The potato is a staple food crop globally, valued for its dense carbohydrate content and adaptability to various climates. Although often mistaken for a root, the edible portion is physiologically an underground stem known as a tuber, which stores energy for the plant. The life cycle of the potato plant, Solanum tuberosum, unfolds through five distinct physiological stages, governing the plant’s growth and the eventual quality of the harvest.
Sprouting and Plant Emergence
The growth cycle begins with a “seed potato” or “seed piece,” which contains small indentations known as “eyes.” Each eye is a node capable of developing into a shoot. To initiate growth, the seed potato must be placed in soil with sufficient moisture and warmth, typically above 45°F (7°C), to break dormancy.
Sprouts grow upward, utilizing the stored energy within the seed piece to fuel initial development. This subterranean phase continues until the shoot pushes through the soil surface. The appearance of the first true leaves above ground marks the completion of emergence and the plant’s transition to vegetative growth.
Canopy Development and Stolon Growth
Following emergence, the plant enters a period of rapid vegetative expansion, developing a dense foliar canopy above ground. The primary function of this canopy is photosynthesis, harnessing sunlight to produce carbohydrates that will later be deposited into the tubers. Simultaneously, specialized lateral stems called stolons begin to grow horizontally underground from the base of the main stem.
These modified stems are the sites where new tubers will form. Growers often practice “hilling,” mounding soil up around the base of the plant. Hilling serves two purposes: it encourages the development of more stolons, potentially increasing the number of tubers, and it shields the developing stolons from light exposure. Light exposure would otherwise cause the tubers to turn green and produce the toxic compound solanine.
Tuber Development and Bulking
The most significant physiological shift from vegetative to reproductive growth is known as tuber initiation. At this stage, the tips of the underground stolons begin to swell as the plant alters its energy allocation. Carbohydrates produced by the canopy are no longer primarily used for stem and leaf growth but are translocated and stored in the developing tubers.
Initiation is quickly followed by “bulking,” a prolonged period lasting 45 to 60 days where the tubers rapidly increase in size and weight. The developing tubers accumulate water, starches, and mobile nutrients like potassium and nitrogen. A consistent supply of water and nutrients during this phase is important, as the rate and duration of bulking directly dictate the final yield and size distribution of the harvest. High temperatures, particularly above 86°F (30°C), can inhibit this process, reducing starch storage and slowing the bulking rate.
Final Maturation and Senescence
The final stage is marked by senescence, the natural decline and dying back of the plant’s foliage. The green leaves begin to yellow and brown as the plant stops producing new carbohydrates and remaining resources are mobilized into the tubers. Even though the plant is no longer actively growing, this stage is important for preparing the tubers for storage.
The tuber skin, which was thin and easily damaged during the bulking phase, begins to thicken and harden in a process known as skin set. This physiological change provides a protective layer, reducing water loss and susceptibility to disease after harvest. After the foliage dies back, the tubers are typically left in the soil briefly to complete skin set before being lifted. Post-harvest, a short period of “curing” in a cool, humid environment allows minor harvest wounds to heal, further preparing the potatoes for long-term storage.