic fix: A few drops of oil on the silk; Bt on the silks.
Clusters on the tassels and upper leaves.
Organic fix: Usually minor; insecticidal soap if heavy.
Fall armyworm
Ragged holes through the unfurling whorl leaves, with sawdust-like droppings down in the funnel.
Organic fix: Check whorls weekly before tassel; Bt or spinosad while the caterpillars are still small.
Cinnamon-brown powdery pustules breaking out on BOTH sides of the same leaf, lower leaves first, darkening as they age.
Organic fix: Water at the ground rather than overhead, and choose resistant varieties next season; sprays are rarely worth it.
Your season math: Washington gives sweet corn about 187 frost-free days, and it needs roughly 75 days to a first harvest. That fits about 12 re-sown rounds across the season, so you can keep it coming instead of picking once.
Planting sweet corn in Washington: questions
When should I plant sweet corn in Washington?+
In a typical Washington year, sow sweet corn between Apr 21 to Jul 21, keyed to the state's median last frost around Apr 14. 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 sweet corn 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.