The potato is a staple crop across the globe, providing a reliable source of nutrition. Many people confuse the term “seed potato,” assuming it refers to a small, conventional seed. A seed potato is not a botanical seed, but rather a specialized tuber used to propagate the plant. This method ensures the resulting harvest is an exact duplicate of the parent plant.
Defining the Seed Potato
A seed potato is a whole, small potato or a piece of a tuber used for planting. Since the tuber is an underground stem, using it for propagation is a form of asexual reproduction, also known as vegetative propagation. This differs distinctly from true potato seed (TPS), which results from sexual reproduction and is contained in the small fruit produced by the potato flower.
The potato surface features small indentations called “eyes,” which are dormant buds. When planted, these eyes sprout, sending shoots upward to form the new plant and roots downward. The resulting potato plants are genetically identical clones of the original parent tuber, ensuring desired traits like yield, flavor, and disease resistance are preserved.
Planting a seed potato provides the new sprout with a large food reserve, allowing for rapid and vigorous growth. True potato seeds, by contrast, produce genetic variation, which is beneficial for breeders but unsuitable for commercial farmers who require predictable, uniform crops.
Ensuring Quality: Certification and Disease Control
Vegetative propagation ensures genetic consistency but carries the risk of accumulating diseases over time. Since the new plant is a clone, any viruses or bacteria present in the original tuber pass directly into the new generation. For this reason, growers avoid using grocery store potatoes or uncertified harvests, as these tubers can harbor pathogens that severely reduce yields.
Serious diseases, such as Bacterial Ring Rot and Potato Virus Y (PVY), can spread rapidly through infected seed stock and remain in the soil. Bacterial Ring Rot is a zero-tolerance disease in most certification programs because it can survive on farm equipment and spread easily during cutting and planting. PVY, a mosaic virus transmitted by aphids, is a major concern because it can dramatically stunt plant growth and deform tubers.
To combat this, professional seed potatoes undergo a rigorous, multi-year certification process overseen by state or federal agencies. This process begins with laboratory-produced, disease-free plantlets grown from meristem tissue, a technique used to eliminate viruses. The resulting tubers are grown in a series of field generations with strict tolerances and regular inspections, often including post-harvest testing to check for latent viruses before planting season begins. Certification signifies that the seed lot has met these quality standards, protecting the health of the crop and the industry.
Preparing and Planting for Successful Growth
Before planting, many gardeners “chit” their seed potatoes by encouraging the tubers to sprout indoors first. This involves placing the potatoes in a cool, bright location, such as a windowsill, for four to six weeks before the last expected frost. The light exposure causes the eyes to produce short, stocky sprouts, which are much stronger than the pale sprouts that form in darkness. Chitting gives the plants a significant head start, resulting in an earlier and potentially larger harvest.
If a seed potato is larger than a hen’s egg, it can be cut into smaller pieces to maximize yield, provided each piece weighs at least two ounces and contains two healthy eyes. After cutting, the pieces should be left exposed to the air for one or two days in a humid environment. This crucial step allows the cut surface to dry out and form a protective, corky layer called a callus, which prevents the seed piece from rotting in the soil.
The seed pieces are ready for planting when the soil temperature reaches at least 45 degrees Fahrenheit, typically a few weeks before the last frost. They should be planted with the eyes facing up in trenches six to eight inches deep, spaced 12 to 15 inches apart. As the plant grows, soil is gradually mounded around the emerging stems, a practice known as hilling, which provides more surface area for new tubers to form.