Potatoes are one of the most widely grown garden vegetables. Successful cultivation begins with understanding the planting material: the “eyes” are vegetative buds from which new plants sprout. A “seed potato” is a potato, or a piece of one, used for planting, providing food reserves for the emerging sprout. Correct initial planting depth is a foundational step in managing how potatoes develop their edible tubers.
Preparing the Seed Potatoes for Planting
Select certified disease-free seed potatoes. Large tubers should be cut into blocky pieces, weighing approximately 1.5 to 2.5 ounces (about the size of a chicken egg). Each resulting piece must contain at least one or two distinct eyes to ensure a viable sprout develops.
After cutting, the seed pieces must be allowed to “cure” for one to seven days before being placed in the soil. Curing involves letting the cut surfaces dry out and form a protective, leathery callous. This process prevents the seed piece from rotting prematurely, which is a common problem when planting in cool, moist soil. Allowing the wound to heal reduces the entry points for soil-borne diseases and fungal pathogens.
Initial Planting Depth and Soil Temperature
The recommended initial planting depth is between three and five inches below the soil surface. This depth provides a stable, moist environment for the seed piece to sprout and gives the emerging stem initial cover. In heavy or clay-rich soil, a shallower depth of two to three inches is preferred to prevent saturation. Conversely, in lighter, sandy soils, planting closer to five inches deep helps retain moisture.
Soil temperature is more important than precise depth and should be at least 45°F for planting. Planting in colder soil increases the risk of the seed piece rotting before sprouting. Optimal soil temperatures for robust tuber development range between 61°F and 66°F. Since tuber formation is inhibited above 80°F, early planting in cool soil is a beneficial strategy for long-term success.
Why Hilling is Necessary
Hilling, or mounding soil around the base of the plant, is necessary to maximize yield. Potato tubers form along the underground portion of the stem, not from the seed potato itself. By continually burying the lower stem, the gardener encourages the plant to produce more tuber-forming structures, called stolons, resulting in a larger harvest.
The second purpose of hilling is to prevent developing tubers from being exposed to sunlight. Light exposure causes the tubers to photosynthesize and turn green due to chlorophyll production. This greening correlates with the development of solanine, a toxic glycoalkaloid.
Hilling should begin when potato plants are six to eight inches tall, covering the lower two-thirds of the stem with loose soil or organic mulch. This process must be repeated several times throughout the growing season as the plant grows upward. The goal is to keep the developing potatoes completely covered to shield them from light and maintain a cool, dark environment.
Optimal Spacing Requirements
Horizontal spacing between plants significantly impacts the size and quantity of the final harvest. Seed potato pieces should be spaced 10 to 15 inches apart within the row. Closer spacing (8 to 10 inches) encourages a higher number of smaller tubers, ideal for harvesting new or baby potatoes.
To produce fewer but larger potatoes for long-term storage, space the seed pieces 15 to 20 inches apart. Adjacent rows should be spaced 24 to 36 inches apart (two to three feet). This wider row spacing allows ample room for hilling and ensures good air circulation, reducing the risk of foliage diseases.