When to plant watermelons 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). Watermelon needs 70–100 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 watermelons in Washington: the short answer
For a spring planting, plant out Apr 27 – May 14, with seeds started indoors Mar 23 – Apr 6. Wait until the soil is at least 70°F and frost is over.
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 watermelons in Washington, step by step
- Start seeds indoors (Mar 23 – Apr 6). Sow seeds 1 inch deep in seed-starting mix under bright light. They take 4-10 days to sprout, fastest in soil around 85°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 24 inches deep, with a pH between 5.5 and 6.8. Dig in compost before planting.
- Plant out (Apr 27 – May 14). Space plants about 36 inches apart in rows 72 inches apart. It is killed by frost, so nothing goes outside until the danger has passed.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: striped cucumber beetle, aphids, squash vine borer. Diseases and disorders: anthracnose, fusarium wilt, powdery mildew, gummy stem blight.
- Harvest (from about Jul 13 – Aug 12). Watermelon takes 70-100 days to reach harvest. Longest-season cucurbit here - icebox varieties (70-75 days) are the realistic choice north of the mid-Atlantic. Ripe when the curly tendril nearest the fruit is brown and dry and the ground spot is buttery yellow.
Figures come from our crop data; dates use Washington’s average frost dates. More in the full watermelon growing guide.
Watermelon 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 watermelon dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant watermelon |
|---|---|---|---|---|---|
| Zone 4 | May 10 | Sep 25 | 135 days | Apr 12 – Apr 26 | May 17 – Jun 3 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Apr 2 – Apr 16 | May 7 – May 24 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Mar 18 – Apr 1 | Apr 22 – May 9 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Mar 8 – Mar 22 | Apr 12 – Apr 29 |
| Zone 8 | Mar 20 | Nov 5 | 230 days | Feb 20 – Mar 6 | Mar 27 – Apr 13 |
| Zone 9 | Feb 20 | Nov 30 | 280 days | Jan 23 – Feb 6 | Feb 27 – Mar 16 |
When to plant watermelons in nearby states
| State | Last frost | Plant out |
|---|---|---|
| Washington (this page) | April 20 | Apr 27 – May 14 |
| Oregon | April 20 | Apr 27 – May 14 |
Questions gardeners in Washington ask
When is the best time to plant watermelons in Washington?
Plant watermelon transplants outdoors in Washington between April 27 and May 14. 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.
When should I start watermelon seeds indoors in Washington?
Start seeds indoors between March 23 and April 6, about 3 weeks before the last frost, so the seedlings are ready to plant out from April 27.
What is the latest I can plant watermelons in Washington?
About August 6. Watermelons need at least 70 days to mature, and frost around October 15 ends the season, so later plantings risk being cut short.
When will watermelons planted in Washington be ready to harvest?
Planted on time, watermelons are usually ready from about July 13 to August 12, 70-100 days after planting.
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.