This article was written by Mary Roduner, former SDSU Extension Consumer Horticulture Field Specialist.
It seems like everywhere I’ve gone this summer someone has asked about sweet potatoes. Usually the question goes like this “This is my first year growing sweet potatoes. When do I dig them? What do I do with them?” For all you who are growing them for the first time or have had limited success after they are dug, this is for you.
Sweet potatoes are a vine in the morning glory family, Ipomea batatas, and not related to regular or “Irish” potatoes in the nightshade family. The long vines of sweet potatoes can overrun a garden. In early to mid-September, feel free to cut them back by 25%. This simply makes the plants easier to deal with when digging.
The two best varieties for South Dakota, Beauregard and Georgia Jet, have approximately 90 day growing seasons. Because our warm growing season is short, the plants need to stay in the ground as long as possible to allow the tubers to mature. Wait until the first light frost when the leaves have been nipped and have brown drying edges before you dig the tubers. Once there has been a hard frost and the tops are completely dead the tubers are at risk for rotting and need to be dug immediately. If your soil stays wet, reduce watering as the days get cooler and closer to frost. Wet soil is one of the main causes of tuber rot.
When digging the sweet potatoes, cut off the vines until you have found the base of each plant. Using a digging or potato fork, set the fork about 12” from the base of the plant. Dig straight down to prevent spearing and damaging the tubers. Gently lift the fork and shake off the dirt. Trim the “stem” on the tuber by snapping it off evenly. Do not wash the tubers because freshly dug and washed tubers will rot very quickly. Simply knock the largest dirt clumps off and leave the small stuff on them.
Sweet potato skin is very fragile when harvested and needs to be cured for long term storage. Find the warmest area of the house with moderate moisture, above 85° is best. Lay newspapers on the floor and spread the tubers out in a single layer with air space between them. Remove and use immediately any with fork or insect damage. Leave the tubers to dry for about 2 weeks. When the skins are dry and “tough” the potatoes can be put in boxes for storage. You can stack up the tubers but no more than three layers deep. Store the dried tubers in a location that will stay above 60°. If the temperature goes lower the tubers will become corky, stringy and inedible. Properly kept, sweet potatoes will stay firm for up to one year.
There have also been questions about eating the tubers under ornamental sweet potatoes. From personal experience they can be eaten but I would NOT recommend it. I baked one and there was no amount of salt, pepper, butter or gravy that could give it flavor and the amount of fiber was offensive, almost 200% of your daily requirement. Eating them won’t hurt you, but why bother!!??
After you’ve done the work to cure them, be sure to save one or two for next year’s slips. I will write about how to start your sweet potato plants for next year’s garden in the spring.