Although many people use the word yam and sweet potato interchangeably, they are really two separate plants. Orange sweet potatoes (Convolvulaceae) are sweet and moist, while true yams (Dioscoreaceae ) are dry and starchy. The United States Department of Agriculture allows sweet potato to carry the name of yam as long as it also contains the label sweet potato. Those labeled as yams in grocery stores across the US are almost certainly sweet potatoes. Although much of the US does not have a long enough growing season to produce mature sweet potatoes, they can be grown in water to create an interesting houseplant.
Select a firm sweet potato with no signs of damage. Examine it for soft spots, cuts or bruises, or areas of discoloration. To grow a healthy sweet potato vine, you need a healthy tuber.
Hold the sweet potato with the pointed end down. Insert three or four toothpicks at equal distance around the circumference of the potato, slightly above the midpoint.
Fill a jar with water and place the sweet potato, pointed end down, so the toothpicks rest on the rim of the jar, and the bottom half of the sweet potato rests in water.
Place the jar in a warm sunny area, and watch for roots to appear within a few days. Foliage appears in week or two and grows into an attractive vine.
Change the water every two to three days to prevent stagnation. Keep the water level consistent by adding fresh water as it evaporates.
Transplant to a pot once roots are established and vigorous growth appears.