Sweet potatoes are a warm-weather crop that requires a long, hot growing season, making planting time the single most important factor for a successful harvest. Unlike traditional potatoes, sweet potatoes are extremely sensitive to cold and must be transplanted into the garden only after all danger of frost has passed. Getting the timing right ensures the plants establish quickly and have enough time to develop their edible storage roots before the season ends. Rushing the planting process can lead to stunted growth or crop failure.
The Golden Rule: Temperature and Frost Risk
The most significant factor determining the correct planting date is the temperature of the soil, not just the air. Sweet potato slips, which are the young plants used for transplanting, are highly susceptible to chilling injury and will not grow in cold soil. The absolute minimum soil temperature for planting is 60°F, but the plants establish better when the soil consistently reaches 65°F or higher. Planting should occur approximately three to four weeks after the average last spring frost date in your region. This delay allows the soil to absorb enough solar energy to reach the necessary warmth for the plant’s root development. Soil temperatures between 70°F and 80°F are ideal for growth.
The Pre-Planting Timeline: Starting Sweet Potato Slips
The outdoor planting date is preceded by an indoor preparation phase involving sweet potato slips. Slips are the rooted sprouts that grow directly from a mature sweet potato and are the starting material for the crop. Gardeners must begin sprouting these slips indoors about six to eight weeks before their target outdoor planting date. This timeline ensures the slips are between six and twelve inches long with a healthy root system when it is time to transplant them. Once the slips are ready and the soil temperature is appropriate, they must undergo a process called “hardening off.” This involves gradually acclimating the young plants to outdoor conditions, such as direct sunlight and wind, for about one to two weeks before they are permanently set in the garden.
Completing the Cycle: When to Expect Harvest
The final timing consideration is the length of the growing season required to produce a harvestable crop. Sweet potatoes typically need 90 to 120 days from planting until the roots are mature, though the exact time depends on the specific variety. Harvesting must be completed before the first expected fall frost, as cold temperatures can damage the developing storage roots. If a hard frost kills the vines, immediate harvest is necessary to prevent decay from traveling down to the roots. A visual cue that the roots are nearing maturity is when the leaves on the vines begin to turn yellow and die back.