The sweet potato (Ipomoea batatas) is a vining plant that produces a starchy, sweet-tasting storage root. It is a root vegetable and a member of the morning glory family, Convolvulaceae. The vast majority of sweet potatoes are grown asexually from “slips,” which are vine cuttings that act as clones of the parent plant. This standard practice explains why the average gardener rarely encounters the true botanical seeds, though the plant does have the capacity to produce them.
The Distinct Appearance of Sweet Potato Seeds
True sweet potato seeds are small, comparable in size to a peppercorn or a small grain of coarse sand. They possess a characteristic angular shape, frequently appearing irregular, teardrop-like, or slightly flattened. This morphology is common among seeds of the Ipomoea genus. The seeds display a dark coloration, typically ranging from a deep, mottled brown to black. They possess an extremely hard outer shell, or seed coat, which serves as a protective barrier against external conditions. This hard coat presents a challenge to germination that must be overcome before the seed can sprout.
The Botanical Process of Seed Formation
Sweet potato plants are considered short-day plants, requiring day lengths of less than 11 hours to initiate bloom. This explains why they do not readily flower in many temperate regions. When conditions are met, the plant develops funnel-shaped flowers that resemble those of the morning glory, often appearing in shades of white or lavender. These flowers open before sunrise and typically close and wither within a few hours, necessitating quick cross-pollination. Sweet potatoes exhibit a high degree of self-incompatibility, meaning they require pollen from a genetically distinct plant to set seed. Once successfully pollinated, the flower gives way to a small, dry, round fruit known as a seed capsule. This capsule is two-chambered, and each chamber has the potential to hold two seeds, resulting in a maximum of four seeds per fruit. However, it is more common to find only one to three viable seeds developing. The seeds mature within this capsule approximately four to six weeks after pollination, and the capsule will dry out and turn brown when the seeds are ready for harvest.
Growing Sweet Potatoes from True Seed
The primary reason commercial growers and home gardeners avoid using true seed is the high level of genetic variability it introduces. Unlike slips, which produce a genetically identical clone, a seed is the result of cross-pollination and will yield a unique, genetically diverse seedling. This means a seed from a high-yielding, orange-fleshed variety may produce a plant with purple flesh, low yield, or an undesirable flavor. This genetic lottery is why true sweet potato seeds are primarily used by plant breeders who seek to develop entirely new varieties with improved traits. For growers utilizing seeds, the first step is overcoming the seed’s hard coat to allow water absorption and germination. This process, known as scarification, involves physically nicking the seed coat with a sharp tool or gently rubbing it with sandpaper. Following scarification, seeds are typically soaked in water for several hours to soften the coat further and initiate the germination process. Even with these steps, the germination rate can be inconsistent, and the overall timeline from planting to a harvestable root is significantly longer compared to planting pre-sprouted slips. This extended growth time and the unpredictable characteristics of the resulting root stock reinforce why vegetative propagation via slips remains the industry standard for consistent and reliable sweet potato production.