Sweet potatoes are a warm-season crop propagated from specialized cuttings called “slips,” rather than seeds or pieces of the tuberous root like traditional potatoes. A slip is a shoot, complete with leaves, grown directly from a mature sweet potato. The process of propagation involves coaxing a healthy, whole sweet potato to sprout these green shoots indoors several weeks before the outdoor planting season. This method allows home gardeners to grow a greater number of plants from a single parent sweet potato and provides a head start on the growing season.
Preparing the Tuber and Initiating Slips
The initial step is selecting a healthy, non-treated sweet potato, preferably organic, since commercial tubers may have sprout inhibitors applied. Sprouting requires warmth and uses two primary indoor methods: water or soil. Both approaches stimulate the dormant buds, or “eyes,” on the tuber’s surface by providing necessary moisture and temperature.
The traditional water method involves suspending the sweet potato in a container of water, often using toothpicks to keep the bottom half submerged. Place the container in a warm, brightly lit location, such as a sunny windowsill. This method can take four to eight weeks for the slips to reach a usable size.
The soil method is often faster and more reliable, involving partially or fully burying the sweet potato horizontally in damp soil or sand. Keep this container consistently moist and warm, ideally between 75°F and 85°F, which can be achieved with a heat mat. Shoots will emerge within three to four weeks, and the parent sweet potato can continue to produce multiple rounds of slips for several weeks.
Harvesting and Hardening Off the Slips
Slips are ready for harvest once they reach four to six inches long and have developed a few leaves. To separate them from the parent sweet potato, gently twist or carefully cut the shoots near where they emerge from the tuber. Remove any leaves that would be submerged or buried, as this prevents decay and focuses the plant’s energy on root production.
The newly harvested slips must be placed in water or a sterile potting mix to encourage root system growth. If placed in water, submerge the base of the slip; roots typically form rapidly, sometimes within just a few days. Alternatively, plant the slips directly into small pots of soil to establish a more robust root ball before final planting.
Once the slips have developed a healthy set of roots, they must undergo “hardening off” before moving permanently outdoors. This involves gradually acclimating the young plants, which have been coddled indoors, to the harsher elements of the garden, including direct sunlight, wind, and temperature fluctuations. Over seven to ten days, place the slips outside for progressively longer intervals, starting with an hour in a shaded area and slowly increasing exposure to full sun. This methodical transition strengthens the plant and significantly improving its survival rate once transplanted.
Transplanting Slips to the Garden
The hardened sweet potato slips are ready for their permanent location only after the danger of frost has completely passed and the soil temperature has warmed sufficiently. Sweet potatoes are highly sensitive to cold, so planting must be delayed until the soil consistently maintains at least 60°F to 65°F. Planting too early in cool soil can severely stunt growth and reduce the final yield.
Sweet potatoes perform best in light, sandy, and well-draining soil that allows the storage roots to expand easily. To further encourage this development, plant the slips on raised rows or mounds, which helps the soil warm faster and improves drainage. These mounds should be about eight to ten inches high and spaced approximately three feet apart.
When planting, insert each slip so the roots and the lower two to three nodes of the stem are completely covered, leaving the leaves exposed. A typical spacing of 12 to 18 inches between slips on the mound is recommended to give each plant enough room to develop. Water the slips immediately after planting to settle the soil around the roots, and maintain consistent moisture for the first week or two while the plants establish themselves.