Sweet potatoes are grown from a rooted cutting known as a slip, not from a seed or by planting the root directly into the garden. A slip is the young vine growth that emerges from a mature sweet potato root when exposed to warm, moist conditions. Cultivating these sprouts allows a gardener to turn a single sweet potato into a large yield of new roots or a decorative houseplant vine. This process is the fundamental first step in sweet potato propagation.
Selecting the Tuber and Initial Setup
The first step is selecting the right sweet potato, which is technically a storage root. Opting for an organically grown sweet potato is recommended because conventionally grown roots are often treated with a sprout inhibitor. This chemical treatment prolongs shelf life but significantly reduces the chance of successful growth.
Once a healthy root is chosen, the environment must be warm to encourage growth. Sweet potatoes require sustained warmth, with an ideal temperature range for sprouting between 75°F and 85°F. The root should also be placed in a bright location, such as a sunny windowsill or under a grow light, to stimulate shoot development.
For the water method, suspend the sweet potato in a container. Insert three or four toothpicks around the middle of the root to act as a support, allowing the bottom third to sit submerged in water. If choosing the soil method, the root is laid on its side and covered halfway or entirely with a moist growing medium, such as potting soil or sand.
Encouraging Slip Growth: Water and Soil Methods
There are two primary methods for encouraging the sweet potato root to produce slips. The water method requires the submerged portion of the root to be kept consistently in fresh water. Change the water every three to five days to keep it oxygenated and prevent mold or bacteria growth, which can cause the root to rot.
The water approach typically takes longer, with slips ready for harvest in about six to eight weeks. The soil method is often preferred for efficiency, as it can cut the time needed for slip emergence in half, sometimes yielding sprouts in three to four weeks. In this method, the root is bedded in a container of loose, moist soil and kept warm and bright.
A benefit of the soil method is that the slips often begin to form small roots while still attached to the parent root. Whether using water or soil, the environment must maintain a consistently warm temperature, as any prolonged chill will halt the sprouting process. The parent root can continue to produce multiple rounds of slips as long as it remains healthy and is kept in favorable conditions.
Harvesting and Transplanting the New Vines
The slips are ready for harvest when they reach four to six inches long and have developed several sets of leaves. To remove the new growth, gently twist the slip away from the root, or use a clean, sharp blade to cut it off near the point of attachment. Slips grown in soil may already have tiny roots attached, which provides a significant head start.
Slips removed without roots must undergo a rooting phase before they can be planted in soil. Place the cut end of each slip into a jar of water, ensuring the bottom node is submerged while the leaves remain above the water line. New, fine white roots should begin to emerge from the submerged stem within a few days.
The rooted slips are ready for transplanting once the new roots are about an inch long. For an ornamental vine, plant the rooted slip into a pot with fresh potting mix. For an edible crop, transplant the slip into a garden bed after the last frost, ensuring the soil temperature is at least 65°F. Plant the slip deep enough to cover the new roots and at least one or two nodes on the stem, as new storage roots will form at these buried points.