Sweet potatoes are a common vegetable crop but aren’t typically thought of in the cover crop lineup. But this low-lying, drought-resistant crop is recommended by the Food & Agriculture Organization of the United Nations (FAO) as a cover crop.
Be careful not to confuse sweet potatoes with yams — they are two entirely different crops.
This soil-preserving crop is also very prolific at harvest time, yielding between 29,000-32,000 lbs./acre. Based on those figures, that means sweet potatoes are returning between 3,940-4,260 pounds of carbon and 198-215 pounds of nitrogen (N) per acre.
An herbaceous, perennial trailing vine, sweet potatoes must be planted from mid-May to late June — well after the threat of frost has subsided, according to information from Alcorn State University Extension in Mississippi. Cold, wet soil can cause sweet potato slips to rot, so make sure that the soil has warmed up and is dry before planting.
You can also plant sweet potato cuts, like you would potatoes, but the cuts may end up becoming dinner for wildlife like squirrels or raccoons.
The Beauregard variety of sweet potatoes is one of the most common, as it is very productive and easy to grow. There are several other varieties that can also be considered as well, including Georgia Jets, Bill Shane’s white, Jubilee, Bush Porto Rico, Centennial, Jewell, Sumor and Vardaman.
The warm-season crop grows best in soils that are sandy loam or sandy with a pH between 5.8-6.2. You may want to do a soil test before planting sweet potatoes, because too much potassium (K) in the soil can make tubers taste bitter. Sweet potatoes can also be used in place of any brassica as part of a cover crop mix.
Because sweet potatoes are allelopathic, they can be rotated with other cover crops to help prevent insect and soil-borne disease issues, according to an article from the American Society of Agronomy. Sweet potato weevils, black-rot, stem-rot, root-knot nematodes, flea beetles, wireworms and cutworms are all possible pests to watch out for when growing sweet potatoes.
Scurf fungus, black rot fungus, ring rot, circular spot, fusarium, soil rot, streptomyces root rot bacteria, and feathery mottle virus are additional diseases that can hurt production. Rodents and wildlife such as deer, rabbits, groundhogs, pocket gophers, voles, rats and field mice can also be a problem, according to information from University of Wisconsin Extension.
The first month after planting is the root development stage, with roots going as deep as eight inches in 40 days. The second month, the plants focus on vine growth, while the roots store starch and sugar close to the base of the stem. During the last month is when the actual tubers develop.
About 2 weeks prior to harvest, stop any additional watering. This allows the sweet potato skin to harden, making it more durable and less prone to rot.
Harvesting can occur any time after mid-September, or 90-120 days after planting, or before soil temperatures reach 55 F. If frost does sneak up on you, harvest sweet potatoes within a few days, although if days are warm, a couple of light frosts will not harm sweet potatoes. Sweet potatoes can also be left as green manure in the field, if you prefer not to sell them as a cash crop.
Tubers should be allowed to dry for an hour before storing, although temperatures above 90 F can cause sun scald if tubers are exposed for more than 30 minutes. With such a high yield, sweet potatoes are an excellent choice for growers looking to make money off a cover crop.
Have you ever grown sweet potatoes as a cover crop? We’d love to hear about your experience!