Sweet potatoes are warm-weather tubers grown from “slips,” which are vine cuttings or sprouts that develop from the mature storage root. Unlike standard potatoes, sweet potatoes cannot be planted whole. This technique of vegetative propagation is necessary because planting the tuber directly into cool soil often results in rotting rather than growth.
Essential Preparation: Timing and Tuber Choice
The process of starting slips indoors should begin approximately six to eight weeks before the anticipated outdoor planting date. Sweet potatoes should not be transplanted until the soil temperature consistently registers above 60°F, which is often two to four weeks after the last expected frost. Starting slips too early can result in leggy, overgrown plants that are difficult to manage and harden off effectively.
Selecting the right mother tuber is the first step in successful slip production. Use sweet potatoes that are certified seed stock or organically grown, as conventionally grown tubers may have been treated with sprout inhibitors. Look for firm, blemish-free potatoes without signs of bruising or decay, since a diseased mother tuber can pass pathogens to the developing slips. Medium-sized tubers, around two inches in diameter, are the most efficient for sprouting.
Initiating Growth: Step-by-Step Methods for Sprouting
Two primary methods are used to encourage the tuber to sprout: the classic water suspension technique and the faster soil bed method. The water method involves suspending a whole sweet potato in a jar of water, typically using three or four toothpicks to keep half the tuber submerged. The water level must be maintained so the bottom half remains wet, and the water should be changed every few days to prevent stagnation and rot.
The soil method, which often yields slips more quickly, involves laying the tuber horizontally in a shallow tray filled with a moist growing medium like sand or seed-starting mix. The sweet potato should be partially or fully covered with about an inch or two of the medium, ensuring the growing environment is kept consistently moist but not waterlogged. For both techniques, providing adequate warmth is necessary for growth initiation.
Sweet potatoes require high temperatures to break dormancy and sprout effectively, with an ideal range between 75°F and 85°F. Placing the container on a seedling heat mat is beneficial for maintaining this temperature, especially when using the soil method. Once sprouts emerge from the tuber (which can take four to eight weeks), the setup requires bright light to encourage stocky, healthy growth. A sunny window or a dedicated grow light positioned just above the sprouts will prevent them from becoming thin and weak before harvesting.
Preparing Slips for the Garden: Harvesting and Rooting
Once the sprouts, or slips, reach a length of four to six inches and have several leaves, they are ready to be separated from the parent tuber. The most sanitary way to harvest the slip is to carefully cut it from the potato using a clean, sharp knife or razor blade. Ensure no part of the original sweet potato is taken with the cutting, as this practice avoids transmitting potential diseases that might be present in the storage root to the new plant.
The freshly harvested slips must then be rooted before planting in the garden. Place the bottom two-thirds of the slip into a jar of clean water, ensuring the leaves remain above the waterline. The rooting process is typically quick, with small white roots beginning to form within a few days to one week. Changing the water every few days helps keep the environment fresh and oxygenated, supporting vigorous root development.
When the new roots are well-developed and several inches long, the slips are ready for hardening off. This process involves gradually acclimating the rooted slips to outdoor conditions, including direct sunlight and wind, before they are permanently transplanted. Begin by placing the slips outside in a sheltered, shaded location for short periods. Increase the time and exposure to full sun over a period of about seven to ten days. This transition prevents shock and leaf burn, ensuring the young sweet potato plants are robust enough to thrive once set into the warm garden soil.