Sweet potatoes (Ipomoea batatas) are a warm-season crop belonging to the morning glory family. The edible part of the sweet potato is a storage root, not a true tuber like a potato. This crop requires a long, uninterrupted growing period with high temperatures to form its edible roots. Sweet potatoes are grown from small vegetative cuttings called slips, not true seeds.
Determining the Optimal Planting Window
The timing for planting sweet potatoes is entirely dependent on meeting the plant’s requirement for warmth. The most important factor is the soil temperature, which must be consistently warm for the slips to survive and establish roots. Planting should only occur once the soil temperature is at least 65°F, measured at a depth of four inches, and ideally warmer, reaching 70°F or higher for optimal growth. Planting too early into cool soil can cause the slips to become stunted or rot.
The second condition is that all danger of spring frost must have passed, as young slips are highly sensitive to cold damage. Nighttime air temperatures should also reliably remain above 55°F to prevent thermal shock. These conditions typically align about three to four weeks after the final expected frost date in a region.
Sweet potatoes require a long, frost-free period, generally ranging from 90 to 150 days depending on the variety, to reach full maturity. Growers must assess their climate to ensure the slips are planted early enough to allow full maturation before the first expected fall frost.
Sourcing and Preparing Sweet Potato Slips
Sweet potatoes are grown from slips, which are the sprouts that emerge from a mature sweet potato. Gardeners can purchase certified disease-free slips from a reputable nursery or start their own at home. Starting slips indoors should begin approximately six to eight weeks before the planned outdoor planting date.
To start slips, a mature sweet potato can be partially submerged in water or nestled partially in moist potting soil. Placing the sweet potato in a warm, bright location encourages the development of shoots. Once the shoots are five to six inches long, they are carefully removed from the parent sweet potato. These shoots can be placed in water to develop roots if they have not already formed.
Before moving the young plants to the garden, they must be gradually acclimated to outdoor conditions in a process known as hardening off. This involves exposing the rooted slips to increasing durations of sunlight and wind over about a week. Hardening off strengthens the slips, reducing transplant shock and improving their chances of successful establishment.
Planting Techniques and Establishment
Once the soil temperature is warm enough and the slips are hardened off, they are ready for planting into a prepared bed. Sweet potatoes perform best when planted into raised mounds or ridges, which should be six to eight inches high. This practice allows the soil to warm up more quickly and ensures excellent drainage, encouraging storage root development.
The slips should be spaced approximately 12 to 18 inches apart within the rows, with three to four feet between rows to accommodate the sprawling vines. Each slip needs to be planted deeply, burying the majority of the stem so that only the top two or three leaves remain above the soil line. This depth ensures that multiple nodes on the stem are covered. Storage roots will form at these buried nodes.
After planting, the slips must be watered heavily and immediately to settle the soil around the stem and roots and minimize transplant shock. Consistent moisture is necessary for the first week or two until the slips are visibly established and beginning to grow new foliage. This initial deep watering ensures a strong start to the long growing season.