Warm-Season Vegetable

When to Plant Squash (Summer) in Washington

Zucchini and yellow squash are the garden's most generous producers. You'll be sharing with neighbors by midsummer.

The Short Answer

Washington State's squash growing is yet another story of the east-west climate divide. Western Washington's cool, cloudy summers are surprisingly good for summer squash — zucchini and yellow squash produce reliably even in the Puget Sound region's moderate heat. Eastern Washington's hot, sunny, irrigated conditions grow winter squash and pumpkins that rival any in the country. The key difference from eastern states: significantly lower pest and disease pressure thanks to the dry climate.

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

Squash (Summer) 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
2 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
2 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
2 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
2 wks after frost

Growing Squash (Summer) in Washington

State-Specific Growing Tips

Western Washington: direct sow from late May to early June when soil reaches 60°F. Summer squash grows well in the Puget Sound region — unlike tomatoes and peppers, squash doesn't need intense heat to produce. Start winter squash indoors in early May for transplanting in early June to ensure maturity before fall. Eastern Washington: direct sow from mid-May and enjoy hot, productive conditions. WSU Extension's irrigated agriculture research near Prosser provides excellent variety trial data. In western Washington's acidic clay soils, add lime if pH is below 6.0 and amend with compost for drainage.

Recommended Varieties for Washington

Western Washington: Black Beauty and Costata Romanesco for summer squash. For winter squash, choose shorter-season varieties: Delicata (100 days), Butternut Waltham (110 days), Sweet Dumpling (100 days). Eastern Washington: grow any variety including long-season types. Blue Hubbard, Red Kuri, and Kabocha are popular with eastern Washington farmers market growers.

Common Challenges in Washington

Western Washington's main squash challenge is slugs — they're voracious on young seedlings. Use iron phosphate bait (safe for pets and wildlife) or handpick at dusk. Powdery mildew appears later in the season but is less aggressive than in the humid East. Eastern Washington has very few squash pest or disease issues thanks to the dry climate, but spider mites can build up on stressed plants. In both regions, squash vine borer is rare — it's one of the genuine advantages of Pacific Northwest growing.

Growing Tips

Harvest when fruits are 6-8 inches long for best flavor. Larger squash become seedy and tough.

Companion Planting

Plant squash (summer) alongside these companions for better growth:

Corn Beans Nasturtiums

Keep squash (summer) away from:

Potatoes

The Bottom Line

Squash (Summer) 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

Squash (Summer) Growing Guide National planting guide with all states Washington Planting Calendar All plants for Washington Squash (Summer) in Alabama Alabama planting dates Squash (Summer) in Alaska Alaska planting dates Squash (Summer) in Arizona Arizona planting dates Squash (Summer) 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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