The best way to grow sweet potatoes is to plant slips, little shoots that sprout from the eyes of a sweet potato. Purchase slips at a nursery, or grow some by cutting a healthy sweet potato in half and submerging the pieces halfway in water or placing the sweet potato at a 45 degree angle in warm, moist soil. Once the slips or sprouts grow at least 6 inches tall, carefully twist them off of the potato, and plant them.
To encourage root growth before planting the slips, place them halfway in water, and wait for the roots to develop to the desired length. Plant the sweet potato slips by preparing the gardening site. Till the top foot of soil, and amend it with compost if necessary to improve drainage. Loose soil is necessary for the roots to grow well.
Starting in the spring after the last frost, dig a 4-inch-deep hole in the soil, and place the roots, along with 1/2-inch of the stem, in the hole. Fill in the hole with soil, and give the plants a mixture of water and high-phosphorus starter fertilizer. Water the slips well and often. After the first month, feed the plants a 5-10-10 ratio fertilizer, and continue to water them well throughout the growing season.