How do you start a sweet potato plant?
How do you root a sweet potato?
Starting Sweet Potato Slips in Water 
Examine the sweet potato and determine which is the sprouting end—it will have more nodes or “eyes” than the opposite end. If you can’t tell, put the sweet potato in a warm room for a few days—the nodes should become more apparent.
Push three or four toothpicks into the sweet potato to hold the sprouting end above the water. 
Set the lower end (the rooting end) in a jar of water and wait for your slips to form. It may take several weeks.
 Detach them and place them in water where they will develop roots.