Sweet potatoes are not grown from seeds or pieces of the tuberous root like white potatoes. Instead, they propagate from sprouts that grow directly off the parent root, which are called slips. These slips are stem cuttings that, when rooted and planted, will grow into new sweet potato plants. This method is necessary because the sweet potato is a storage root, not a true tuber. This guide provides a step-by-step process for preparing and planting these sprouts to ensure a successful harvest.
Generating Sweet Potato Slips
The initial step is encouraging a mature sweet potato to produce sprouts, starting 8 to 12 weeks before the planned outdoor planting date. Gardeners typically use one of two indoor methods to force the growth of these slips, both requiring warmth and light.
Water Method
The traditional approach involves suspending the sweet potato halfway in a jar of water using toothpicks. The lower half must remain submerged. While simple, this method can take six to eight weeks or longer for slips to form.
Soil Method
A more efficient technique is the soil method, which often cuts preparation time to four to six weeks. Partially bury the sweet potato in a tray of moist sand or potting mix, covering about half of the root. Keep the container in a warm area, ideally between 75°F and 85°F, and provide bright light.
Regardless of the method, keep the medium consistently moist. Wait until the emerging slips are about three to six inches long before harvesting them.
Preparing Slips for Transplanting
Once the sprouts reach the appropriate length, separate them from the parent root to prepare them for rooting. Harvest slips by gently twisting, snapping, or cutting the stem near the surface of the root. If the slip is removed without roots, immediately place the cut end in a jar of water to encourage development. Remove lower leaves to prevent rot, and change the water weekly to keep it fresh.
Within one to two weeks, the slips will develop fibrous roots several inches long, indicating they are ready for the next stage. Before permanent outdoor planting, the rooted slips require hardening off to acclimatize them to the garden environment. This involves gradually exposing the young plants to increasing periods of direct sunlight, wind, and cooler outdoor temperatures over about a week. Hardening off strengthens the plant tissue and reduces transplant shock.
Planting Slips in the Garden
The timing for planting sweet potato slips is dictated by temperature, as they are highly sensitive to cold and require warm conditions to thrive. Wait until all danger of frost has passed and the soil temperature, measured at a depth of four inches, is consistently above 60°F; 65°F is optimal for strong root development. Sweet potatoes require full sun for at least six to eight hours daily and loose, well-draining, slightly sandy soil. Raised beds or mounding the soil into eight-inch-high hills improves drainage and soil warming.
When preparing the planting site, incorporate organic matter, but avoid heavy applications of nitrogen fertilizer. High nitrogen encourages excessive vine growth rather than edible storage roots. Plant the slips deep into the prepared soil, burying the stem so at least two nodes are beneath the surface. Only the top few leaves should remain exposed, as new sweet potatoes form along the buried nodes of the stem. Space the slips approximately 12 to 18 inches apart.
Initial Care and Establishment
Immediately after transplanting, a thorough and deep watering is necessary to settle the soil around the roots. This initial heavy watering eliminates air pockets and ensures close contact between the roots and the soil. For the first week, keep the soil consistently moist to support rapid root system establishment, as newly planted slips are vulnerable to drought.
After the first week, reduce the watering frequency, aiming for about one inch of water per week. Consistent moisture is important for the first 50 to 60 days. Apply a layer of organic mulch, such as straw or shredded leaves, around the plants to retain soil moisture and suppress weeds. Monitor the young plants for common pests, such as sweet potato weevils, and apply a low-nitrogen fertilizer only if soil tests indicate a deficiency.