Potatoes Solanum tuberosum

Potatoes are herbaceous perennials in the nightshade family (Solanaceae), but they are grown as annual crops. Potatoes are native to South America in parts of Argentina, Bolivia, Chile and Peru. They are now widely cultivated and major producers include China, Germany, India, Russia and the United States. The genus name, Solanum, is derived from the Latin word, solamen, which means "comforting or soothing." The species name, tuberosum, means "tuber."

Potatoes grow best in full sun and well-drained, sandy and acidic soil. Poorly drained soil may cause tubers to rot, and acidic soil helps to prevent bacterial scabs. Light soil, if consistently moist, can help the plant grow large, evenly shaped potatoes. Raised beds provide good drainage and containers or grow bags can be suitable for growth as long as they are at least 2 feet deep and hold at least 30 gallons. Potatoes also may be grown in trenches to make the process of hilling easier. 

Potatoes are most often grown from "seed potatoes," which are small tubers or pieces of tubers that sprout into a new plant. Buying certified disease-free seeds can help prevent problems such as potato late blight. Potatoes from the grocery store are often treated with sprout inhibitors and therefore may not be reliable for planting. Before planting, cut seed potatoes so each piece has at least two eyes and allow it to rest outside for a day to let the cut end scab over. Plant seed pieces 5 to 6 inches apart with the eyes facing up. As they grow, pile soil or mulch up around the base of the plant. This encourages the growth of more tubers along with the submerged parts of the stem. Do this once the plants are one foot tall and once or twice more throughout the season. Tubers will turn green and produce toxic compounds if not sufficiently covered. In North Carolina try to have potatoes planted sometime between mid-February and the end of March; they can tolerate a bit of frost. 

Potatoes can be harvested mature when the tubers are fully grown or the plant has dried up around June. They may also be harvested early as "new" potatoes once the plants begin to flower. These young potatoes still have thin, delicate skins and are considered a delicacy. New potatoes can be harvested about 7 to 8 weeks after planting. Mature potatoes can take 3 to 4 months before they are ready for harvest. Proper crop rotation, clean garden tools and using disease-resistant cultivars will reduce pests and diseases which ultimately improves crop yields. 

The plant produces stolon's that bear edible underground tubers. All green parts of the potato plant are inedible because they contain a toxin known as solanine. This toxin can be found in the sprouts, stems, leaves, berries, and the green skin of the tuber. Potatoes are cultivated for their starchy tubers and are the fourth most important food crop. Thousands of cultivars exist in varying textures, sizes, and colors that are suited for a variety of culinary uses. Russet potatoes are most commonly found in stores and restaurants. They are better suited for the climate of the western United States and do not grow well in the eastern states. For North Carolina's climate and soil, some of the most reliable cultivars include thinner skinned potatoes such as ‘Yukon Gold’, ‘Kennebec’ and ‘Red Pontiac’.

Quick ID Hints:

• Underground edible tubers.
• Above-ground plant has green erect, branching, smooth to sparsely hairy stems.
• Leaves dark green, pinnately compound, with six to eight leaflets, sparsely to densely hairy.
• Flowers white, pink, purple, or blue with yellow stamens.
• Green or yellowish-green berries about one-half inch in diameter sometimes appear.

Insects, Diseases and Other Plant Problems:  Potatoes are susceptible to the Colorado potato beetles, flea beetles, wireworms and leafhoppers. Colorado potato beetles lay masses of yellow eggs and the larvae defoliate plants. Potato late blight will rot tubers and render them inedible. Viral, bacterial, and fungal diseases are potential problems. If this occurs, it is best to remove and destroy the diseased plants.

The Clemson Cooperative Extension Home and Garden Information Center has a factsheet on common irish potato insect pests.

VIDEO Created by Elisabeth Meyer for "Vegetables, Herbs, Fruits, and Nuts" a plant identification course offered in partnership with Longwood Gardens.