Potatoes are not grown from true botanical seeds, but rather from a piece of the tuber itself, known as a seed potato. Cutting larger seed potatoes into smaller pieces is a common practice used to maximize the number of potential plants from a limited supply of tubers. This division ensures each resulting plant grows from a viable bud, or “eye,” which increases the overall yield.
Preparing the Seed Potato for Division
The journey to a successful potato harvest begins with selecting certified, disease-free seed potatoes that are firm and show no signs of rot or mold. Starting with healthy stock is important because potatoes are susceptible to various soil-borne and tuber-borne pathogens that can quickly spread throughout the planting area. Tubers that are smaller than a hen’s egg are generally planted whole, while larger ones are candidates for division.
Before cutting, many gardeners choose to “chit” or pre-sprout their potatoes by exposing them to cool temperatures and indirect light for several weeks. This process encourages the dormant buds to break and form short, sturdy, dark-colored sprouts. The light exposure prevents the growth of the long, weak, white sprouts that typically form in dark storage conditions. Activating these sprouts allows the grower to clearly identify the most viable “eyes,” making the cutting process more efficient and ensuring each piece has a growth point.
The tubers should be warmed to room temperature for a day or two before cutting, especially if they have been stored in a cold environment. Warmer tissue responds better to the wound created by the cut, promoting a quicker, more robust healing process. Handling the tubers gently during the chitting and warming phases protects the newly formed sprouts, which are surprisingly fragile.
Proper Technique for Cutting Seed Pieces
The size of each resulting seed piece is the most important consideration during the cutting process, as it determines the amount of stored energy available to the emerging plant. Each cut piece should ideally weigh between 1.5 and 2.5 ounces, which is roughly the size of a small golf ball or a large hen’s egg. This size range offers a balance between maximizing the number of pieces and providing sufficient food reserves for vigorous initial growth.
It is important to ensure that each piece contains a minimum of one to two healthy, visible eyes, though two to three eyes are often preferred to increase the chances of successful sprouting. The eyes are concentrated at the “rose” end of the potato, which is the blunter, opposite end from where the tuber was attached to the plant stem. When dividing a large potato, the cuts should be made to distribute these eyes evenly across the resulting pieces.
The tool used for cutting should be a sharp, clean knife to facilitate smooth, blocky cuts that heal quickly. Using a dull instrument can tear the tissue, which leaves a rougher surface that is more vulnerable to infection from pathogens in the soil. It is a good practice to sanitize the cutting tool frequently, especially when moving from one potato to the next, to avoid the transmission of latent diseases between tubers.
For a very large tuber, it may be divided into three or four pieces, but the cuts should always aim to create chunky, block-like pieces rather than thin, flat, or wedge-shaped slices. Thin pieces, sometimes called “slabs” or “slivers,” dry out too quickly and lack the necessary mass to support the plant until the roots are established. When handling smaller seed potatoes that are still larger than the 1.5-ounce minimum but only have a few eyes, it is often better to plant them whole rather than risk division.
Callousing Cut Pieces Before Planting
After cutting, seed potatoes must undergo a curing period, often called callousing or suberization. This step allows the freshly cut, moist surfaces to dry and form a protective layer. The process involves the formation of suberin, a waxy, cork-like material that seals the wound.
This protective seal prevents excessive moisture loss from the seed piece and acts as a physical barrier against decay-causing bacteria and fungi present in the soil. Without this layer, the exposed, starchy interior is highly susceptible to rotting, especially if the planting soil is cool and damp. Callousing increases the survival rate of the seed pieces once they are in the ground.
To facilitate proper callousing, the cut pieces should be kept at a cool room temperature, ideally between 60°F and 70°F, with relatively high humidity. They should be spread out in a single layer on a clean surface, such as newspaper, cardboard, or a shallow tray, to ensure good air circulation around all sides. The pieces should be kept out of direct sunlight, which could dry them out too quickly or cause them to overheat.
This curing period typically takes about one to three days, depending on the temperature and humidity of the storage area. The cut surface should develop a tough, leathery, and dry texture, indicating that the protective layer has successfully formed. Once the pieces are properly calloused, they are ready for planting.