The five distinct stages of development for a potato include sprout development, vegetative growth, tuber initiation, tuber bulking, and maturation. Environmental factors such as temperature, sunlight, moisture, nutrients and soil conditions influence the growth, and quality of the potato. Many factors are uncontrollable by the grower (air and soil temperature, humidity and wind); however, growers control other factors to increase yields, such as the variety of potato, stem population, moisture and nutrients.
During stage one the eyes (small black spots on the seed potato skin) break dormancy and develop sprouts. This stage continues until the sprouts emerge from the soil. During this stage, the seed tuber is the only energy source for the plants' growth.
The vegetative growth stage is when all parts of the plant form. After the sprouts break through the soil, branches, leaves, roots and stolons (stems bearing roots that run horizontally) soon emerge. Normally, the stored soil moisture from spring rains or pre-plant irrigation is sufficient for growth; however, monitoring moisture levels is critical since the majority of the root mass lies within the top 18 to 24 inches of the plant profile. The first two growth stages last from 30 to 70 days, depending upon planting date, temperature, soil conditions, and cultivar selection
Tuber initiation begins when the ends of the stolons swell and tubers start to develop but do not enlarge. The number of tubers formed per plant is called a tuber set. Lack of moisture decreases the formation of tubers consequently reducing the overall yield. The initiation stage of the potato plant lasts approximately two weeks.
Water, nutrients and carbohydrates cause the tuber cells to expand, increasing the tubers size and weight. Only about 5 to 15 of the initial tubers grow, while the rest are used for nutrition or absorbed by other potatoes. Varying environmental conditions, such as fluctuating temperatures, lack of moisture or nutrients in the soil, cause uneven growth, cracks or abnormalities in the tuber shape. The longest of the growth stages, tuber bulking lasts up to three months depending on the planting date and choice of cultivar.
Tubers are mature when the plant canopy (the vines, leaves and braches) starts to die. During this stage, photosynthesis decreases, and the tuber growth slows. Some growers help the dying process. When growing a long season variety in a short season locale, such as the Russet Burbank (common baking potato), growers spray the plant canopy with herbicide to kill the plant prior to harvesting the tubers. Other varieties mature naturally, and harvesting commences when there is nothing left of the plant canopy but decayed stems and leaves; however, growers harvest red potatoes early to maintain the preferred smaller size.