how long do you bake sweet potatoes in oven
1 Don't preheat the oven. 2  Prick your sweet potatoes each 2-3 time with a fork, then place them directly on the oven rack in the middle of the oven, above the foil. 3  Turn the oven on to 425. 4  Bake for 45 minutes for sweet potatoes/yams that are 2-3 inches in diameter.