Sweet potatoes (Ipomoea batatas) are storage roots belonging to the morning glory family, distinct from true yams. Unlike standard potatoes, sweet potatoes are propagated vegetatively using specialized sprouts called “slips.” This method is necessary because planting the whole root directly often results in poor yields or the spread of disease. Successfully growing this warm-season crop requires generating and nurturing these slips before transplanting them into the garden.
Generating Sweet Potato Slips
The first step is generating the slips using a whole, healthy sweet potato. Two common methods facilitate the sprouting process, both requiring consistent warmth, ideally between 75°F and 85°F. Adequate light exposure, such as placing the potato near a south-facing window, encourages faster sprout development.
One popular approach involves the water method, where the potato is suspended in a container with one-third of its body submerged. Toothpicks are often inserted horizontally around the middle to balance it on the container rim. The water should be changed every few days to maintain oxygen levels and prevent mold or rot.
Alternatively, the soil method involves partially burying the sweet potato in a container filled with moist potting mix. Approximately half of the potato should remain exposed above the soil line to monitor sprout growth. This method tends to produce slightly more robust slips because the sprouts develop in a nutrient-rich environment.
Slips typically begin to emerge from the eyes of the potato after about four to six weeks. A healthy slip is a vine-like sprout, usually several inches long, featuring several small leaves. These sprouts need to reach a length of at least six inches before they are ready for the next stage.
Separating and Rooting the Slips
Once the slips have achieved the appropriate length, they must be cleanly separated from the parent potato. Instead of tearing them off, use a sharp, clean knife or shears to cut the slip where it meets the potato surface. This clean separation helps prevent the transmission of diseases from the mother root to the new plant.
After cutting, prepare the slips for rooting by placing the bottom portion of the stem into a jar of clean water, ensuring at least one leaf node is submerged. The water should be kept fresh, and the jar placed in a bright location out of direct sunlight. Fine white roots will emerge from the submerged nodes within one to two weeks, signaling the slips are ready for planting.
Before moving the rooted slips to the garden, “hardening off” is recommended to minimize transplant shock. This involves gradually introducing the young plants to outdoor conditions, starting with a few hours a day in a shaded area. Over the course of a week, slowly increase the duration and intensity of sun exposure, preparing the slips for the harsher environment of the garden bed.
Planting and Growing Requirements
Sweet potatoes are a tropical crop, demanding high soil and air temperatures for successful tuber development. Planting should only occur well after the last expected spring frost, typically when the soil temperature consistently reaches 60°F or higher. Planting into cool soil will stunt growth and reduce yields.
The ideal soil structure is loose, sandy, and well-draining, allowing the storage roots to expand easily. Compacted or heavy clay soils inhibit proper root formation, resulting in misshapen or small potatoes. Gardeners often plant slips into raised mounds or ridges, 8 to 10 inches high, which improves drainage and soil warming.
When transplanting the rooted slips, set them deep into the prepared soil, burying the stem up to the top set of leaves. Space plants 12 to 18 inches apart in rows three to four feet apart, allowing ample room for the extensive vine growth. The vines will spread rapidly, forming a dense canopy that naturally suppresses weeds later in the season.
Consistent watering is beneficial during the initial establishment phase to help the young roots take hold. Once established, sweet potatoes are relatively drought-tolerant but benefit from deep watering during dry spells when the tubers are expanding. They require a long growing season, generally between 90 and 120 days, to produce a harvest.
Nutrient management should focus on avoiding excessive nitrogen, which promotes vine growth at the expense of root development. A balanced, low-nitrogen fertilizer applied at planting supports healthy growth. Consistent weed control is important early on until the vigorous vines cover the ground and shade out competing plants.
Harvesting and Curing for Storage
Readiness for harvest involves observing the plant’s foliage, which naturally begins to yellow and die back as the season concludes. Harvest must occur before the first hard frost, as cold temperatures can damage the roots and reduce their storage life. Use a garden fork, starting about 18 inches away from the main stem, to carefully loosen the soil and lift the potatoes, minimizing bruising or puncturing.
After digging, the roots require a post-harvest treatment known as “curing,” which is essential for flavor development and long-term preservation. Curing involves holding the sweet potatoes at a high temperature, around 85°F, and high relative humidity (85 to 90 percent) for one to two weeks. This process heals minor wounds and initiates the enzymatic conversion of starches into sweeter, more palatable sugars.
Following curing, the sweet potatoes are ready for long-term storage in a cool, dark, and dry location, ideally maintained between 55°F and 60°F. Proper storage conditions allow the roots to be kept for many months. Stored potatoes should be checked periodically, and any showing signs of spoilage must be removed to prevent contamination.