Sweet potatoes are enlarged storage roots from the vine Ipomoea batatas, a member of the morning glory family, and are not true potatoes. The ultimate yield of these roots is highly dependent on environmental factors and specific cultivation methods, leading to significant variation. Understanding these variables is the first step in maximizing your harvest potential.
Typical Harvest Expectations
A home gardener can generally expect an average harvest of between 1.5 and 3 pounds per plant. This estimate is based on common spacing practices, such as planting slips 12 inches apart in a row. This spacing often results in 15 to 30 pounds of roots from a 10-foot row. Commercial operations, which use optimized fertilization and irrigation systems, often achieve much higher yields, sometimes producing over 35,000 pounds per acre.
This variation highlights the difference between commercial and backyard growing, as commercial systems are designed for peak efficiency. Most individual plants will produce approximately three to five harvestable storage roots. These roots vary widely in size, from small fingerlings to large jumbos, which directly influences the final weight per plant.
Key Variables Determining Plant Output
The most significant factor influencing the final weight is the choice of cultivar. Some varieties, like ‘Beauregard,’ are specifically bred for high yield, while others prioritize flavor or disease resistance. Selecting a variety well-suited to your local growing conditions can immediately boost your expected output.
Sweet potatoes thrive in well-drained, light, sandy loam soil, preferring a pH between 5.5 and 6.6. Heavy clay or excessively rich soils restrict the expansion of storage roots, resulting in long, stringy, or misshapen potatoes and a lower yield. Planting the slips in raised mounds or ridges helps ensure necessary drainage and provides loose soil for the roots to expand freely.
The spacing of the plants also directly affects the size and number of roots developed. Planting slips too far apart can lead to fewer, but large, “jumbo” roots, which may not be the ideal size for consumption. Conversely, planting too closely may result in a higher number of roots that remain too small.
Sweet potatoes are a warm-season crop requiring a long, frost-free period, typically between 90 and 120 days, to reach full maturity. Optimal root development requires warm soil temperatures, as growth slows considerably when the soil temperature drops below 60°F. A shorter growing season limits the time the plant has to bulk up its storage roots, which directly reduces the final weight harvested.
Securing the Final Usable Weight
Post-harvest processing is necessary to secure the final usable weight for long-term storage. The timing of the harvest is important, as the roots must be dug before the soil temperature drops below 50°F, which causes internal damage and affects storability. Harvesting is typically done after the leaves begin to yellow, around 80 to 130 days after planting, but always before a hard frost hits the ground.
After harvest, the sweet potatoes must undergo curing for long-term preservation. Curing involves holding the freshly dug roots at high temperature and high humidity for several days. This requires maintaining conditions of 85°F with 90 to 95 percent relative humidity for four to seven days.
This high-heat, high-humidity environment promotes the healing of minor cuts or bruises sustained during digging, forming a protective layer of wound cork. Curing also initiates the conversion of starches into sugars, enhancing the characteristic sweetness and flavor. Without proper curing, the roots are highly susceptible to disease and rot, reducing the amount of usable food.
Following curing, the sweet potatoes should be moved to a cooler environment for long-term storage. The ideal conditions are a temperature range of 55°F to 60°F with 85 to 90 percent relative humidity. Storing them below 55°F can cause chilling injury, leading to a hard center, discoloration, and off-flavors. When properly cured and stored, the harvest can remain viable for four to seven months.