Getting the planting depth right for seed potatoes is crucial for a successful harvest. Potatoes are unique because the edible part, the tuber, grows above the planted seed piece, making it susceptible to light exposure. When tubers are exposed to sunlight, they turn green, producing a toxic compound called solanine, which makes them inedible. Proper depth also offers insulation, protecting the developing crop from early spring frost damage and providing the necessary space for the plant to form a substantial number of tubers.
Pre-Planting Preparation of Seed Potatoes
Preparing the seed potatoes before planting gives them a head start and encourages stronger, earlier growth. This process, often called chitting, involves encouraging sprouts to form before the seed piece is placed in the soil. To begin chitting, place the seed potatoes in a single layer in a bright, cool, and frost-free location, such as a garage or porch, for about four to six weeks at 50°F to 60°F (10°C to 15°C).
The light exposure ensures the sprouts that form are short, stocky, and dark green or purple, which are much stronger than the long, white, weak sprouts that develop in darkness. Before planting, inspect the chitted potatoes and remove all but the two to four strongest sprouts per seed piece. This selective removal focuses the plant’s energy on producing fewer, more vigorous stems, which often leads to a higher yield of larger tubers.
Larger seed potatoes should be cut into smaller pieces approximately two ounces in weight, ensuring that each piece contains at least one or two well-developed “eyes” or sprouts. After cutting, the pieces must be allowed to “cure” for two to three days in a humid, well-ventilated area, away from direct sun. This curing period allows the cut surface to dry out and form a protective, leathery callus, which significantly reduces the risk of rot and disease once the seed piece is underground. Planting the cured pieces with the cut side down and the sprouts facing up helps guide the developing shoots toward the soil surface.
Initial Planting Depth and Row Spacing
The initial planting depth is important and must be managed carefully for the health of the potato plant. Most growers plant the seed pieces in a shallow trench or individual hole that is approximately four to six inches deep. This depth provides immediate insulation against fluctuating early spring temperatures, including light frost, which can damage emerging foliage. It also leaves plenty of vertical space above the tuber for the necessary subsequent addition of soil throughout the season.
Potatoes should only be planted once the soil temperature is consistently above 45°F (7°C), as planting into cold, waterlogged soil can cause the seed pieces to rot before they can sprout. The soil must be loose and well-tilled, as tubers develop best in uncompacted conditions; deep planting into heavy, dense soil will hinder tuber formation. In-row spacing between individual seed pieces should be between 10 to 15 inches apart, allowing each plant adequate space to develop a robust root system and a full set of tubers.
The distance between rows is also a consideration, affecting both plant growth and ease of maintenance, particularly the practice of hilling. Rows are typically spaced 24 to 36 inches apart, which provides enough room to maneuver a hoe or tiller to draw up soil for hilling without damaging the plants. Closer spacing tends to produce a higher quantity of smaller potatoes, whereas wider spacing encourages the growth of larger, full-sized tubers. This initial burial is only the first step in maintaining the correct depth, as the plant will continue to demand more soil cover as it grows.
The Practice of Hilling to Maintain Optimal Depth
While the initial planting depth is important, the final, optimal depth of the developing tubers is achieved through the repeated action of hilling. Hilling is the process of mounding soil, compost, or straw around the base of the potato plant stems as they grow throughout the season. The primary biological reason for hilling is to prevent the developing potato tubers from being exposed to sunlight. Tuber exposure to light initiates the production of chlorophyll, which causes the green color, and the toxic alkaloid solanine, which renders the potatoes unfit for consumption.
The secondary benefit of hilling is that it encourages the plant to produce more tubers. Potato tubers form on specialized underground stems called stolons, and adding soil around the main stem stimulates the formation of more of these stolons, thereby increasing the overall yield. The first hilling should take place when the potato plants reach a height of about six to eight inches above the ground.
Using a hoe or shovel, draw loose soil from between the rows and pile it around the stems. The goal of each hilling application is to cover the stem, leaving only the top few inches of foliage exposed. This process must be repeated several times throughout the early to mid-growing season, typically every two to three weeks as the plant grows another six to eight inches. By the end of the season, the base of the plant should sit beneath a substantial mound of soil, ensuring that all developing tubers are fully protected from light and have maximum space for expansion.