Sweet potato slips are young sprouts grown from a mature sweet potato tuber, serving as the planting material for a new crop. This vegetative propagation method is the standard approach for cultivating sweet potatoes, ensuring the new plants are genetically identical to the parent tuber and preserving desirable characteristics. Using slips bypasses the need for true seed, which is unreliable and may not produce a plant true to the variety.
Selecting and Preparing the Tuber
The first step in generating healthy slips is choosing a high-quality sweet potato tuber, often called the mother potato. Select tubers that are organically grown or confirmed to be untreated, as conventional sweet potatoes are sometimes treated with sprout inhibitors that prevent the necessary shoot growth. The chosen tuber should be firm, smooth, and completely free of soft spots, mold, or signs of disease, which could introduce pathogens.
Avoid using sweet potatoes stored in a refrigerator, as cold temperatures below 55°F can cause internal damage, resulting in a hard core and hindering sprout production. Smaller to medium-sized tubers (around two inches in diameter) are preferred because they yield a higher number of slips than very large potatoes. Once selected, the tuber should be thoroughly washed to remove residual soil or debris before beginning the sprouting process.
The whole tuber can be used, or it can be cut into two or more sections to maximize the surface area for sprout emergence. If cutting, each piece must be substantial and contain at least one visible eye or bud. The cut surfaces should be allowed to air-dry for a few hours to form a protective callous before placement in the rooting medium.
Initiating and Maintaining Sprout Growth
Sprout growth can be initiated using either the water method or the generally faster soil method, both requiring warm, consistent conditions to signal the plant to begin growth. The water technique involves suspending the tuber in a jar or container with one end submerged, typically using three or four toothpicks inserted around the middle to rest on the rim. The pointed end of the sweet potato (often the stem end) should be placed in the water for better results.
For the soil-based method, the tuber is placed horizontally or cut in half and laid cut-side down in a shallow tray filled with a moist medium, such as potting mix, sand, or a mixture of both. The tuber is then covered lightly with one or two inches of the medium, ensuring the environment remains moist but not waterlogged. The soil method is preferred because the slips begin developing roots while still attached, eliminating a later rooting step.
Regardless of the method chosen, maintaining a warm and bright environment is necessary for successful sprouting. An ideal temperature range for encouraging sprout production is between 75°F and 85°F, which is warmer than typical room temperature. Placing the container near a sunny window or utilizing a plant heating mat helps achieve and maintain this warmth.
The setup should receive bright, indirect light, as excessive direct sun can overheat the container or cause the tuber to dry out or rot prematurely. If using the water method, the water must be changed every three to five days to maintain oxygen levels and prevent mold, algae, or bacterial rot. Sprouts typically emerge from the tuber’s surface within two to four weeks under these conditions.
Harvesting and Rooting the Slips
The sweet potato slips are ready for harvest once they have grown to six to eight inches tall and developed at least three or four sets of leaves. Allowing the slips to reach this size ensures they have enough stored energy and leaf surface area to begin photosynthesis independently. They should be removed gently from the mother potato to avoid damaging the sprout or the tuber.
The most common way to harvest is by twisting the slip off at its point of attachment or by carefully cutting it with a sharp, clean knife. Cutting allows for a cleaner separation, while twisting may pull a few small, undeveloped roots along with the slip, which can be advantageous. Any roots that developed directly from the slip while attached should be preserved.
Once removed, the harvested slips must be rooted before they can be planted in the garden. This is done by submerging the lower half-inch to one inch of the stem in a container of fresh water. Remove the bottom-most leaves to ensure no foliage is submerged, which could lead to decay and contaminate the water.
The containers holding the slips should be placed in a warm location out of direct sunlight, with the water changed every few days to keep it oxygenated. Roots emerge from the submerged stem within a few days. The slips are ready for the next stage when the roots are one to two inches long, which usually takes one to two weeks. Alternatively, the slips can be placed directly into a small pot of moist potting mix to develop roots.