Sweet potatoes are a delicious and highly productive crop that requires a unique propagation method compared to many other garden vegetables. Unlike traditional potatoes, which are grown from sections of the tuber itself, sweet potatoes are cultivated from small plant cuttings called “slips.” Understanding the nature and appearance of these slips is the first step toward a successful harvest.
Defining the Sweet Potato Slip
A sweet potato slip is a sprout or vine cutting taken from a mature sweet potato tuber. This method is a form of clonal propagation, meaning the resulting plant is a perfect genetic copy of the parent sweet potato. Slips are the standard way to grow the crop because planting the entire tuber or pieces of it, as done with white potatoes, can often lead to the tuber rotting in the soil before it can properly sprout. This process is distinct from using seeds, which would introduce genetic variation and produce unpredictable results.
Visual Characteristics of a Ready Slip
A healthy, ready-to-plant sweet potato slip should display several distinct physical attributes that signal its readiness for the garden. The ideal length for a slip is between 6 to 12 inches, providing enough stem to bury and still have foliage above ground. The stem should look robust and have a fresh, green to reddish-purple color, depending on the variety. A mature slip will have several nodes, which are the small bumps along the stem where leaves and roots emerge.
For successful establishment, a slip should have at least four to six leaves present at the top. The most telling characteristic is the presence of small, white, fibrous roots extending from the nodes along the portion of the stem that was submerged or buried. While slips without roots can still be planted, those with an established root system tend to establish themselves faster in the garden soil. Slips that arrive wilted or without roots are resilient and will develop quickly with proper care.
Generating Slips from a Tuber
The process of generating these plantlets from a sweet potato tuber begins six to eight weeks before the intended planting date. Two common methods are used to encourage the tuber to sprout slips: the water method and the soil bed method. The water method involves suspending a whole or cut sweet potato partially in water. This is a popular technique, but it can take eight weeks or more for the slips to reach a usable size.
The soil or sand bed method is preferred for producing rooted slips more quickly. This technique involves burying the sweet potato in a shallow tray of moist potting mix or sand and placing it in a warm location. For both methods, warmth and light are necessary, with ideal temperatures for sprouting being in the range of 70 to 85 degrees Fahrenheit. Once the sprouts appear, they are carefully twisted or cut from the parent tuber when they reach the desired length.
Preparing and Planting the Slip
Once the slips are removed from the parent tuber, they must be prepared for the transition to the garden. It is helpful to “harden off” the slips by gradually exposing them to outdoor conditions over several days, preparing them for the sun and wind. Before planting, the lower leaves on the stem should be removed to reduce moisture loss and ensure the leaves will not be buried in the soil. Slips are planted deep, with at least two-thirds of the stem, including the nodes where roots will form, placed below the soil surface.
The slip should be planted with the leaves above the soil line and the roots pointing downward into the prepared bed. Immediately after planting, a thorough watering is necessary to settle the soil around the stem and roots. Sweet potatoes are sensitive to cold, so planting should only occur when the soil temperature is consistently above 65 degrees Fahrenheit.