Sweet potato slips are the vegetative sprouts that grow directly from the tuber and are necessary for starting a new sweet potato plant. Unlike white potatoes, sweet potatoes must be propagated from these slips to ensure a healthy crop. This process of generating slips must take place indoors, generally six to eight weeks before the last expected frost date, allowing the young plants enough time to develop before being transplanted into the warm outdoor soil.
Planning and Selecting Potatoes
Starting the process requires careful timing and selection of the parent tuber. Begin the sprouting process about ten weeks before your target outdoor planting date, typically two to three weeks after the last frost when the soil temperature is consistently above 65°F (18°C). The sweet potato must be healthy, firm, and free of blemishes or mold, as disease can be passed to the new slips.
It is recommended to use an organic or untreated sweet potato, as conventional produce is often treated with sprout inhibitors that prevent slip growth. A single medium-sized sweet potato can yield ten to twenty usable slips. Once selected, gather a jar and toothpicks, or a shallow tray and seed-starting mix, depending on the method you choose.
Generating Slips Using the Water Method
The water method is a common way to generate slips, requiring a jar and toothpicks. Insert three to four toothpicks around the middle of the sweet potato, creating a support structure that allows the tuber to rest on the rim of the jar. The bottom third to half of the potato should be submerged in water, which encourages root growth from the submerged end and sprouts from the top.
Place the jar in a warm location, such as on a heat mat or a sunny windowsill, as sweet potatoes thrive in temperatures around 80°F (27°C) for sprouting. Change the water every few days, or at least once a week, to prevent mold or bacteria that could cause the potato to rot. Over four to eight weeks, small white roots will emerge, followed by green shoots, or slips, on the portion above the water line.
Alternative Method Using Soil Bedding
The soil bedding method involves using a shallow container or tray filled with a moist growing medium like seed-starting mix, peat moss, or sand. The sweet potato is laid horizontally and covered partially or completely with the mix, ensuring good contact between the tuber and the moist soil.
This setup should be kept consistently moist but not waterlogged to prevent rot, and placed in a warm environment, ideally with bright light or under a grow light. Warmth is important for stimulating growth buds; a temperature of 75°F or higher will accelerate the process. A benefit of this method is that the slips often develop roots while still attached, eliminating a separate rooting step later.
Harvesting, Rooting, and Hardening Off Slips
Once the slips are four to six inches long, they are ready to be harvested from the parent sweet potato. To remove them, gently twist the slip off where it emerges from the tuber, or use a clean, sharp knife to cut it away. Removing slips encourages the parent potato to produce a second flush of sprouts, extending your yield.
The detached slips should then be placed in a jar of water, ensuring the bottom node is submerged. Within a few days to a week, the slips will develop fine, white roots, a process sped up with warmth and bright light. When the roots are about an inch long, the young plants must undergo “hardening off,” which is the process of gradually acclimating them to outdoor conditions.
To harden off, place the rooted slips outside in a protected, shaded area for an hour or two, slowly increasing the time and exposure to direct sunlight and wind over seven to ten days. This introduction strengthens the plant and prevents transplant shock, preparing them for permanent planting once all danger of frost has passed.