Growing potatoes successfully relies less on a single perfect planting depth and more on a continuous process of soil management. A “seed potato” is not a true seed but a small tuber or a piece of a larger potato containing at least one eye, the bud from which a new plant will grow. These seed pieces must be covered with soil at all times because the edible potatoes (tubers) develop along the buried portion of the stem. Maintaining sufficient soil coverage is necessary to prevent the tubers from being exposed to light, which would compromise their quality and safety.
Determining the Initial Planting Depth
The initial planting depth for seed potatoes is intentionally shallower than the final depth the plant will ultimately occupy. For traditional row planting, a trench is typically dug 6 to 8 inches deep, and seed potato pieces are placed inside, covered with only 3 to 4 inches of soil. This shallower covering allows the soil around the seed piece to warm up faster, promoting quicker emergence of the sprouts above the ground. Planting the seed piece in a prepared trench sets the stage for future growth and the technique of adding more soil later.
The Essential Practice of Hilling
Hilling, also known as earthing up, is the most important depth-related practice in potato cultivation. This technique involves continually mounding loose soil, compost, or straw around the base of the stems as they grow, starting once the green shoots reach 6 to 8 inches. The two main purposes of hilling are to encourage higher yields and to protect the developing tubers. Burying the lower stem stimulates the production of more roots and stolons, the underground stems where new tubers form, which lengthens the productive area and increases yield. Hilling also shields against light exposure; if tubers are exposed to sunlight, they turn green due to solanine, a natural toxin that makes them unsafe for consumption. The mounding process is repeated every two to three weeks, covering about two-thirds of the visible stem each time until the foliage is fully developed.
Depth Considerations for Container Growing
Growing potatoes in containers, such as grow bags, barrels, or large pots, requires a modified approach to managing planting depth. A container should be at least 10 to 15 gallons in capacity and 2 to 3 feet deep to provide adequate vertical space for tuber development. The seed potato is initially placed near the bottom, covered with only 4 to 6 inches of soil or potting mix. As the plant sprouts and the stems grow, the process of hilling is integrated by gradually filling the container with more soil. Instead of pulling soil from between rows, the grower adds new material, burying the stem until only a few inches of foliage remain exposed.
What Happens When Depth Is Incorrect
Incorrect planting depth significantly impacts the health and yield of the potato crop. Planting the seed potato too shallowly increases the likelihood that developing tubers will be exposed to sunlight. This exposure triggers the production of solanine, turning the potatoes green and rendering them inedible. Shallow planting also leaves the young plants more vulnerable to late spring frosts and rapid soil drying. Conversely, planting the seed potato too deeply can delay the emergence of the sprouts; the seed piece may rot in cold, wet soil, or the resulting plant will emerge later, reducing the overall growing season and diminishing yield.