With our first frost imminent here in Missouri, now is the time to harvest those sweet potatoes!
Most varieties of sweet potatoes are ready to harvest between 90 and 120 days of planting. The leaves begin to yellow, indicating that growth is slowing down. You can wait until the first frost to harvest sweet potatoes, in fact, some folks claim that they are better if you do, but you must be ready to get them out of the ground immediately. Depending on the size and number of your beds, this may not be feasible. However, you will still be rewarded with sweet pickings if you harvest shortly before the first frost.
As you dig up your sweet potatoes, be gentle with your harvesting equipment. Carefully loosen the soil with a digging fork and gently pull them from the ground by their crowns. Excessive injuries to the skin and flesh can cause infection and disease that will ruin your sweet gems before you can enjoy them. Do not wash the tuberous roots after harvest; a gentle brushing will remove any loose soil that clings to their skin.
Once dug, sweet potatoes need to be cured to bring out their sweetness, to improve their nutritional value, and to ensure that they will store longer over the winter. During the curing process, starches are changed to sugars and a second skin forms for their protection. To properly cure your sweet potatoes, arrange them in a single layer in boxes and keep them in a warm, humid location around 80-85 degrees F and 85-90 percent relative humidity for 6 to 10 days. Proper ventilation is necessary to prevent the accumulation of carbon dioxide and condensation. For the home grower, these conditions can be created and maintained in a warm bathroom by covering them with wet towels or setting jugs of hot water around them. After curing, sweet potatoes are best stored at between 55 and 60 degrees F and at 95 percent relative humidity to keep them from sprouting.
Although it may seem like a lot of work, meticulous preparation will pay off. Properly cured sweet potatoes can last up to 10 months under ideal storage conditions!
If you would like to learn more about growing and harvesting sweet potatoes here in Missouri, the University of Missouri Extension has provided us with an excellent publication that can be downloaded for free: Growing Sweet Potatoes in Missouri
Best wishes and happy eating!