Sweet potatoes are propagated from special cuttings called “slips,” not from the root itself like a regular potato. A slip is a sprout or vine cutting that grows directly from the whole sweet potato, carrying the exact genetic makeup of the parent plant. Since sweet potatoes originate from tropical and subtropical regions, a long, warm growing season is necessary for the roots to mature fully. The process begins indoors several weeks before the last expected frost to create the plant starts necessary for a successful harvest.
Starting the Sweet Potato Slips
Initiating the slips involves encouraging the parent root to sprout in warm, humid conditions, ideally between 75 and 85 degrees Fahrenheit. A popular method is the “water method,” where the sweet potato is partially suspended in a jar of water using toothpicks, ensuring a portion of the root remains submerged. Place the jar in a bright location, such as a sunny window, and change the water every few days to prevent stagnation.
An alternative is the “soil method,” where the whole sweet potato is laid horizontally and buried in moist sand or a soilless growing mix. This method often encourages faster sprouting, with slips appearing in three to four weeks, compared to four to eight weeks for the water method. Once the sprouts reach four to six inches long and have developed a few leaves, they are ready to be separated from the mother root. The slips should be carefully twisted or broken off at the base rather than cut.
Transitioning Slips to Soil
After removal from the mother sweet potato, the slips must develop their own root systems before permanent planting. Place the base of each slip into a jar of clean water, submerged deep enough to cover the lowest leaf nodes. Small white roots will begin to emerge from the submerged stem within one to two weeks, indicating the slip is ready for the next phase.
Once the roots are about an inch long, the slips must undergo “hardening off.” This gradual process prepares the tender, indoor-grown plants for the harsher outdoor environment, including direct sun and fluctuating temperatures. Hardening off involves slowly introducing the rooted slips to the outdoors over seven to ten days. Start with a few hours in a sheltered, shaded location and incrementally increase the time and sun exposure to prevent transplant shock.
Planting and Ongoing Care
Sweet potato slips should not be planted until all danger of frost has passed and the soil temperature is above 65 degrees Fahrenheit, with 70 degrees being optimal. The planting location requires full sun, ideally receiving eight to ten hours of direct light daily. Sweet potatoes thrive in loose, well-draining, and slightly sandy soil, which allows the storage roots to expand easily.
Avoid high-nitrogen fertilizers, as these promote vine growth at the expense of tuber development; phosphorus and potassium are more beneficial for root formation. Plant the slips 12 to 18 inches apart, burying the stem deep enough so only the top few leaves remain above the soil line. Planting on raised mounds or ridges, eight to ten inches high, warms the soil faster and improves drainage. While establishing, the plants require consistent moisture, but once the vines are fully established, they are relatively drought-tolerant.
Harvesting and Curing the Tubers
Sweet potatoes require a growing period of 90 to 120 days from planting until the tubers are ready for harvest. The roots are nearing maturity when the leaves on the vines begin to yellow, or ideally, just before the first expected hard frost. Harvest before the soil temperature drops below 55 degrees Fahrenheit, as cold soil can damage the flavor and storage quality of the roots.
Harvesting must be done carefully to prevent bruising or cutting the skin. Use a garden fork, starting 12 to 18 inches away from the main stem, to gently loosen the soil and lift the tubers without piercing them. Immediately after harvest, the sweet potatoes must undergo a curing process to convert starches to sugars and heal minor skin injuries. The tubers are held at a high temperature (80 to 85 degrees Fahrenheit) with high humidity (80 to 95 percent) for four to fourteen days. This controlled environment hardens the skin for long-term storage and enhances sweetness and flavor.