VANCOUVER, Wash. — Sweet potatoes could have a future as a staple crop in northern latitudes.

“We can grow them here. They’re great for climate resilience,” said Laura Schulz, a Washington State University doctoral student.

She added there’s excitement for locally grown sweet potatoes, and farmers see brisk sales.

Schulz gave a presentation on the vegetable Nov. 15 during the Tilth Conference, an annual organic expo.

WSU has been conducting sweet potato research for six years and has on-farm trials with 32 growers in Western Washington. Yields have been comparable to the national average.

“I think Eastern Washington is a great place for sweet potatoes, too,” Schulz said.

Long days promote growth

Sweet potatoes, which are a heat- and sun-loving crop, require 90-120 frost-free days and have low nutrition requirements.

North Carolina leads the nation in production, and California is the top state for organic sweet potatoes.

Long days in the Pacific Northwest’s early summer promote vine growth and short days in fall help root bulking.

Low temperatures limit development, so plastic mulch or other coverings are critical to warm the soil.

Growers should try to avoid heavy clay soils and can produce different size roots through the timing of harvest and plant spacing. Schulz said fingerling sweet potatoes have been a hit for some farmers.

Orange sweet potatoes tend to have higher yields than white- or purple-fleshed varieties.

Top NW varieties

Cascade, a new USDA sweet potato, has been performing quite well in Western Washington trials. The white-fleshed variety is resistant to wireworm, the most significant pest for the vegetable in the Northwest.

Bayou Belle is another strong variety for the Northwest because it’s somewhat resistant to wireworm and yields are quite high.

To minimize wireworm, growers should avoid fields with recent grasses or clover, and annual tillage reduces populations.

Other benefits of Cascade are that it’s early maturing and produces slips quickly, with many slips per root. Cascade also was the top crop in taste tests of local consumers, said WSU plant breeder Carol Miles.

Schulz recommended that growers produce their own slips, as there have been problems with disease from commercial suppliers.

Raised beds make harvest easier, and wilting and dieback after planting is normal.

“There’s a lot of transplant shock happening. They have no roots. … We always recommend giving them a few weeks,” Schulz said.

Long storage, leafy byproduct

Sweet potatoes should be harvested before soil temperatures drop below 50 degrees.

Washing isn’t recommended afterward, as that can strip skin away.

Curing requires high temperatures and high humidity, but sweet potatoes can be stored for as long as a year.

Some farmers cure their sweet potatoes with winter squash for efficiency.

Sweet potato leaves are edible and sold at many Asian markets. They should be clipped right before harvest. Vines also can be used as livestock feed.

Farmer perspective

Kia Armstrong, owner of Beanstalk Farm near Sequim, Wash., is a trial grower and said she’s interested in sweet potatoes because climate change is making the Olympic Peninsula warmer.

She said the crop could make sense for farms with direct sales, and growers can experiment to see if sweet potatoes fit into their longterm planning.

“I wouldn’t recommend anybody go big on them right away,” Armstrong said.