Sweet potatoes are large tuberous root crops that grow underground, like standard potatoes, turnips, rutabagas and yams. Sweet potatoes are a warm-season crop, though, and require frost-free growing conditions. To lengthen the growing season and give sweet potatoes the time they need, many home growers choose to start the tubers indoors in early spring, for transplant into the garden as seedlings. Since sweet potatoes already hold all the growing material they need, this is a relatively straightforward process.
Fill a pint or quart jar, or standard glass, 3/4 full with fresh water. Poke three to four toothpicks into the side of a sweet potato to support it, then put the potato in the glass so that the bottom end of the potato is in the water while the top end is exposed.
Set the jar or glass in a place where it gets full sunshine for six to eight hours every day, and temperatures of at least 80 degrees F. Don't put the glass in a place where it gets hit by heating or air conditioning, as this will dry the sweet potato and damage its growth.
Maintain the water level in the glass to keep the sweet potato always at least partially submerged, and look for sweet potato shoots after one to two weeks. These shoots are soil-ready, so transplant them directly to the outdoor garden or 6-inch pots with quick-draining soil. Transplant sweet potato shoots outdoors only after all danger of frost has passed.