Ipomoea batatas, or sweet potato vines, are cultivated for their edible tuberous roots and striking ornamental foliage. Whether a variety is bred for culinary purposes (like ‘Beauregard’) or for decorative leaves (like ‘Blackie’), the propagation technique is the same: growing sprouts called “slips” from the tuber. This process allows a single sweet potato to yield multiple plants, providing an economical way to start a garden. The following steps detail how to transform a simple store-bought or saved tuber into a flourishing vine ready for the garden.
Sprouting the Tubers to Produce Slips
The first step in vine propagation is encouraging the tuber to produce sprouts, or slips, which act as the cuttings for new plants. Selecting a healthy, unblemished tuber is important. Choosing an organic sweet potato is recommended because non-organic varieties may be treated with sprout inhibitors, and they require warm conditions to initiate growth.
Two common methods exist for forcing these slips: the water glass method and the soil bed method. For the water method, the sweet potato is suspended in a jar with toothpicks so that the bottom third is submerged in water, encouraging root formation. The soil bed method involves burying the tuber halfway in moist potting soil or sand, which often results in faster and more vigorous slip development.
Regardless of the technique, the tuber needs consistent warmth, ideally between 70°F and 80°F, and bright light. Sprouts will begin to emerge from the nodes, or “eyes,” after about four to six weeks. Once the sprouts reach four to six inches in length and have several leaves, they are ready to be carefully detached from the mother tuber.
Rooting and Preparing Slips for Planting
The next stage involves transforming the sprouts into self-sufficient, rooted cuttings. Each slip should be carefully removed from the mother sweet potato with a clean twist or sharp cut, ensuring no piece of the original tuber remains attached. Slips are best removed when they are at least six inches long, providing enough stem for successful rooting. The process of rooting the slips before planting significantly increases the rate of survival and establishment in the garden.
To encourage root growth, the base of the slip is placed into a jar of clean water, or inserted into moist, sterile potting mix or vermiculite. If using the water method, change the water every few days to prevent bacteria and rot. Within a week or two, small white feeder roots will become visible at the submerged end, signaling that the cutting is ready for transplanting.
Transplanting the Rooted Vines
Sweet potato vines should not be moved outdoors until all danger of frost has passed and the soil temperature consistently registers at least 65°F. Before planting, the young slips must be gradually introduced to outdoor conditions, a process called “hardening off,” which prepares them for direct sun and wind.
Hardening off involves placing the slips outside in a protected, shaded area for short periods, increasing their exposure time over one to two weeks. The final planting location should provide full sunlight for maximum growth and should have loose, well-draining soil. If the native soil is heavy clay, planting on raised beds or hills ensures proper drainage.
When transplanting, the rooted slips should be planted about two to three inches deep, ensuring that two or more nodes on the stem are buried beneath the soil surface. Spacing the slips 10 to 14 inches apart allows enough room for the vigorous vines to spread and for the tuberous roots to develop.
Long-Term Care and Harvesting
Once the sweet potato slips are established in the garden, they require consistent care. Immediately after planting, the young vines must be thoroughly watered, and the soil should be kept consistently moist until the plants are visibly established. After this initial period, the vines are drought-tolerant, but deep watering of about one inch per week during dry periods is beneficial.
Fertilizing sweet potato vines requires a balanced approach; if the primary goal is a tuber harvest, a low-nitrogen fertilizer is preferred three to four weeks after transplanting. Excessive nitrogen will encourage leafy vine growth rather than root development. The dense foliage helps to suppress weeds.
Harvest typically occurs 90 to 120 days after the slips were planted, or before the first hard frost. To prevent damage to the potatoes, the vines should be cut back a few days before digging, and a garden fork should be used to gently loosen the soil 12 to 18 inches away from the main plant.