One way to grow sweet potatoes is from the roots of the previous season's crop. Growing sweet potatoes from the roots of the previous season ensures that the sweet potatoes are acclimated to your growing zone, something you cannot be certain of when starting sweet potatoes from store-bought potatoes.
Sweet potatoes like warm soil and warm temperatures, so it may be best to start plants indoors. They can be started directly in the garden as long as all possibility of frost has passed and the soil is warm.
Mix two parts sand and one part loam into a growing tray, if starting your sweet potatoes indoors. If starting them outdoors, plant them directly in soil that has had two handfuls of loam mixed into it. Sweet potatoes can grow in almost any type of soil as long as it is warm and well drained.
Choose a fresh sweet potato and cut it in half lengthwise. Plant each half in the growing tray, rounded side down, or place each half in a sunny part of your garden, rounded side down. Sprinkle half an inch of sandy soil over the tops of the tubers and water well.
Keep the growing tray in a warm location, between 21.1 and 26.6 degrees C, and keep the soil moist but not soaking wet. No fertiliser is required, although a handful of loam every week will encourage more active growth. Green shoots, known as slips, should appear in two to three weeks. When the slips have three to four healthy-looking leaves, they are ready to be separated.
Use a sharp knife to carefully remove the slips from the main tuber. Each slip will have its own roots attached. Take the roots along with the slip. The parent tubers will continue to produce more slips for most of the growing season.
Plant the sweet potato slips in the same soil and loam mixture that you used to start your slips. Just cover the roots and allow the rest of the vine to remain above ground. If planting outside, be sure there is no possibility of frost and allow at least 9 inches between each plant. The plants will spread vines as they grow.
Keep the ground damp but not saturated. Sweet potatoes like plenty of sun and damp but well-drained sandy soil.
Allowing your tubers to be in direct sun for 6 to 8 hours a day may produce stronger slips with more developed root systems. Sweet potato vines will root as they spread, so the plant can be considered invasive. Keep vines trimmed and growing only in the desired areas of your garden. Sweet potatoes are tropical plants, so northern growers may wish to keep their plants in pots that can be moved indoors as the weather cools.