The sweet potato is botanically classified as a root tuber, a swollen storage structure derived from the plant’s roots. While you technically can plant a whole sweet potato, it is an inefficient method that rarely leads to a successful harvest in a home garden. Planting the entire root often results in a single, crowded plant that struggles to produce multiple, sizable roots. The most effective way to cultivate sweet potatoes is by planting specialized cuttings called “slips.”
Why Sweet Potatoes are Grown from Slips
Using slips, which are the sprouted shoots of the sweet potato, maximizes yield and plant health. Planting a whole root forces all emerging shoots to compete for limited space and nutrients, often resulting in a poor harvest. The mother potato can also rot in the ground before the plant establishes, potentially leading to disease issues in the new growth.
A single sweet potato, when properly sprouted, can yield dozens of individual slips. Each slip grows into a new, separate plant capable of producing multiple harvestable roots. This method allows for the creation of many plants from one parent root, significantly increasing the potential harvest. Slips are transplanted after the soil has warmed, bypassing the cold, damp conditions that would cause a whole sweet potato planted in early spring to decay.
Sprouting Sweet Potatoes to Create Slips
To begin the process, force a mature sweet potato to sprout indoors, starting about six to eight weeks before the target outdoor planting date. This is done using one of two methods: suspending the root in water or burying it partially in a moist medium. The traditional water method involves inserting toothpicks into the sides of the sweet potato and resting it over a jar of water, keeping one end partially submerged.
The preferred method is the soil or sand bedding technique, where the whole or halved sweet potato is nestled into a tray of moist seed-starting mix, with about half the root covered. The sweet potato needs warmth and light to encourage sprouting. Ideal conditions for rapid sprouting are high temperatures, between 75°F and 85°F, and a bright location, such as a sunny window or under a grow light.
Once the shoots, or slips, reach four to six inches long, they are ready to be harvested from the parent root. For water-sprouted slips, the shoot is broken off and placed in water to develop its own roots. Slips grown in a soil bed often already have roots forming and can be gently pulled or sliced from the mother potato. The separated slips are allowed to root fully in water or moist soil for about a week before being prepared for the garden.
Transplanting and Cultivation
Sweet potatoes are a tropical plant, and transplanting slips requires warm soil temperatures, ideally consistently above 60°F. Gardeners should wait until at least two weeks past the last expected frost date to ensure the soil has adequately warmed, as cold soil below 55°F can severely damage the young plants. Preparing the outdoor bed involves forming mounds or hills of loose, well-drained soil, which encourages the formation of the storage roots and prevents waterlogging.
The rooted slips should be planted deep enough so that at least two to three nodes—the small bumps on the stem where leaves emerge—are buried beneath the soil surface. This buried portion of the stem generates the new storage roots that become the sweet potatoes. Slips are spaced approximately 12 to 18 inches apart on the prepared hills, allowing each plant enough room for its long, vining growth.
After planting, the slips must be thoroughly watered and kept consistently moist for the first week to establish. Once established, sweet potatoes are drought-tolerant but benefit from about an inch of water per week to ensure a large harvest and prevent the roots from cracking. The plants require a long, warm growing season, typically 90 to 120 days, before the roots are ready for harvest in the fall.