A method I used for propagating an ornamental sweet potato was one I heard a gardener say he used for edibles. I had stored a huge tuber from 'Margarita', and the following spring placed it horizontally in a shoe box sized container, covered with moist potting soil. When the sprouts reached 4-6" in length, I pulled them off the tuber and planted them. When I had all I needed, I put the whole thing in a planter. You can get lots of plants from one tuber! That's how I plan to start next years plants.