Sweet potatoes are grown from vegetative cuttings called “slips,” not by planting the whole root directly like a regular potato. Slips are the sprouts that grow from the mature sweet potato. These miniature plants, which have leaves and developing roots, are the only viable way to start a new crop. The cultivation process begins indoors, well before the last spring frost, by encouraging a healthy sweet potato to produce these necessary sprouts.
Preparing Slips for Planting
Creating the slips is the first step in growing sweet potatoes, and this process should begin eight to twelve weeks before the intended outdoor planting date. The traditional “water method” involves suspending a healthy, untreated sweet potato halfway in a jar of water using toothpicks.
Change the water regularly to prevent rot, and place the jar in a warm, sunny location to encourage sprouts to emerge. The “soil method” is often faster and more reliable, involving placing the sweet potato horizontally and partially covered in moist potting soil. Placing this container on a heat mat or in a warm spot significantly speeds up sprouting, often cutting the time needed in half.
When sprouts reach four to six inches, carefully remove them from the parent potato by gently twisting or cutting them where they emerge from the root. Remove the lower leaves from the detached slip. Place the slip in a glass of water for one to two weeks to develop a healthy network of roots several inches long. These rooted slips are then ready for transplanting once the weather is consistently warm.
Essential Environmental Conditions
Sweet potatoes are a tropical crop that demands a long, hot growing season. They are sensitive to cold, so planting must be delayed until the danger of frost has passed and the air and soil are sufficiently warm. A soil temperature of at least 65°F, measured four inches deep, is the minimum required for successful transplanting and growth.
For optimal development, plants need full sun, ideally a minimum of eight hours of direct sunlight daily. Soil composition is a defining factor in the quality of the harvest. Sweet potatoes thrive in light, loose, and well-draining soil, with a sandy-loam texture being the most favorable for forming smooth, well-shaped roots.
Avoid overly rich soils, particularly those with high levels of nitrogen. While nitrogen promotes lush vine growth, excessive amounts cause the plant to prioritize foliage development over producing underground storage roots. Focus instead on soils with moderate levels of phosphorus and potassium to encourage robust root formation.
Planting Techniques and Maintenance
Once the soil is warm and prepared, the next step is planting the rooted slips. To ensure good drainage and help the soil warm up faster, create raised mounds or ridges about eight to ten inches high and a foot wide. These mounds provide the loose environment developing roots need to expand easily into large storage roots.
Plant the slips by burying the stem deep enough so that at least two nodes (small bumps where roots emerge) are underground, leaving a few leaves exposed. Space the slips twelve to fifteen inches apart along the top of the mounds, with rows spaced three to four feet apart to accommodate the sprawling vines. Immediately after planting, water the slips thoroughly to help them settle.
Plants require consistent and deep watering, especially during the first fifty to sixty days while establishing root systems. While mature plants tolerate dry spells, providing one inch of water per week during drought significantly improves the harvest yield. The vigorously growing vines naturally shade out most weeds, minimizing the need for constant cultivation, though careful weeding around the base of young slips is necessary initially.
Harvesting and Curing
Harvest typically occurs after a 90 to 120-day growing period, or when the foliage begins to turn yellow in the fall. The most reliable trigger is the first light frost, which signals the end of the growing season. It is important to harvest before the soil temperature drops below 55°F, as cold soil can cause internal decay in the roots.
Harvesting requires a careful approach to avoid bruising the thin, easily damaged skin of the storage roots. Use a garden fork to gently loosen the soil several inches away from the main stem, then carefully lift the entire root cluster. Once dug up, brush off any large clumps of soil, but do not wash the sweet potatoes, as moisture can encourage rot.
The final step before storage is the two-part process of curing and storing, which enhances the sweet potato’s flavor and longevity. Curing involves holding the roots at 80–90°F and 80–90% humidity for four to fourteen days. This process allows nicks and bruises to heal with a corky layer. Crucially, curing converts starches within the root into natural sugars, providing characteristic sweetness. Following curing, move the roots to a dark, ventilated storage area at 55–60°F, where they can last for many months.