The sweet potato is often mistaken for a true tuber, like the common white potato, but it is actually a distinct root vegetable. The edible part of the plant is an enlarged storage root, a structure that forms from the plant’s lateral roots, rather than a modified stem called a tuber. Growing sweet potatoes depends on meeting their specific environmental demands. They are an unfussy crop, provided the grower can supply a long, uninterrupted season of sustained heat. This tropical plant needs a growing period of 90 to 120 days, with consistently warm air and soil temperatures above 65 degrees Fahrenheit, which is the primary challenge for gardeners in cooler regions.
Starting the Crop with Slips
Sweet potatoes are not grown from seed or from planting a piece of a root, but from plant sprouts known as slips. These slips are young vine cuttings that can be purchased from a specialized nursery or grown at home by suspending a mature root in water or burying it in moist sand. Starting with certified, disease-free slips is a recommended preventative measure against common pests and diseases.
Planting should occur approximately three to four weeks after the last expected spring frost, once the soil has warmed sufficiently. The planting bed should be prepared by incorporating organic matter and mounding the soil into ridges about eight to ten inches high. This mounding technique ensures the soil drains well and allows the developing storage roots ample space to expand.
The crop thrives in lighter, well-draining soil, ideally a sandy loam, with a slightly acidic pH between 5.8 and 6.2. Heavy clay soil can restrict root expansion, often resulting in misshapen or smaller storage roots. Slips are planted about twelve to eighteen inches apart on the prepared ridges, with the base of the slip buried deep enough to cover the lowest leaves.
Essential Care and Maintenance Requirements
Once planted, the sweet potato requires a long period of sustained heat, with optimal air temperatures in the 80s, and is highly sensitive to cold, which can damage the roots below 50 degrees Fahrenheit. The plant’s care centers on patience and management of soil conditions. Proper water management is important during the early stages of growth, as the plants are sensitive to drought for the first fifty to sixty days after transplanting.
After establishment, the plants become drought-tolerant, though consistent, deep watering during dry spells helps maximize yields. Avoid over-fertilizing the plants, particularly with high-nitrogen formulas, because this encourages lush vine growth at the expense of root development. A low-nitrogen, high-potassium fertilizer is applied a few weeks after planting to support the forming roots.
The long vines that spread across the ground should not be pruned or cut back, as this reduces the energy available for the roots below the surface. The most destructive pest is the sweet potato weevil, which tunnels through the roots, making them inedible. Preventing this pest involves cultural practices like crop rotation and hilling up the soil around the base of the vines.
Knowing When and How to Harvest
Sweet potatoes are ready for harvest three to four months after planting, but they must be dug up before the first hard frost. Frost damages the vines and negatively affects the quality and storage life of the roots if they remain in cold soil. Gardeners look for signs of maturity when the leaves begin to yellow toward the end of the growing season.
The digging process requires care, as the skin of the sweet potato is thin and easily bruised or scraped by a shovel or fork. Cut the long vines back first, and then use a garden fork placed well away from the center of the plant to gently loosen the soil. The roots should be lifted carefully, handling them as little as possible to avoid damage.
After harvest, the roots must undergo curing to develop sweetness and ensure a long storage life. Curing involves holding the unwashed roots at 80 to 85 degrees Fahrenheit with high humidity, around 90 percent, for four to fourteen days. This warmth allows the skin to heal from small nicks and converts starches into the sugars that give the sweet potato its characteristic flavor.