Potatoes (Solanum tuberosum) are annual garden vegetables that complete their entire growth cycle, from the development of sprouts to the death of the parent plant, within a single growing season. During the season, this cycle progresses through five distinct stages.
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In the first stage of the cycle, new sprouts emerge from growth buds, or eyes, on the previous season's mature tubers. These sprouts are initially very pale, and they often appear as small white bumps on potatoes stored for a long time in the kitchen or pantry. When they emerge from a planted seed potato, the sprouts grow upward and eventually push above the surface of the soil. At the same time, new roots begin to grow from the potato's eye at the base of the sprout.
In the second stage of the cycle, the potato plant develops its above-ground structure, including stems, branches and leaves. The plant's root system also develops at this time, and the horizontal root shoots, called stolons, from which new tubers will grow begin to develop.
During the initial part of this vegetative growth stage, the plant gets nourishment from starch and sugars stored in the seed potato. Then, as leaves develop, the process of photosynthesis begins and the plant becomes capable of nourishing itself in preparation for new tuber growth.
In this stage, the tips of the stolons begin to swell, the first step in the development of new tubers, but the tubers do not yet grow substantially in size. This stage usually happens just before the plant flowers, but there is no direct connection between flowering and the beginning of tuber development.
In this stage, the plant directs most of it energy toward the growth of the new tubers. Water, sugars and nutrients begin to build up in the cells of the tubers. The cells swell, and the tubers increase dramatically in size.
In the final stage of the cycle, the plant's growth slows and eventually ceases entirely. Photosynthesis in the leaves slows down, and the tubers stop growing. Above ground, the plant turns yellow and starts to drop its leaves, and below ground, the skins of the tubers thicken in preparation for their dormant period. At the end of this stage, the plant dies.
During the maturation stage, sugars in the tubers are converted to starch, an efficient source of food for next year's plants, as well as an important component of high-quality potatoes for harvest.
Potato plants contain a toxic chemical called solanine. Solanine is present in all parts of the plant, but it is concentrated in new sprouts, unripe tubers and tubers that have turned green because of exposure to sunlight. Avoid eating any tubers or parts of tubers that appear green. Symptoms of solanine poisoning include vomiting and diarrhea.