Root Vegetable

When to Plant Sweet Potatoes in Washington

Not related to regular potatoes at all. Sweet potatoes need heat and a long growing season but reward with incredible harvests.

The Short Answer

Sweet potatoes in Washington State are an eastern-Washington-only proposition — and even there, it's a stretch. The hot Yakima Valley and Columbia Basin provide the best chance, with black plastic mulch and 90-day varieties. Western Washington's cool maritime climate cannot support sweet potato production.

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

Sweet Potatoes 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
8 wks before frost
Transplant Outside
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
8 wks before frost
Transplant Outside
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
8 wks before frost
Transplant Outside
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
8 wks before frost
Transplant Outside
3 wks after frost

Growing Sweet Potatoes in Washington

State-Specific Growing Tips

Eastern Washington: plant slips in late May to early June. Black plastic mulch is essential. Choose 90-day varieties. The hot Columbia Basin summers provide adequate heat, but cool nights can slow growth. Harvest before first frost (typically early October in eastern WA). Western Washington: do not attempt. The cool, cloudy Puget Sound climate cannot provide the sustained heat sweet potatoes require.

Recommended Varieties for Washington

Beauregard (90 days) is the only realistic choice for eastern Washington. WSU Extension does not specifically recommend sweet potatoes for most of the state.

Common Challenges in Washington

Season length is the fundamental constraint even in eastern WA. Cool nights below 55°F slow growth. Western WA is unsuitable. The crop is experimental in Washington — manage expectations.

Growing Tips

Grow from slips, not seeds. Start slips from a sweet potato in water 8 weeks before transplanting. Cure harvested tubers in warmth for 10 days.

Companion Planting

Plant sweet potatoes alongside these companions for better growth:

Beans Corn

Keep sweet potatoes away from:

Squash

The Bottom Line

Sweet Potatoes 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

Sweet Potatoes Growing Guide National planting guide with all states Washington Planting Calendar All plants for Washington Sweet Potatoes in Alabama Alabama planting dates Sweet Potatoes in Alaska Alaska planting dates Sweet Potatoes in Arizona Arizona planting dates Sweet Potatoes 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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