How Potatoes Grow

Potatoes grow from other potatoes. A potato grows from a whole, small potato, or a piece of a larger one. The whole potato or cut piece has several recessed, dormant buds on its surface–these dormant buds are called “eyes”. When conditions are right, the buds will sprout and develop into independent plants.

Potatoes used to grow new potatoes are called seed potatoes. Seed potatoes are small tubers. A potato plant will also grow from a cut piece of a larger potato tuber as long as that piece has two or three dormant buds. A cut potato piece is called a “seed piece”. The small tuber or cut piece provides the new sprout or seedling with nourishment from its supply of stored starch.

There are five potato growth stages: sprout development, vegetative growth, tuber growth, tuber bulking, and maturation.

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Potato growth stages

When a seed potato or piece is planted, the potato growth stages begin. Here are the five potato growth stages

Stage 1: Sprout Development

After the seed potato or piece is planted, the piece provides nourishment for a sprout or seedling to grow. The eyes of the potato develop sprouts. The sprouts grow and emerge from the soil. Sprouts and stems rise from the ground two to six weeks after planting depending on the climate. A main stem and the first leaves begin to grow. The root system develops quickly and begins to absorb nutrients as the starch in the seed piece is used up.

Stage 2: Vegetative Growth and Photosynthesis

The leafy part of the plant puts on a lot of growth over a four or five weeks period. With proper sunlight, photosynthesis begins in the leaves and stems above ground. Excess energy is channeled downward as stolons (underground stems or “tubers”) develop. These tubers develop above the original seed piece, not below it. The tubers grow out from the entire length of the underground stem, starting at the bottom all the way to the uppermost section of the stem that is buried. The short underground stems (what we call potatoes) store nutrients. Soon, the main stem of the plant will stop growing and produce a flower bud.

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Potato plant flowering — When a potato plant flowers, that is a sign that the nutrient process and tuber development have begun underground. (

Stage 3: Tuber Growth

Tubers begin forming on the end of stolons; the stolon tips swell and tubers begin to form. Above ground, shoots develop ahead of flowers. Stolons usually swell before the plant flowers. (Because the “root” of the potato plant is a stem, not really a root, potatoes are considered tubers.) Tuber development begins 5 to 6 weeks after sprouts emerge from the soil. When a potato plant flowers, that is a sign that the nutrient process and tuber development have begun underground. (But, it’s important to note that some potato varieties produce potatoes with no flowering at all.)

Stage 4: Tuber Bulking

Tubers enlarge. Sugars and starches accumulate in the newly formed tubers. Optimal soil moisture and temperature as well as the availability of soil nutrients are very important during this time for the best yield. Tubers form best in cooler temperatures. The best crops are produced when the daytime temperature is in the 60° to 65°F range and when night temperatures are below 57°F. Fewer tubers form when temperatures are between 68° and 84°F, and no tubers form when temperatures are greater than 84°F. (When the weather is warm, the top part of the plant respires heavily, reducing the nutrients that can be put into storage in the tubers below ground.)

Stage 5: Maturation

As starch is stored in the tubers underground, the tubers enlarge and reach full size. The outside layer of the tuber gets tougher and tougher, keeping moisture within the potato. As the tuber skins harden, the leaves and stems above ground begin to dry out and die. Potatoes can remain underground for a while after the tops begin to die so that the last entry in the tops is transferred to the tubers. When the top of the plant dries out and yellows, tubers are ready for harvesting. The harvest of mature tubers can begin 10 to 26 or more weeks after planting (70 to 120 days) depending on the variety. However, potato tubers can be harvested at any size they are edible. If the skin of the harvested potato can not be rubbed off, it will store well.

Potato seed starting is further explained in Potato Seed Starting.

Potato growth of tubers — A potato plant lifted from the soil with developing and mature tubers.

Potato growth challenges

Keeping tubers buried is critical for their development. Sometimes new tubers may start growing at the surface of the soil. Exposed tubers should be buried ahead of harvest. Exposure to light leads to an undesirable greening of the skin and the development of solanine as protection from the sun’s rays, growers cover surface tubers. Solanine is an alkaloid found in potatoes and other Solanaceae family plants. If ingested, solanine can cause poisoning in humans and animals. “Hilling up” or “earthing up”—the piling of additional soil around the base of the plant as it grows—inhibits the development of solanine. An alternative to “earthing up” is covering plants with straw or other mulches.

Home gardeners often grow potatoes from a piece of potato with two or three eyes, commonly in a hill of mounded soil or in a grow bag or containers. Commercial growers plant potatoes as a row crop.

Potatoes are sensitive to heavy frosts, which damage them in the ground. Even cold weather makes potatoes more susceptible to bruising and possibly later rotting.

Potato plant planting and growth are further explained in How to Plant, Grow, and Harvest Potatoes.

Commercial seed potatoes are specifically grown to be free from disease and to provide consistent and healthy plants. Commercial seed potato growing regions usually have cold winters that kill pests and summers with long hours of sunlight each day for optimum growth.

Potato growing quick tips

Planting: In cold winter regions, plant seed potatoes in spring as soon as the soil can be worked. For a summer crop where the soil temperature does not climb above 85°F (20°C), plant 2-3 weeks before the last frost. For a fall crop, plant in late spring. In mild-winter regions, plant in late winter—4 to 6 weeks before the last frost—for a summer crop. Plant in late summer for a winter-into-spring crop. Potatoes are tolerant of cool soil and late frost. Set seed potatoes 2 to 4 inches (5-10 cm) deep and 12 to 18 inches (30-45 cm) apart in all directions. Plant seed potatoes in soil rich in compost and rotted manure.

Growing: When plants are 12 inches (30 cm) tall, draw the soil up around them—called “hilling”—so just a few inches (5 cm) of the plant is seen. Hilling will protect potatoes from sunburn and from turning green. Grow potatoes in full sun. Keep the soil just moist. Add a side-dressing of high phosphorus fertilizer to the soil after 1 month of growth.

Harvesting: Potatoes planted in early spring will be ready for harvest in 90-110 days; planted in late spring, 100-120 days; planted in late summer or fall, 110-140 days. Dig early for “new potatoes” when plants begin to bloom and fade; dig for mature, full-size potatoes when the vines are yellow and die. To harden the potato skin before harvest, stop watering 2 weeks before harvest; cut away the top foliage 10 days before harvest. Carefully lift potatoes with a garden fork, starting 8 to 10 inches (20-25 cm) away from the plant, then work closer t the vine. Brush but do not wash clinging soil from tubers. Store potatoes in a dry, dark, well-ventilated place for up to 6 months.

For more detailed articles on potatoes click on Potatoes.