Sweet potatoes are grown from slips, which are essentially transplanted young seedlings grown from seed potatoes. You can grow your own sweet potato slips for planting by either purchasing seed potatoes or saving starter roots from last year's crop. Because sweet potatoes can harbor a host of root diseases, purchase seed potatoes that are virus-indexed or certified to make your slips. Select a planting site for your seeds that has well-draining soil. You can dip the sweet potato seeds in a fungicide before planting them to help prevent them from rotting.
Prepare the seed bed in mid- to late spring, when the soil temperature is at least 60 degrees Fahrenheit. Remove all weeds, grasses and other debris from the planting site and till or break up the soil prior to planting.
Measure and mark rows that are 2 to 4 feet wide at the planting site using small flags or wooden stakes. Place the seed potatoes on the soil in the rows, spacing the seeds in each row about 6 to 12 inches apart.
Spread 2 inches of topsoil on top of the seeds. Broadcast a 10-10-10 NPK granular fertilizer on top of the planting bed at a rate of 3 pounds per 100 square feet.
Water the soil well to moisten it. Don't allow the water to pool or waterlog the soil.
Lay clear or black plastic sheeting over the seed bed. Use a knife or screwdriver to cut small holes into the plastic, ensuring that there are about two or three holes around each planted seed potato.
Remove the plastic sheeting when the seedlings begin to sprout and grow about 1 inch tall. Water the seedlings once or twice a week to supplement rainfall.
Harvest the sweet potato slips when the seedlings grow to about 12 or 15 inches tall. Select the strongest, healthiest-looking sprouts and cut them with sharp scissors, a knife or pruning shears about 1 inch above the soil surface. These are your slips.
Dig up all of the seed potatoes and roots after you've harvested the slips. Don't allow any vegetative debris from the seed potatoes to remain in the planting bed to prevent the spread of diseases.