Unlike true potatoes, which are started from whole or sliced tubers, the sweet potato is propagated from the shoots that erupt from the seed tuber once it is coaxed into growth in the spring. The gardener must plant the rootless “slip” right away in the prepared garden bed: Make a hole, stick the shoot in about halfway and space them 18 to 24 inches apart. You must keep the soil wet for a week or two until the slips grow roots. Instead of tugging them from the tuber, Harris cuts the shoots at soil level, which reduces the risk of a slip carrying a disease in the tuber.
A bed dedicated to sweet potatoes should be sunny, free-draining and sandy, which is why you need to amend the soil. Heavy clay soil just won’t do. Don’t add lime or high nitrogen fertilizers, but feed them with potash. The vines should be watered regularly; uneven moisture causes the potatoes to crack. The vines grow to three feet or more and need some space, along with good soil preparation. Joe Brunetti, a Smithsonian horticulturist who grows them at the Victory Garden at the American History Museum spaces them two feet apart. “I use a very loose loam. They do okay, a little knobbly,” he said. “If I were growing them to perfection I would absolutely add a lot more sand.” This, in turn, means watering them diligently to get them established and during dry spells.
Rodents can be a problem, particularly voles, and if you have rats in your urban plot, this might not be the crop for you. Harris’s crop is not bothered by critters, probably because they can’t tunnel into soil that is so sandy. Home gardeners do have an advantage over Harris: They can use tubers that are small and with splits that wouldn’t sell in the grocery store but are just as tasty.
Harris’s rejects are sold cheaply to people who like to feed deer, animal lovers and hunters alike. The variety Nancy Hall, in particular, has grudging tubers. They are thin and fingerlike, and sometimes a vine will produce no tubers at all. But to Harris, this variety is the ultimate sweet potato in flavor and texture. “Half the reason we are growing Nancy Hall is so we have them to eat,” he said, holding a clump and adding that he “couldn’t go through life” without eating the variety.
He rescued three of the varieties from a grower who was retiring about a decade ago. He bought the farmer’s equipment, seed potatoes and two seasons of growing advice, but not before the old-timer came to Harris’s farm in Salem County to see whether he had the right conditions. Harris later acquired the warmer zone farmland in Cape May, about a 45-minute ride to the east.
Sweet potatoes will keep well into the spring if they are handled and stored properly. Cuts and bruises from digging or rough treatment will cause them to rot. Dig them carefully and never wash them until you are ready to cook with them. And they must be cured by lying out in a warm room for a week or more. Harris keeps them at 80 degrees for two weeks before storing them in a cool room. Temperatures must stay above 55 degrees to prevent spoiling — they are not for the traditional cool root cellar.
Curing not only preserves them, it improves the flavor in some varieties. “I won’t sell Puerto Rican or Nancy Hall unless they have cured,” Harris said. “Their flavor doesn't really peak until Christmastime.”
Growing in 2013
Sources of slips for late spring planting:
Marlboro Farm Market
, Bridgeton, N.J. Five heirloom varieties of yams and Jersey sweets. No shipping and limited availability. Call in the spring for details: 856-451-3138.
Sand Hill Preservation Center
, Calamus, Iowa. Large selection of sweet potato varieties. The 2013 sweet potato catalogue is available next month. 563-246-2299
Southern Exposure Seed Exchange
, Mineral, Va. Good selection of varieties. 540-894-9480.
You can also start slips from organically grown tubers from the grocery store. In early to mid-April, set the tuber, vine end up, in a glass of water and grow in a bright location indoors. Harvest the slips for planting outside around Memorial Day.
Mouthwatering sweet potato recipes
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