Potatoes are a staple food, but when they sit on the counter or in the pantry for a while, they often begin to develop small growths. The simple explanation is that the potato itself is not a root but a living, swollen stem called a tuber. This tuber stores energy for the plant’s next growth cycle. The appearance of roots and sprouts is the potato attempting to fulfill its biological purpose. This growth, sometimes called “chitting,” is a natural process that indicates the tuber’s dormant phase has ended.
Understanding Dormancy and Biological Triggers
After a potato is harvested, it enters a resting period known as dormancy, where its growth is temporarily suspended. This state ensures the tuber does not sprout underground before conditions are favorable. The surface of the potato contains small indentations known as “eyes,” which are nodes where new stems and roots will initiate growth.
Dormancy is eventually broken by environmental cues, signaling that it is time to regenerate. The three primary factors that trigger this growth are warmth, light, and moisture. Higher temperatures, especially those around 70°F (21°C), accelerate the potato’s metabolism and encourage the development of sprouts.
Root growth, distinct from the white or purple sprouts, is specifically triggered by excess moisture or high humidity. When the potato senses a damp environment, it initiates root development to establish itself and draw water. Therefore, seeing roots often means the potato has been stored in a place that is too wet or humid.
Determining When Rooting Affects Edibility
The primary concern with a sprouting or rooting potato is the potential increase in naturally occurring compounds called glycoalkaloids, primarily solanine and chaconine. These compounds function as a natural defense mechanism against pests and disease, and their concentration rises significantly when the potato is stressed, greening, or sprouting.
Solanine is concentrated in the sprouts, the eyes, and any green areas on the skin. Consumption of high levels of glycoalkaloids can lead to mild toxicity, causing symptoms like nausea, vomiting, abdominal pain, and diarrhea. Importantly, cooking methods like boiling or frying do not effectively eliminate these toxic compounds.
If the potato has only minimal sprouting or rooting, it is generally safe to consume, provided you generously cut away and discard the sprouts and any green areas. However, if the potato is soft, shriveled, extensively sprouted, or has a noticeable greenish tint, its glycoalkaloid content is likely too high. In these cases, it is safest to discard the entire potato to avoid illness.
Optimal Conditions for Storage and Prevention
Preventing root and sprout growth involves managing the three environmental factors that break dormancy. The ideal storage location for potatoes is a cool, dark, and well-ventilated space.
Temperature is the most significant factor, with the ideal range for inhibiting growth being between 42°F and 50°F (5.5°C and 10°C). Room temperature is too warm and will accelerate sprouting. Temperatures below 40°F (4.5°C), such as in a refrigerator, cause the starch to convert to sugar, resulting in an undesirably sweet flavor and dark color when cooked.
Light must be excluded entirely to prevent greening, which signals the accumulation of solanine just beneath the skin. To specifically prevent root growth, ventilation is necessary to reduce excessive surface moisture and high humidity. Potatoes should be stored loosely in a paper bag, basket, or open container, not sealed in a plastic bag, to allow for air circulation and prevent dampness.