How to grow sweet potatoes Plant your sweet potato sprouts in late may when the ground starts to warm up. You want to plant them about 8-10 inches a part. The sprouts can be purchased at a farm coop or at farm stores that handle supplies for gardening. The potatoes take about 5 months to become full grown. Around October you can go out with a shovel and begin digging around the sweet potato sprouts to find the potatoes. Make sure that you start back a few inches from the plant and work your way closer so that you don't split any of the potatoes when you go to dig them up. Once October arrives you can enjoy fresh sweet potatoes.