Sweet potatoes are a warm-season root vegetable, distinct from the common white potato, which is a tuber. Unlike many garden vegetables, this crop is not typically grown from seeds but rather from specialized sprouts called “slips.” A slip is essentially a stem cutting that develops from the mature sweet potato, and successfully generating these is the foundational step for planting a sweet potato crop. The process of producing these slips requires specific conditions and timing, preparing the young plants for their eventual transfer to the garden.
Preparing the Tuber and Timing the Start
The initial step in growing slips involves selecting the correct parent sweet potato, known as the mother tuber. Choosing a healthy, firm, and blemish-free sweet potato is important for successful sprouting. It is recommended to use an organic tuber, as conventionally grown sweet potatoes are sometimes treated with sprout-inhibiting chemicals that slow or prevent slip formation.
If the sweet potato has been stored in a cold environment, allow it to warm up for a few days on a counter, as cold temperatures can reduce its ability to sprout. Timing the process is based on the last expected frost date in your region, since sweet potatoes are sensitive to cold soil. Slips need approximately six to eight weeks of indoor growth before planting outside, which should occur when the soil temperature consistently reaches 65 degrees Fahrenheit.
The Water Method for Sprouting Slips
The water method is a popular, visually engaging way to start the process of generating slips indoors. To prepare the tuber, place it in a glass jar or container, submerging roughly half of its body in water. This is often achieved by inserting three or four toothpicks around the middle of the potato to rest on the rim of the container, suspending the tuber.
The jar should be placed in a warm location that receives bright, indirect light, such as a sunny windowsill. Warmth is a strong factor in stimulating sprout growth, with ideal temperatures around 80 degrees Fahrenheit, though slips will grow at lower temperatures. Water needs to be replaced every few days to maintain freshness and prevent the waterlogged portion of the tuber from rotting or developing mold.
After a few weeks, small reddish sprouts will emerge from the upper surface, while fine roots form underwater. While simple, this technique often yields fewer slips and can take longer—up to eight weeks—compared to the soil-based alternative. If the submerged end begins to rot, cutting the tuber in half and submerging the other end can sometimes salvage the process.
The Soil Bedding Method
The soil bedding method is an alternative, often more efficient technique that replicates conditions used in commercial propagation. Start with a shallow tray or container filled partially with a moist, sterile medium like sand, peat moss, or potting mix. Lay the parent sweet potato horizontally onto the medium and lightly cover it, so only about half of the tuber is visible.
Keep this bedding container consistently moist but not saturated to prevent decay. Placing the tray on a heat mat or in a warm spot, such as on top of a refrigerator, helps accelerate the process by providing warmth. The soil method encourages faster growth and produces a greater number of robust slips than the water method.
Within a couple of weeks, small sprouts will push up through the soil, rapidly developing into leafy slips. Continuous contact with the soil medium allows the emerging slips to develop small roots directly on the parent potato. This direct rooting helps minimize transplant shock when the slips are separated and planted.
Harvesting and Hardening Off Slips
Once the slips reach four to six inches in height, they are ready to be separated from the mother potato. To harvest, gently twist or snap the slip off at its base where it emerges from the tuber. Ensure the harvested slip includes a small node, or connection point, as new roots will readily form in this area.
If the harvested slips lack visible roots, place them in a jar of water for a few days to encourage root development. Fine white roots usually emerge quickly, sometimes within a day or two, indicating they are ready for the next stage. Before planting the rooted slips directly into the garden soil, they must undergo hardening off.
Hardening off prepares the tender indoor-grown slips for the harsher outdoor environment, including direct sun, wind, and fluctuating temperatures. This transition involves gradually exposing the slips to outdoor conditions over about a week. Start by placing the slips in a shaded, protected area outdoors for a few hours each day, slowly increasing the duration and sun exposure. This acclimatization prevents sun damage and ensures the slips survive their final planting.