Hilling is an agricultural practice that involves progressively mounding soil or other material around the base of a growing potato plant. This technique directly increases the final harvest yield by burying the lower part of the main stem. This encourages the plant to produce more specialized structures where the edible tubers form. This article explores the biological mechanisms, the safety function hilling provides, and practical instructions for implementing the technique.
How Hilling Increases Potato Production
The potato tuber is a modified underground stem, not a root vegetable. These storage organs develop on specialized horizontal stems called stolons, which grow from the nodes of the main stem beneath the soil surface. A potato plant naturally produces a limited number of stolons from the initial nodes near the planted seed piece.
When the lower part of the main stem is covered with soil through hilling, the buried portion is stimulated to produce additional stolons. Each new stolon represents a potential site for a tuber to develop. Repeated hilling throughout the growing season provides a continuous opportunity for the plant to form more tuber-bearing structures. This direct stimulation of stolon and tuber formation is the primary way hilling contributes to a larger overall harvest by increasing the quantity of potatoes per plant.
Protecting Tubers from Light and Solanine
While increasing yield is a major benefit, hilling also maintains the quality and safety of the developing tubers. Potatoes are sensitive to light exposure. If a tuber grows too close to the soil surface or becomes uncovered, it begins a process called greening, caused by the production of chlorophyll.
The light exposure that triggers chlorophyll production also stimulates the biosynthesis of toxic compounds known as glycoalkaloids, primarily solanine and chaconine. Solanine acts as a natural defense mechanism, making the exposed tuber bitter and potentially harmful if consumed. Although the green color itself is harmless, its presence indicates that the levels of these glycoalkaloids have increased. Hilling ensures that the developing tubers remain buried under a sufficient layer of soil, preventing light from reaching them and inhibiting the formation of solanine, thus preserving the edibility of the crop.
Practical Guide to Hilling Techniques
The hilling process should begin when the potato plants have reached a height of about six to eight inches above the ground. At this stage, material is pulled up around the plant’s base until only the top few inches of leaves remain exposed. Care should be taken not to bury the actively growing terminal leaves, as this can impede growth.
The process is typically repeated two or three times during the early to mid-growing season as the plants continue to grow in height. The second hilling usually occurs two to three weeks after the first, or just before the plants begin to flower. This progressive mounding should create a final ridge that is approximately 10 to 12 inches high.
While garden soil is the traditional material, other organic materials are often used for hilling, including straw, compost, or aged mulch. Straw is a popular alternative because it is lighter, which makes harvesting significantly easier. However, it may require a thicker layer to block light as effectively as dense soil. Regardless of the material chosen, the goal remains to continually cover the emerging stem and maintain an opaque barrier over the developing tubers.