What Are Seed Potatoes?

The potato plant (Solanum tuberosum) is a herbaceous perennial that is widely grown in U.S. Department of Agriculture plant hardiness zones 2 to 11. It is, however, not frost-tolerant and is grown as an annual in areas where temperatures fall below freezing. Most gardeners dig up the entire plant at the end of the growing season and start new plants from seed potatoes the next season.

The potato plant grows from underground tubers and reaches a height of about 18 inches. As the plant grows, additional edible tubers will form in the root system at the base of the plant. Gardeners mound soil around the plant's base to encourage the development of tubers and to protect the tubers from exposure to light.

New potato plants are not grown from seed but rather from whole tubers or sections of tubers called seed potatoes. To grow a new plant, each one of these seed potatoes must contain at least one bud, called an eye, from which a new stem will sprout.

Potato plants are quite prolific, and seed potatoes can provide a significant return on investment in terms of the number of new tubers produced by each seed potato. In good growing conditions, 2 pounds of seed potatoes may produce as much as 50 pounds of new potatoes.

Potatoes bought from the supermarket, when left in a cool, dark place, may sprout from their eyes, but you should resist the temptation to use these tubers as seed potatoes in your garden. Supermarket potatoes are often treated with sprout-inhibiting chemicals which can hinder their growth, and they may also harbor disease.

Instead, buy seed potatoes from a local garden or seed supplier, or through online or mail-order sources. Buy seed potatoes that are certified to be free from diseases such as the Fusarium fungus, and don't plant any seed potatoes that show signs of disease.

To prepare seed potatoes for planting, cut the potatoes into pieces about an inch wide; potatoes less than about 2 inches wide may be planted whole. Each seed potato must contain at least one eye, and at least two eyes are preferable.

Cut potatoes will only heal if they're exposed to cool temperatures, high humidity and oxygen for a period of several days after they're cut. Because those conditions are unlikely to be met if the seed pieces are immediately planted, they should be cured for at least several days to reduce the chance that they'll rot in the ground.

To cure seed potatoes, put them in a paper bag and store them at room temperature for two to three days. After that time has passed, shake the bag to separate those cut potatoes that adhered to one another, and then store them for another two or three days before planting. If you keep the potatoes in the bag until they begin to sprout, the new shoots will emerge more quickly once they're planted, which may be helpful if you're planting late in the spring.