If you’re like me, the start of the fall is not only fun because of the cooler weather it brings: it also ensures that I can put up my canning equipment. Beautiful, nutritious fall vegetables— winter squashes, onions and, of course, sweet potatoes — can be preserved for several months if well harvested and processed.
Sweet potatoes, with a strong vitamin content contained in their orange skin, are particularly large and durable fall and winter foods.
After watching the beautiful, winding vines cover your garden beds through the summer months, it can be hard to know when it’s the right time to go grab the spading fork and dig out the fleshy tubers. While sweet potatoes can be dug as soon as the tubers have reached a suitable size — between three and four months after planting the slips — the flavor and quality improves with colder weather.
Some even wait until after the first frost has blackened the leaves, but only if you can get all your sweet potatoes out of the ground quickly and right away. Rodale’s Encyclopedia of Organic Gardening makes the following recommendation: “You can harvest as soon as leaves start to yellow, but the longer a crop is left in the ground, the higher the yield and vitamin content. Once frost blackens the vines, however, tubers can quickly rot.”
The most common tool for digging sweet potatoes out of the ground is a spade fork, although a shovel will work, and the ambitious harvester can even adapt a broad fork to dig more plants at one time. If you have a large plot, you can adjust a mold-board plow to mechanically turn the sweet potatoes out of the ground. Tubers can grow a foot or more away from the plant, so give ample space to prevent nicking and damaging the skin, as this encourages spoilage. Digging is much easier when the soil is dry, and mud-coated sweet potatoes are less likely to sun-dry properly and rapidly.
Dry freshly dug sweet potatoes in the sun for a few hours, then move them to the healing room. Although you can cook fresh sweet potatoes out of the ground, natural sweetness improves after curing. Proper healing often restores injuries caused by tubers during planting, which helps to ensure effective preservation.
The simplest method for curing is to put sweet potatoes in paper-lined boxes in a dry, well-ventilated room — ideally between 85 and 90 degrees Fahrenheit at about 85 percent humidity — for a week to 10 days. A hoop house or green house works well for this, but any space where you can control the temperature will work. After curing, move the sweet potatoes to a storage space, such as a root cellar, kept between 55 and 60 degrees with humidity of 75 to 80 percent. (If you don’t have a root cellar, you can build your own basement root cellar.)