Growing a new market
While there isn’t any area poised to surpass North Carolina in the production of sweet potatoes, trials are showing promise of the crop in colder climates.
Members of the morning glory family, most of the U.S. sweet potato crop is grown in California, Louisiana and Mississippi, with close to 40 percent originating in North Carolina.
Highly nutritious and packed with beta-carotene, sweet potatoes are earning popularity in baked, fried and other value-added forms, such as diced sweet potatoes, purees, flakes, flour and fresh cuts.
Adapting to cold climates
Native to South America, the sweet potato prefers a sandy soil and a long growing season, but can be adapted to other conditions. Jim Ballerstein, research support specialist at the New York State Agricultural Experiment Station in Geneva, says although some home gardeners grow the vegetable, it’s generally been dismissed as a southern crop.
Ballerstein and some growers in the Lake Ontario region who enjoy a microclimate that is one growing zone warmer than the surrounding area are giving sweet potatoes a try. To compensate for their differences from traditional growing areas, plastic mulch with drip irrigation is employed. Planting in beds is helpful in gaining soil warmth in the spring and fall. The expense and labor involved with mulch and irrigation do make an otherwise low-input crop more costly than in traditional growing areas.
New Yorkers have found that fencing is also essential, as deer and woodchucks are big sweet potato fans. Mice can also slip through the plastic and render the tubers unmarketable. One grower found that keeping the soil moist discourages the rodents and is preferred by the plants, although they will tolerate dry conditions. Few insect problems have been noted.
The most critical practice in colder climates is to harvest the roots prior to the soil temperature dipping below 50 degrees. Exposure to cold reduces the storage life. Ballerstein recommends a late September harvest. With good curing and storage processes, sweet potatoes remain edible for up to one year.
Testing the crop
New sweet potato growers should analyze the market and may find that some consumer education may be needed to create demand. Conversely, trends toward healthier, local food choices may indicate a desire for new and diverse produce. A small, trial plot of about .25-acre (1,500 plants) will yield 1,500 to 2,000 pounds. Typical plants yield 2 to 3 pounds each with at least 50 percent of that of marketable quality.
Ballerstein’s production guide begins with ordering quality plants. He recommends Scott Farms in North Carolina (www.scottfarms.com, 877-284-4030). Additional sources can be found online at www.ncsweetpotatoes.com. Keep them cool, but not refrigerated. After preparing and fertilizing the ground, form beds and lay plastic and irrigation tape.
Soak the plants in water the night before planting. Punch holes in the plastic and set the plants 15 inches apart, 3 to 4 inches deep, with starter fertilizer. Ballerstein recommends feeding nitrogen through the drip tape when the plants are established. An herbicide may be used between rows, with hand-weeding required for any invasions arising through the openings in the plastic.
Between planting and harvesting, the plants require little tending. Shortly before harvest time, the plants can be pulled back to facilitate the process. Bushhogging the plants may be considered. Remove the plastic by splitting down the middle through the plant openings and pulling away from the beds. Hand-harvesting has been practiced in the small experimental plots, but mechanized equipment is available.
Sweet potatoes are graded as smalls or culls at thumb size, marketable in a range of small and large sizes and jumbo if over 2 pounds. Cure the crop by brushing away dirt, but not washing. Place in a greenhouse or other location that is heated to about 80 degrees and has high humidity for four to five days. This process allows the potatoes to heal over any cuts or scrapes. Properly cured, they will store well in a cool (50 to 60 degrees) location. Sweet potatoes should not be refrigerated.
Gary Samascott has grown the crop for three years in Kinderhook, N.Y. Samascott and his brother Ron are primarily apple growers, but have expanded to a wide range of other fruits and vegetables. They sell their produce at the farm market and at a Rockefeller Center market in New York City.
Like Ballerstein, Samascott has started small, growing .5 acre on black plastic with irrigation. He finds production is enhanced during warmer summers, although he agrees that the raised beds add some warmth. Samascott also battles deer.
“We’re learning [the crop] and may grow more next year,” he says, adding that sweet potatoes sell very well in the Big Apple.
Ballerstein recommends that those who are interested in trying this crop start small and consider their market. Winter squash customers may be good candidates for sweet potatoes. Their long storage life is a bonus for these nutritious and tasty vegetables. Offer recipes and samples and encourage local restaurants to give fresh, local sweet potatoes a try. Many cultivars with varying flesh consistency and color and skin hue exist and distinct populations tend to like different types. For instance, many people of Asian heritage prefer the drier, white-fleshed varieties, such as Japanese.
Ballerstein continues to study cold climate sweet potato production. He is evaluating various short season cultivars to pinpoint the optimal types for his region. He’s eliminated Vardamann, Centennial and Georgia Jet, as they were less uniform and smaller in his trials. Carolina Ruby has offered the best yield, with the Beauregard cultivar producing the most uniform crop. Carolina Ruby, Covington, Hernandez and O’Henry are Ballerstein’s top picks.
He’s experimenting with the best plant spacing, as well, but hasn’t seen great differences between using 12, 15 and 18-inch distances. In 2009, he tested infrared transmitting [IRT] plastic and noted a .5-pound yield increase per plant as opposed to black plastic; that study will be replicated this year. He plans to investigate the use of plugs, rather than slips, when research dollars become available.
“I have worked with these on a small basis for years, but with no real funding,” Ballerstein adds. “If our funding proposal is approved, we can devote more time to this interesting crop.”
Based in Greensboro, N.C., the author writes articles about horticulture, landscaping, agriculture and travel. She has been a contributor to Moose River Media publications for three years.