Each spring, gardeners decide what potatoes they will grow and prepare seed potatoes for planting. Depending on the varieties, the time from planting to harvest can take 80 to 150 days. Tuber growth success starts with the manner in which seed potatoes are prepared. Equally vital are air and soil temperatures, light and length of days, soil composition, moisture and nutrients. It's also essential to manage pests. Each factor influences the five stages of development in the potato plant.
The first phase of development is often seen in the kitchen when potatoes have been around too long and begin to sprout. The University of Florida Extension, however, discourages planting potatoes from the grocery store because of potential disease and treatment with sprout inhibitors. When preparing seed potatoes, gardeners cut chunks, each of which has at least one eye. After these pieces are planted, a sprout emerges from the eye and start growing toward the surface. This takes 10 to 14 days. Gardeners must protect newly emerged sprouts by covering them with soil. At this stage, the potato is supplying the energy needed to promote development.
Within 30 to 70 days, roots and underground stems, known as stolons, begin to develop, and branches and leaves emerge from the soil. Potato plants can have several main stems. It is also during this stage that plants need to be side dressed with 3/4 lbs. of nitrogen and 1/2 lb. of potassium per 100-foot row. Do this three to four weeks after planting. Spread fertilizer four to six inches on either side of the plant and cover the fertilizer with two inches of soil. This is when photosynthesis begins. During photosynthesis, the plant absorbs energy from the sun's rays and converts that energy into food for growth. The sun's energy is initially stored as sugar. The plant combines these sugars with carbon dioxide and water and converts this mixture into carbohydrates, which fuel tuber formation.
Formation of Tubers
During the next two weeks, new potatoes begin to form on the tips of the stolons beneath the surface, but they will not grow. Toward the end of this stage, early flowering begins. Cool night temperatures and a moderate amount of nitrogen enhance tuber development. The nitrogen and potassium added to the plant in the previous phase is enough to form tubers. Plants lacking sufficient water will begin this phase earlier than those receiving plenty of water.
Growth of Tubers
In this phase, the plant goes from putting energy into vine expansion to tuber enlargement. Water, nutrients and carbohydrates contribute to this growth. The number of tubers that fully mature directly correlates with the provision of these elements. During this bulking process, potatoes must be kept covered with soil to avoid toxicity. Malformation of tubers may occur because of temperature changes and a lack of nitrogen and water. These factors, along with plant spacing and inadequate pest and disease management, can affect yield and potato size. This critical growth stage can take three months.
As photosynthesis decreases, potato vines yellow and eventually die. As this happens, skins of the mature potatoes harden and thicken. Additionally, sugars convert to starch and dry matter increases. Plants from long season varieties of potatoes grown in areas with short seasons may not go through the die back process.