Warm-Season Vegetable

When to Plant Watermelon in Washington

The ultimate summer treat. Watermelons need heat, space, and patience — but the payoff is pure joy.

The Short Answer

Eastern Washington grows outstanding watermelons — the Hermiston area is famous regionally for its sweet, sun-ripened melons, and the Yakima Valley's hot summers create ideal growing conditions. Western Washington is essentially unsuitable for watermelons: the cool, cloudy Puget Sound climate cannot provide the sustained heat that melons absolutely require.

Washington Frost Dates

Your planting dates depend on which part of Washington you're in. Here are the frost date ranges by region:

Region Zones Last Frost (Spring) First Frost (Fall)
Western Washington (Seattle/Tacoma) 8a, 8b Mar 25 - Apr 15 Oct 25 - Nov 15
Puget Sound 8b, 9a Mar 15 - Apr 5 Nov 1 - Nov 20
Eastern Washington 5b, 6a, 6b, 7a Apr 25 - May 15 Sep 25 - Oct 15
Central Washington 6a, 6b, 7a Apr 20 - May 10 Oct 1 - Oct 20

Watermelon Planting Schedule for Washington

Western Washington (Seattle/Tacoma) (Zones 8a, 8b)

Average last frost: Mar 25 - Apr 15 · Average first frost: Oct 25 - Nov 15

Start Seeds Indoors
3 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
3 wks after frost

Puget Sound (Zones 8b, 9a)

Average last frost: Mar 15 - Apr 5 · Average first frost: Nov 1 - Nov 20

Start Seeds Indoors
3 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
3 wks after frost

Eastern Washington (Zones 5b, 6a, 6b, 7a)

Average last frost: Apr 25 - May 15 · Average first frost: Sep 25 - Oct 15

Start Seeds Indoors
3 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
3 wks after frost

Central Washington (Zones 6a, 6b, 7a)

Average last frost: Apr 20 - May 10 · Average first frost: Oct 1 - Oct 20

Start Seeds Indoors
3 wks before frost
Transplant Outside
2 wks after frost
Direct Sow
3 wks after frost

Growing Watermelon in Washington

State-Specific Growing Tips

Eastern Washington: transplant from mid-May when soil reaches 70°F. Black plastic mulch accelerates soil warming. The hot days (90°F+), cool nights, and intense sun of the Columbia Basin produce exceptionally sweet melons. Drip irrigation is essential in the arid climate. The volcanic soils of eastern Washington are well-drained and productive with irrigation. Western Washington: not recommended. Even in unusually warm years, Puget Sound gardens rarely accumulate enough heat units for melon maturity. If you must try, grow Sugar Baby against a south-facing wall with black plastic mulch and row cover.

Recommended Varieties for Washington

Eastern Washington: Crimson Sweet, Jubilee, Sugar Baby, and Orangeglo all perform well. Hermiston Sweet is a regional variety with a devoted following. Western Washington: if attempting, Sugar Baby (75 days) is the only realistic option. WSU Extension's irrigated agriculture research provides melon variety trial data for eastern Washington.

Common Challenges in Washington

Eastern Washington: minimal disease thanks to dry climate. Spider mites in hot, dry conditions. Inconsistent irrigation causes cracking. Western Washington: insufficient heat is the fundamental and often insurmountable challenge.

Growing Tips

Black plastic mulch warms soil faster. Check ripeness by looking for a yellow ground spot and listening for a hollow thump.

Companion Planting

Plant watermelon alongside these companions for better growth:

Corn Sunflowers Marigolds

Keep watermelon away from:

Potatoes

The Bottom Line

Watermelon can be grown successfully in Washington with proper attention to regional frost dates and local growing conditions. Timing varies across the state — Western Washington (Seattle/Tacoma) gardeners work with a last frost around Mar 25 - Apr 15, while Central Washington sees frost end around Apr 20 - May 10. Choose varieties suited to your region, amend your soil based on its specific needs, and monitor for the pests and diseases most common in your area. For exact dates based on your zip code, use our free planting date finder.

Related Guides

Watermelon Growing Guide National planting guide with all states Washington Planting Calendar All plants for Washington Watermelon in Alabama Alabama planting dates Watermelon in Alaska Alaska planting dates Watermelon in Arizona Arizona planting dates Watermelon in Arkansas Arkansas planting dates
Note: All dates are based on NOAA 30-year Climate Normals and represent historical averages, not predictions for any specific year. Always check your local weather forecast before planting frost-sensitive crops. Learn about our data sources.

Last reviewed: March 29, 2026

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