Sweet potatoes are one of the most nutritionally complete foods grown. A natural choice for meals during the holiday season, they are one of the few vegetables that serve dual purpose as either a vegetable dish or a dessert. Sweet potatoes develop their swollen, fleshy roots toward summer's end and into the fall. Roots can be harvested anytime after they begin to size, but they can also be left in the soil until the first light frost to maximize yield. Since they are a tropical plant, the first frost will kill most of the leaves. Although frost will not harm the roots, they should be dug promptly before cold temperatures and cold, wet soils affect them.
Tony Bratsch, University of Illinois Extension horticulture educator, offers the following advice for harvesting and storing sweet potatoes. Roots bruise easily, so care should be taken during digging. After harvest, carefully rub off any soil that clings to the roots and let them dry on the soil surface for a few hours in the sun. Do not leave the potatoes outdoors overnight. Any sweet potatoes that are cut or bruised during digging should be separated from the others and eaten first. They will exude a milky juice if damaged, but this does not seal the wound or protect against rot-producing bacteria and fungi.
For best storage, sweet potatoes should be cured after the brief sun drying. Curing helps heal light surface wounds and toughens the skin. Curing is done by placing the sweet potatoes in a steady temperature of 80 to 85 degrees, for a week to ten days. A small, heated outdoor shed or furnace room can serve this purpose. A loose covering of plastic can help maintain humidity during that period. If kept too warm at low humidity, the roots will begin to shrivel and lose quality.
After curing, the sweet potatoes can be stored for the winter in crates or baskets. Store them in a location where temperatures stay 55 to 60 degrees, with high humidity of 80 to 85 percent to keep roots from shriveling. Many basements approximate these conditions, but maintaining high humidity can be a challenge. Draping plastic bags or plastic sheets with holes in them can help hold up the humidity and increase storage time. Make sure any plastic wrapped around the potatoes has enough holes to provide good air exchange and not allow excessive moisture build-up. Do not store sweet potatoes in outdoor pits, root cellars or locations where temperatures drop below 50 degrees. These conditions will reduce storage life and promote decay.
A common problem we see when sweet potatoes are dug is scurf, a disease caused by a soil fungus. If you have irregularly colored, dark brown or nearly black potatoes, scurf may be the culprit. Scurf does not make the potatoes inedible, but it greatly reduces storage life. Once the disease has been introduced into the garden, there is no chemical control, and it will remain a problem for many years. Only by rotating into a new area can this disease be avoided. If you do not have room for a new site, then rotate each year to a new spot in the current garden to help reduce build-up after it has been introduced.
Never use transplants grown from sweet potatoes containing scurf. If it is a problem, purchase only certified, disease-free plants. Also, be careful accepting new planting slips from well-meaning neighbors. To help prevent the spread of scurf, thoroughly clean tools and equipment used in infected soil. For more information about growing sweet potatoes and other vegetables, check out the "Vegetable Gardening in the Midwest" book available from your local U of I Extension office. Or, log on to Extension's "Illinois Vegetable Garden Guide" website at http://web.extension.uiuc.edu/coles/. Click on Horticulture & Environment. Look under additional websites. Till next time, this is Becky Litterer from Becky's Greenhouse, Dougherty Iowa