Washington · zones 6b–9a
When to plant watermelon in Washington.
Sow between May 5 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
Watermelon dates for a typical Washington season.
Direct sow
May 5 to Jun 21
Keyed to the ~Apr 14 last frost. Sow 1" deep, 36" apart.
Harvest
~85 days later
~20 lb per plant over ~3 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.
In Washington: watch for
The pests that find watermelon here.
A middle-length season, about 187 frost-free days, means watermelon overlaps cucumber beetles for a stretch each summer. Check plants every week or two and treat early.
Striped or spotted beetles chewing leaves, blossoms and rinds.
Organic fix: Row cover until the first female flowers open, then hand-pick in the morning.
Clusters on the growing tips; sticky film on the leaves below.
Organic fix: Hose them off, or use insecticidal soap.
Anthracnose & gummy stem blight
Dark sunken spots on leaves and fruit after a humid stretch.
Organic fix: Rotate away from cucurbits, keep foliage dry, remove infected vines.
Your season math: Washington gives watermelon about 187 frost-free days, and it needs roughly 85 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting watermelon in Washington: questions
When should I plant watermelon in Washington?+
In a typical Washington year, sow watermelon between May 5 to Jun 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 watermelon 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.