How To :
- First, stick 3-4 toothpicks around the center of the sweet potato.
- Place it in the glass. the toothpicks should rest of the end of the glass holding the sweet potato up so it is not touching the bottom of the glass.
- Fill your glass up with water so about 1/3 to 1/4 of the sweet potato is submerged in the water.
- Anywhere from a few days to a week or two you should start to see roots sprout from the submerged part of the sweet potato.
- After a while longer, you should see stems (and if you leave it long enough, leaves sprouting out of the top.)
- Keep it in a warm sunny window and keep adding water as needed.
- Once you have a good amount of white roots established, you can leave it in a container of water or plant your potato in some soil. Sweet potatoes do well in all types of soil.
Source : How to Root a Sweet Potato for Planting