Margaret Lauterbach

This year, consider planting sweet potatoes

Sweet potatoes keep for months after harvest.
Sweet potatoes keep for months after harvest. TNS

While you’re planning your garden, think about planting sweet potatoes. They’re very nutritious and easily stored after harvest. In the past, many of us thought of sweet potatoes as southern products, but that’s primarily due to the preferred method of post-harvest curing the sweet potatoes. That curing depends on exposure to 85 degrees F. and 90 to 95 percent humidity for four to seven days. We will not have either those temperatures or that humidity when we dig our sweet potatoes, about October.

Unlike fruit and some other vegetables, sweet potatoes just keep growing until they’re dug. The longer they remain in the soil, however, the more they’re attacked by destructive soil-dwelling creatures and disease. Sweet potatoes need modest amounts of nitrogen and phosphorus to grow, but they need a fairly significant dose of potassium. My late friend Ross Hadfield, of Meridian, put a fertilizer tree spike in the irrigation line to his sweet potatoes one year, and harvested some giant tubers, four hills produced sweets that overflowed his wheelbarrow.

Garnette Edwards, of Edwards Greenhouse, said her grandfather did cure his sweet potatoes in his first house (abandoned when he built a new one for his growing family), heating the structure with a coal stove, probably with water containers on the stove to add humidity. He was known as the “sweet potato king” of Boise, and his crew sold them door-to-door after the curing.

Some folks say curing is mainly necessary to heal wounds incurred as they’re dug, so dig carefully and you won’t need to cure them. Curing also extends the storage life of the sweet potato, however. A period of a few days’ resting after harvest allows the starches to convert to sugars and other desirable flavor components. Sweet potatoes have very thin, fragile skins. Those skins will toughen up if you cut off vines about three to seven dry days before you intend to dig the sweet potatoes. If weather is wet and frost looms, cut vines just before digging.

One reference says that they will double their yield every two weeks, from the beginning to the end of September. They’re very vulnerable to frost, however, so if we have a predicted early frost, cover the vines. The botanic designation for sweet potatoes is Ipomoea batatas, and since the regular “Irish” potato is Solanum tuberosum, you can readily see they’re a different genus. They grow differently too.

In my experience, sweet potatoes grow vertically in a cluster (although there may be one or two stray), whereas regular potatoes grow like the fingernails on an outstretched hand. There is some linguistic indication, at least, that Polynesians obtained sweet potatoes from South America and dispersed them among the islands (including at least New Zealand, where they’re known as “kumaras”) before Columbus’s “discovery” and settlement of this continent. In Peru the Quechua name for a type of sweet potato is “kumar.” They are native to Central or South America, and have been found in 8,000-year-old graves. Traces have been found in Hawaii and Polynesia dating back to about 700 to 1000 AD. Since they don’t spread by seed, but by vine cuttings, they had to be transported by humans.

Those sweet potatoes for human culinary use may have orange, white, yellow or purple flesh. If you want to grow any of these variations, buy them at local grocery stores (ask first if they’ve been sprayed against sprouting), and put them in a warm place to sprout now. The sprouts are called “slips,” and they’re sold by some local garden stores as well as mail order sources. It’s less expensive to develop your own, and this is the time to do it. They can’t be transplanted out before all danger of frost is past. Instructive videos are on, such as .

Most sweet potatoes sold by grocery stores are either the orange-meated or the yellow-meated, and may be incorrectly called “yams.” The yellow-meated has a tan skin and is drier-meated than the orange-meated (redder skin), but delicious baked (oven or microwave) and cut across into fat coins for serving.

They grow as very attractive vines, so can be planted among other garden plants, the vines shading soil so that weed seeds won’t germinate. When squirrels demolished several of my broccoli, kale and Tronchuda plants last year, I filled in those spaces with sprouted sweet potatoes. Then squirrels began feeding on the slips and bits of sweet potatoes, so I had to use earth staples to affix wire baskets to the ground over the sweet potato starts. Squirrels could have eaten fallen apples or other fruit instead.

The leaves of sweet potato vines are edible, but perhaps not the black or chartreuse leaves of those Ipomoea vines that are sold for ornamental gardens. I’d caution against eating many of the leaves of the sweet potatoes you’re growing for tuber harvest, for they’re feeding those tubers.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83705.

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