The sweet potato, a tuberous root distinct from the common white potato, is a warm-weather crop that requires a specific, multi-stage agricultural process for commercial production. This systematic process is designed to maximize yield and ensure the quality of the final product. The journey from root to market involves specialized propagation, careful field management, and a post-harvest treatment essential for long-term storage and flavor development. The commercial cycle focuses on precision and environmental control to deliver a consistent product to consumers.
Starting the Crop: From Mother Root to Slips
Commercial sweet potato production uses vegetative sprouts called “slips,” not seeds. This propagation method is necessary because sweet potatoes are genetically diverse, and growing from seed would not reliably produce the desired commercial traits. Growers select perfect specimens from the previous harvest, known as “mother roots,” and place them in specially prepared beds, often within greenhouses or hotbeds.
These mother roots are typically pre-sprouted at warm temperatures, around 75 to 85°F, with high humidity for two to four weeks. Once bedded in soil or compost, they are covered and kept warm and moist to stimulate the growth of slips. The goal is to produce a high volume of vigorous sprouts genetically identical to the selected mother root.
Slips are ready for harvest when they are approximately six to eight inches long and possess four to six leaves. Growers harvest these sprouts by carefully cutting them just above the soil line to minimize disease transmission. This process allows the mother root to continue producing subsequent flushes of slips over a four-week period, ensuring a steady supply of planting material.
Field Planting and Managing Growth
The delicate slips are transplanted into the production field once the soil temperature consistently reaches at least 65°F and all danger of frost has passed. Commercial fields are prepared with raised beds or ridges to ensure the loose, well-drained soil environment sweet potatoes prefer. This ridging provides the necessary depth for storage roots to develop uniformly and helps prevent waterlogging, which can cause cracking and rot.
Slips are planted deep into the ridges, often using specialized mechanical transplanters, ensuring at least two nodes are buried for root formation. The sweet potato requires a long growing season, typically 90 to 150 days, depending on the variety and target size. Since the plants are highly sensitive to competition, growers maintain aggressive weed control for the first six weeks until the canopy closes.
A unique management practice is “vine turning,” where sprawling vines are periodically lifted to prevent them from rooting at the nodes. If rooting occurs, the plant produces numerous small, undesirable roots instead of channeling energy into the large storage roots needed for commercial sale. Consistent, but not excessive, watering is maintained throughout the season, with reduced irrigation late in the season to encourage skin set and prevent splitting.
Harvesting and the Critical Curing Process
Harvest timing is determined by assessing the size of the roots and the condition of the plant, not a fixed calendar date. Growers test dig a few plants to confirm the majority of roots have reached the desired marketable size, known as U.S. No. 1 grade. The harvest must be completed before the soil temperature drops below 55°F or before the first hard frost, as cold injury causes internal discoloration and poor storage quality.
Commercial harvesting is typically done mechanically using specialized equipment, such as a chain digger, which undercuts the roots and lifts them onto a conveyor. This machinery requires careful operation because the skin of a freshly harvested sweet potato is thin and easily damaged. After being gently sorted in the field to remove excess soil and initial culls, the highly perishable roots are transported immediately to a curing facility.
The critical post-harvest step is curing, a controlled process that heals wounds and converts starches into palatable sugars. This involves holding the sweet potatoes at 85°F to 90°F with 90% to 95% relative humidity for four to seven days. The high heat and humidity stimulate the formation of a corky layer beneath any damage, which prevents moisture loss and blocks the entry of decay organisms.
Grading and Maintaining Quality in Storage
Once curing is complete, the sweet potatoes are slowly cooled and prepared for long-term storage or immediate market distribution. The final step before shipping is grading, where the roots are sorted according to strict standards based on size, shape, and freedom from defects. Roots meeting the requirements for U.S. No. 1 are uniform, well-shaped, and bring the highest market price.
Properly cured sweet potatoes are then moved into storage facilities designed to maintain quality over several months. Unlike many other vegetables, sweet potatoes cannot be stored in cold temperatures, which causes chilling injury, resulting in internal breakdown and a disorder called “hardcore.” The ideal long-term storage environment is a dark, cool, and humid space, maintaining temperatures between 55°F and 60°F and a relative humidity of 80% to 90%.
These specific conditions slow the respiration rate of the roots and inhibit sprouting, allowing the sweet potatoes to be marketed year-round. Consistent ventilation is maintained to prevent the buildup of carbon dioxide, which accelerates spoilage. This controlled environment ensures the sweet potatoes retain their healed skin and enhanced sweetness until they are washed, packed, and shipped.