The potato is a popular garden crop, valued for its high yields. Successfully growing abundant and safe potatoes relies heavily on controlling the depth of the developing tubers. Proper planting depth ensures the seed piece is protected from frost and provides space for initial root development. Maintaining a sufficient soil layer above the potatoes prevents light exposure, which triggers the production of solanine, a natural toxin that causes the tubers to turn green.
Preparing for Potato Success
A successful potato harvest begins with the selection of certified, disease-free seed potatoes. These are specially grown to ensure they are free from common viruses and pathogens that can devastate a crop. To give the plants a head start, many gardeners utilize a process called chitting, or pre-sprouting, approximately six weeks before the anticipated planting date. This involves placing the seed potatoes in a cool, bright, and frost-free location with the “rose end,” the side with the most eyes, facing upward.
Chitting encourages the development of sturdy, dark-colored sprouts rather than the long, pale ones that form in darkness. For larger tubers, you can cut them into pieces roughly two inches square, ensuring each piece contains at least one or two healthy eyes. After cutting, the pieces must be allowed to cure for one to three days in a humid, well-ventilated space until the cut surfaces form a dry, protective callus. This callous layer helps prevent the seed piece from rotting once it is placed in the soil.
Planting should occur when the soil temperature consistently reaches 45°F, typically a few weeks before the last expected frost date. The ideal soil for potatoes is loose, deep, and well-draining, such as a sandy loam. It is beneficial to test the soil pH, as potatoes prefer slightly acidic conditions (5.0 to 6.0 range), which helps to minimize the occurrence of the common scab disease.
Initial Burial Depth and Spacing
The initial planting depth balances early emergence with protection for the seed piece and developing roots. A common method is to dig a trench or furrow six to eight inches deep. The seed potato pieces, with their cured cut surface down and eyes pointed up, are then laid into the bottom of this trench. This trench method is effective because it sets the stage for the progressive covering of the plant throughout the growing season.
The seed pieces should be spaced 10 to 15 inches apart within the trench to allow room for the formation of multiple tubers. If you are planting multiple rows, the trenches should be separated by 30 to 36 inches to provide space for hilling and air circulation. Once the seed pieces are positioned, they are covered with only three to four inches of loose soil, leaving the trench partially unfilled. This initial covering depth provides frost protection and insulation while allowing the young sprouts to emerge quickly.
Planting the seed piece three to four inches deep into a six-to-eight-inch trench is a foundational step for successful cultivation. The roots establish themselves in the soil beneath the seed piece, while the developing subterranean stem grows upward through the remaining empty space in the trench. This subterranean stem is where the stolons, the specialized underground stems that swell to become new tubers, will form, making the subsequent process of hilling possible.
Managing Depth Through Hilling
Unlike most vegetables, the tuber does not develop from the root system but instead forms along the stolons that sprout from the underground stem. This growth habit necessitates hilling, which is the process of continually adding material around the base of the plant as it grows. The primary purpose of hilling is twofold: to encourage a greater number of stolons to form, thereby increasing the overall yield, and to keep the developing tubers covered.
Tubers exposed to sunlight produce chlorophyll and turn green, indicating the presence of the bitter and potentially harmful compound solanine. To prevent this greening and maximize yield, hilling should begin when the potato plants reach a height of six to eight inches. At this point, loose soil, straw, or well-rotted compost is mounded up around the stems, covering all but the top one-third of the foliage.
This process is repeated two to three times throughout the early growing season, typically every two to three weeks, as the plants gain height. Each time, the added material increases the effective depth of the soil, providing a dark, cool environment for the tubers to enlarge. Loose garden soil is the traditional hilling material, but light materials like straw or compost are also good choices because they maintain a loose structure, making harvest easier. The final hilling should occur just before the plants flower or when the foliage naturally shades the ground, ensuring all potential tubers remain buried and protected from light.