Sweet potatoes are a warm-season crop grown from rooted sprouts called slips, which are vine cuttings taken from a mature sweet potato. Successful cultivation relies on preparing the planting material and placing it into the garden when the soil has warmed sufficiently. This temperature-dependent timing ensures the heat-loving plants establish quickly and have a long enough season to produce a substantial harvest.
Preparing or Sourcing Sweet Potato Slips
Gardeners acquire slips by purchasing certified plant material or by sprouting their own from a mature sweet potato. Certified slips from a reputable nursery offer disease resistance and guarantee a specific variety. If propagating slips from a store-bought sweet potato, use organic tubers to avoid growth inhibitors applied to conventional produce.
To generate slips at home, the tuber can be bedded in soil or placed partially submerged in water. The soil method involves nestling the tuber halfway into moist potting mix or sand. The water method involves suspending the potato with toothpicks so the bottom half is in water, encouraging roots and sprouts to form.
Once the slips reach about six inches in length, gently twist or cut them away from the mother potato. The cuttings are often placed in water to develop a small root system. A hardening-off period is recommended, involving gradually exposing the young slips to outdoor conditions over a week before transplanting.
Determining the Optimal Planting Window
Planting sweet potato slips is entirely dependent on temperature, as these tender, tropical plants cannot withstand frost. The earliest planting window is typically three to four weeks after the last expected spring frost date. However, waiting for the correct soil temperature is a more reliable indicator of success than relying on a calendar date.
Sweet potatoes require warm soil to initiate growth and prevent the young slips from rotting. The minimum soil temperature for successful planting is 60°F, but the slips perform better when the soil reaches an ideal range of 65°F to 85°F. Many growers suggest waiting until the soil is consistently 70°F or higher, noting that planting below this threshold often causes crop failure.
Use a soil thermometer to take readings four inches deep for several consecutive mornings to confirm the ground is sufficiently warm. Nighttime air temperatures should also be reliably above 50°F, as cooler evenings stall growth. Planting too early can lead to poor yields because the slips struggle to establish roots and may succumb to disease in cold, damp soil.
Technique for Planting Slips
Once the soil temperature is confirmed, planting the slips must be done carefully to encourage high yields. Plant sweet potatoes into mounds or ridges of soil approximately six to eight inches high. This technique improves drainage, allows the soil to warm faster, and provides loose earth for the roots to expand without obstruction.
Slips should be spaced 10 to 18 inches apart within the row, depending on the variety. Planting depth is important because sweet potatoes form along the buried stem. Bury the majority of the stem, setting the slip three to six inches deep, leaving only the top two to four leaves exposed above the soil surface.
Planting in the late afternoon or on an overcast day minimizes transplant shock from intense sun and heat. The soil should ideally be loose and well-draining, but sweet potatoes grow in heavier soils amended with organic matter. Immediately after planting, gently firm the soil around the slip and water thoroughly.
Post-Planting Care and Harvest Timing
Consistent watering is necessary immediately after transplanting to help the slips establish new root systems and recover from shock. For the first week to ten days, generous watering is required. After this initial phase, sweet potatoes need consistent moisture, especially during dry periods, but they do not tolerate waterlogged conditions.
Sweet potatoes perform best in soil that is not overly rich in nitrogen, which encourages excessive vine growth instead of root development. If fertilization is needed, apply a low-nitrogen formula as a side-dressing three to four weeks after planting. As the vigorous vines spread, they naturally shade out weeds, reducing the need for weeding later in the season.
Harvest timing is determined by the specific variety, with most sweet potatoes requiring 90 to 120 days to reach maturity. A sign that the crop is ready is when the leaves and ends of the vines begin to turn yellow, signaling that the plant is slowing growth. Harvest must occur before the first expected fall frost, as cold soil temperatures below 50°F can damage the quality and taste of the roots.