Sweet potatoes are propagated from vegetative starts called “slips,” which are sprouts grown directly from the mature tuber, rather than from seeds. Making your own slips ensures you have healthy, vigorous planting material ready for the growing season. This process is the necessary first step for cultivating sweet potatoes and allows for the clonal propagation of the desired variety.
Selecting the Tuber and Necessary Supplies
Selecting the proper mother tuber is the first step in generating slips. Choose sweet potatoes that are firm, unblemished, and ideally purchased from an organic source or garden center to reduce the chance of growth inhibitors. Avoid tubers showing signs of mold, rot, or soft spots, as these may fail to sprout or introduce pathogens.
Gather a few simple supplies to facilitate the sprouting process. These include clear jars or containers, wooden toothpicks, and either clean water or a sterile growing medium, such as a potting mix or a mixture of peat moss and sand. Ensure all containers are clean to prevent fungal or bacterial contamination during the months-long process.
Sprouting the Slips: Step-by-Step Instructions
There are two primary methods for encouraging the mother tuber to produce sprouts: the water method and the soil method. For the water method, insert three or four toothpicks around the middle of the sweet potato and suspend one end in a jar of water, submerging about half of the tuber. The toothpicks prevent sinking and allow the submerged end to develop roots while the exposed end develops shoots.
Change the water every few days to maintain oxygen levels and prevent stagnation, which can lead to decay. Alternatively, the soil or sand method involves partially burying the sweet potato horizontally in a shallow tray filled with moist sand or potting mix, leaving about half of the tuber exposed. This method often results in more robust slips because the developing shoots are already rooted in a solid medium.
Warmth is paramount for initiating growth, as sweet potatoes are tropical plants. Maintain a consistent temperature range between 75°F and 85°F (24°C–29°C) for optimal sprouting, perhaps by placing the container on a heat mat or near a warm window. Once sprouts begin to emerge, the tuber requires bright, indirect light to ensure the slips grow short and stocky. Slips may begin to appear four to six weeks after the process begins.
Separating and Preparing Slips for Planting
Slips are ready for harvest when they reach four to six inches in length and have several leaves. To separate them, gently twist the slip off the tuber or use a clean, sharp knife to cut the shoot near the surface of the potato, ensuring a small piece of tuber skin remains attached. Cutting is preferred as it minimizes damage to the remaining slips on the mother potato.
After separation, the freshly harvested shoots must be rooted independently before transplanting into the garden. Place the cut end of the slip into a jar of water, submerging the bottom third of the stem. The stem will develop its own independent root system over the course of one to two weeks. Change the water frequently during this period to prevent bacterial growth and maintain oxygenation.
Once the slips have developed a dense mass of white feeder roots, they are ready for hardening off. This process acclimates the tender indoor-grown plants to outdoor conditions, including sunlight, wind, and cooler night temperatures. Over seven to ten days, gradually expose the rooted slips to increasing amounts of outdoor time, starting in shaded areas and moving toward full sun. This gradual exposure prevents scorching and reduces transplant shock.
When and How to Transplant Sweet Potatoes
Transplanting the hardened-off slips into the permanent garden bed must be timed carefully according to local climate conditions. Sweet potatoes are sensitive to cold and should only be transplanted after all danger of frost has passed in the spring. The soil temperature is a more accurate indicator than air temperature, and it should consistently register at least 60°F (16°C), though 65°F (18°C) is preferred for rapid establishment.
To plant the slips, set them deep into the prepared soil, burying the stem up to the top set of leaves. This depth encourages the formation of storage roots along the buried section of the stem. For maximizing yield, space slips 12 to 18 inches apart in rows that are three to four feet apart.
Immediately after planting, provide a deep watering to settle the soil around the new roots and reduce transplant shock. Maintaining consistent moisture for the first week is beneficial while the slips establish themselves in the warm garden bed.