Sweet potatoes are a warm-weather crop, and successful cultivation depends on selecting the correct planting time. This tropical vegetable is extremely sensitive to cold, making Oklahoma’s climate a major factor in determining the ideal planting window. The goal is to maximize the long, hot growing season by observing specific environmental conditions.
Determining the Ideal Planting Window
Planting sweet potato slips must wait until the danger of spring frost has completely passed. Although the last expected frost in Oklahoma can be as early as mid-April, planting should be delayed considerably to ensure warmth. The critical factor is the soil temperature, which must be consistently warm for the slips to survive and grow vigorously.
Sweet potatoes require a soil temperature of at least 60 degrees Fahrenheit at a 2-inch depth, with an ideal temperature closer to 65 degrees Fahrenheit. Planting slips too early, when the soil is still cool, will stunt growth or cause the slips to rot before they establish roots. For most of Oklahoma, the correct planting time is from late May through early June.
This planting window ensures the young plants are not exposed to cold soil or nighttime temperatures, which should be above 55 degrees Fahrenheit. While sweet potatoes thrive in the Oklahoma summer heat, setting them out prematurely in the spring will significantly reduce the final yield. Waiting for the soil to naturally warm up results in a more productive growing season.
Preparing the Soil and Planting Site
Site preparation must be completed before the slips are planted to provide the ideal environment for the developing tubers. Sweet potatoes perform best in a loose, well-draining soil, with a sandy loam texture being recommended. This light composition allows the storage roots to expand easily, promoting smooth, well-shaped potatoes.
If the native soil is heavy or has poor drainage, creating raised beds or ridges is necessary to ensure aeration. These ridges should be formed to a height of about 8 to 10 inches and spaced approximately three feet apart to accommodate the sprawling vines. The elevated soil warms up faster in the spring and provides the excellent drainage that prevents root rot.
Sweet potatoes require a soil pH between 5.5 and 6.5. They require less nitrogen than many other vegetables, as high nitrogen levels encourage lush vine growth at the expense of root development. Fertilizing before planting should focus on phosphorus and potassium, using a blend like a 10-20-20 formula to support strong root initiation.
Harvesting and Curing for Storage
Sweet potatoes require a long growing period, generally maturing between 90 and 120 days after planting. The timing of the harvest is determined by the first autumn frost, as tubers must be dug before the soil temperature drops below 50 degrees Fahrenheit. A light frost that kills the vines signals it is time to harvest, but a hard frost can damage the tubers and reduce storage life.
The harvest process requires care, as the skin of a freshly dug sweet potato is delicate and easily bruised. Growers should use a garden fork and begin digging a foot or more away from the main stem to avoid damaging the developing tubers. After lifting the potatoes, allow them to dry for a few hours, and then gently brush off the excess soil without washing them.
The next step, curing, improves both flavor and storability. Curing involves keeping the potatoes in a warm, highly humid environment, ideally 85 degrees Fahrenheit with 85 to 90 percent relative humidity, for about four to ten days. This period encourages starches to convert into sugars, intensifying sweetness, and allows minor skin damage to heal for long-term storage.