When to plant sweet corn in Washington
Washington’s average last spring frost is April 20, and the first fall frost typically arrives around October 15 — about 178 frost-free days (USDA zones 4b, 5b, 6b, 7b, 8a, 8b, 9a). Sweet Corn needs 60–100 days to mature, which fits comfortably within Washington's growing season.
Washington covers a wide range of climates, so your exact frost dates may differ from the state average by two weeks or more. For dates tuned to your town, use the calendar generator.
When to plant sweet corn in Washington: the short answer
For a spring planting, sow Apr 22 – May 11. Wait until the soil is at least 55°F and frost is over.
Succession sow again in Washington: May 11 · May 25 · Jun 8 · Jun 22 · Jul 6 · Jul 20
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow sweet corn in Washington, step by step
- Prepare the bed. It needs at least six to eight hours of direct sun a day and loose soil at least 24 inches deep, with a pH between 5.8 and 7.0. Dig in compost before planting.
- Sow outdoors (Apr 22 – May 11). Space plants about 10 inches apart in rows 30 inches apart, sowing seed 1.5 inches deep. It is killed by frost, so nothing goes outside until the danger has passed.
- Water and feed. It needs plenty of water; keep the soil evenly moist and never let it dry out.
- Watch for pests and problems. Pests: corn earworm, European corn borer, corn rootworm, raccoons. Diseases and disorders: common smut, common rust, Stewart's wilt.
- Harvest (from about Jun 26 – Aug 5). Sweet Corn takes 60-100 days to reach harvest. Plant in a block of at least 4 short rows, not one long row, or the ears fill unevenly. Keep sugar-enhanced and supersweet types isolated from field corn. Succeed by sowing every 2 weeks or planting early/mid/late varieties together.
Figures come from our crop data; dates use Washington’s average frost dates. More in the full sweet corn growing guide.
Sweet Corn planting dates by USDA zone in Washington
Washington spans USDA zones 4b, 5b, 6b, 7b, 8a, 8b, 9a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the sweet corn dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant sweet corn |
|---|---|---|---|---|---|
| Zone 4 | May 10 | Sep 25 | 135 days | - | May 12 – May 31 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | - | May 2 – May 21 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | - | Apr 17 – May 6 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | - | Apr 7 – Apr 26 |
| Zone 8 | Mar 20 | Nov 5 | 230 days | - | Mar 22 – Apr 10 |
| Zone 9 | Feb 20 | Nov 30 | 280 days | - | Feb 22 – Mar 13 |
When to plant sweet corn in nearby states
| State | Last frost | Sow |
|---|---|---|
| Washington (this page) | April 20 | Apr 22 – May 11 |
| Oregon | April 20 | Apr 22 – May 11 |
Questions gardeners in Washington ask
When is the best time to plant sweet corn in Washington?
Sow sweet corn in Washington between April 22 and May 11. That timing is set by Washington's average last spring frost of April 20; Washington spans several climates, so cooler and higher parts of the state run later.
What is the latest I can plant sweet corn in Washington?
About August 16. Sweet corn needs at least 60 days to mature, and frost around October 15 ends the season, so later plantings risk being cut short.
When will sweet corn planted in Washington be ready to harvest?
Planted on time, sweet corn is usually ready from about June 26 to August 5, 60-100 days after sowing.
When is the last frost in Washington?
On average around April 20, with the first fall frost around October 15 - about 178 frost-free days. Your town may differ by two weeks or more.