Ornamental sweet potato vines come in many varieties and colors, and look beautiful as ground covers or for contrasts in pots and hanging baskets. Many people toss these plants at the end of summer and replace them each spring (at a cost of $3-$5 per pot) but there is an easy method to overwinter them, even in harsh climates.
After the first frost, the leaves on the vines will die, making it easier to handle the plant. Cut away the dead portion of the leaves and vines, leaving just a couple of inches of old growth showing.
With your hands or a small garden shovel, loosen the soil around the base of the vine. Keep digging downward, following the roots on the vine, until you feel the potatoes. Continue to collect these potatoes as you dig downward. I prefer using my hands so that I don't break portions of the potatoes.
Some plants, such as Ipomoea batatas 'Margarita' will usually have large, roundish potatoes, while others, such as Ipomoea batatas 'Blackie' will have smaller, slender potatoes. Also of note is that the lime green ornamentals tend to have potatoes with a reddish skin while the darker purple vines will sometimes have a lighter color skin (I've found that newer varieties can have either). I use my tags that were buried within the pot to re-tag the potatoes after digging.
After collecting and tagging your potatoes, allow the potatoes to air dry overnight. Next, it's time to box them up. Choose a box that will easily hold all of the potatoes you intend to keep. Layer the bottom of the box with newspaper, then tear strips of newspaper to form a cushion in the bottom of the box. Place a layer of potatoes, then cover with newspaper strips, then a section of newspaper. Continue to add layers of newspaper and potatoes until your box is full or until you run out of potatoes.
Store your box of potatoes in a cool, dry place over winter. I store mine in the garage; in colder climates you will need to store them where the temperature will be above freezing.
In spring, after danger of frost, replant your potatoes wherever you'd like to have your ornamental vine growing. If your potatoes have already grown eyes and have begun to sprout, you can cut them into sections and plant just as you would a regular potato. Enjoy through summer, then begin the harvest again for next season--no need to buy new plants every spring!
Here are some of my plants in October, just before our first frost.