Potatoes are unique because the edible portion, the tuber, does not grow from the plant’s root system. Instead, tubers form on specialized stems called stolons, which develop only along the underground part of the main plant stem. The depth and volume of the surrounding soil directly dictate the available space for tuber formation and the final harvest yield. Managing the growing medium is the most important factor in potato cultivation, as the plant must be continuously encouraged to develop more stem below the surface. This dependency explains why the total soil volume required for potatoes is significantly greater than the initial planting depth.
Initial Planting Requirements
Planting the seed potatoes at a specific, relatively shallow depth is necessary. Seed pieces should be placed three to five inches below the soil surface in a prepared trench or bed. This initial coverage is necessary to shield the seed from light and provide a stable base for the plant’s root system to anchor itself.
Proper spacing between plants is also important for allowing the tubers sufficient room to expand underground. Place each seed potato about 10 to 12 inches apart within the row. The rows themselves should be spaced between 30 and 36 inches apart, to ensure adequate access for later cultivation and the subsequent process of mounding soil around the growing plants.
The Critical Role of Hilling
Hilling is the practice of gradually adding loose soil, compost, or straw around the base of the potato plant as it grows. This is a repetitive process that progressively increases the depth of the growing medium throughout the early season. The primary function of hilling is to bury the lower portion of the developing stem, which stimulates the plant to produce more tuber-forming stolons along the covered section. The more stem that is buried, the more potential sites are created for new potatoes to form, directly increasing the plant’s overall yield.
The timing for the first hilling is when the emerging green shoots reach a height of about six to eight inches above the ground. At this point, the growing medium is brought up around the stems until only the top few inches of foliage remain exposed. This process is repeated one or two more times as the plant grows, typically every few weeks, until a final soil mound is created. The total height of this finished hill should aim for six to eight inches of added material above the initial ground level, resulting in a total coverage depth of roughly 10 to 12 inches above the original seed potato placement.
Hilling serves a second important biological purpose: preventing light exposure to the developing tubers. Potato tubers that are exposed to sunlight will begin to photosynthesize, turning green due to chlorophyll production. Along with chlorophyll, the potato synthesizes glycoalkaloids, primarily solanine. Solanine is a toxic compound, so maintaining a thick layer of soil to block all light is a necessary safety measure for producing edible potatoes.
Minimum Soil Volume for Container Growing
When potatoes are grown in containers, the total required soil volume must allow for the same deep coverage achieved with hilling in the ground. The container must provide sufficient vertical depth to accommodate both the initial planting and the subsequent mounding of the growing medium. A minimum depth of 14 to 15 inches is required for any container, such as a large bucket or grow bag, to successfully grow a potato plant to maturity.
In volumetric terms, a single potato plant requires a minimum of five gallons of soil volume to produce a reasonable yield. For practical container sizing, this translates to a container with a capacity of at least 10 gallons, which can accommodate two potato plants. The container’s diameter is also important, as it needs to be wide enough to allow the developing tubers to spread out, requiring a container that is at least 14 inches wide at the bottom.
The principle of hilling remains the same in a container. The seed potato is initially planted shallowly in four to six inches of soil at the bottom. As the plant grows, soil is continually added until the container is nearly full, providing the necessary vertical space for stolon development.