History

White or Irish potatoes originated in the Peruvian Andes. These primitive potatoes were peanut to plum size. Incas used them to make chuño, an early sort of instant potatoes. To prepare chuño, potatoes were frozen, thawed, repeatedly stomped on to form a dark dried mass, then rehydrated before use.

Spanish conquistadores introduced potatoes to Spain in the 1500's and potato usage spread from Spain to Italy and France. Potato cuisine nearly failed in the court of England's Queen Elizabeth I. The queen's cooks prepared the tops instead of the tubers, making the diners deathly ill due to solanine and chaconine, two poisonous alkaloids found in high concentrations in the foliage.

Ireland was more receptive to the humble tuber. Due to ideal weather and soil, potatoes had become an important crop in Ireland by the late 1700's. Tenant farmers raised high value grain to pay their rent and grew low value potatoes to feed themselves. They became dependent on potatoes for sustenance. In 1845-46 a fungal disease caused by Phytophthora infestans ravaged the Irish potato crop resulting in the Irish Potato Famine. Anywhere from one to two and one half million Irish died during the famine (out of a population of nine million) and an estimated one and one half million Irish emigrated.

Culture

Potatoes come in many colors, ranging from the common red or tan skin to blue or yellow. Regardless of skin color, most have white flesh, though there are some yellow or blue-fleshed potatoes.

Potatoes can be ready to harvest anywhere from about 65 days from planting for the earliest varieties, to over 90 for the late season varieties.

Site selection

Plant potatoes as early in spring as the garden soil can be tilled easily. Soil should be so dry that a soil ball will crumble if poked slightly. If frost threatens newly emerged plants, simply cover them with soil. They will grow up through the soil.

Use certified disease-free seed potatoes. If possible, sow potatoes in a site where potatoes, eggplant, tomatoes or peppers have not been planted for several years. This rotation prevents buildup of disease organisms in the soil.

Loamy soil high in organic matter works best for growing potatoes. If you have heavy clay soil, incorporate compost or peat moss to loosen it.

Potatoes grow best in soils with a pH range between 6.0 and 6.5. However, they will grow in soils with pH levels as low as 4.8 to 5.4--the pH range commercial growers strive for as scab is less likely to occur in such acidic soil. (If scab occurs, just peel it off as it's usually a cosmetic problem, unless tubers are severely infected.)

Planting

Cut seed potatoes into pieces about the size of an ice cube with at least one eye or bud per piece. (Small potatoes may be planted whole.)

If you're planting potatoes when the ground is still somewhat cool and damp, dust cut potatoes in sulfur right after cutting them. To do this, put the cut potatoes into a plastic bag together with sulfur, then shake them until they're coated. One ounce of sulfur is enough to treat ten pounds of potatoes.

Cut seed potatoes, whether sulfur treated or not, should be "cured" before they're planted in order to reduce rot. To cure them, spread potatoes out in a warm, humid place at 70°F. Let them sit for two days so cut surfaces dry.

To plant, dig a trench six inches wide and eight inches deep. Place seed pieces cut side down ten to twelve inches apart. Rows should be three feet apart. Potatoes planted closer together will produce smaller tubers. Wider spacing produces fewer but larger tubers. Cover potatoes with four inches of soil.

Care

Hilling or piling soil up along the stems causes the stems to lengthen. Potato tubers form on runners that emerge from the plant stem, so the longer the stem, the more runners the plant will form, creating more potatoes. Start hilling your potatoes as soon as shoots appear, about two weeks after planting. Hill them again two or three times later, filling in the trench as you go. Always leave four inches of stems and leaves uncovered.

Fertilize with 5-10-10 at a rate of one and one half pounds per 100 sq. ft. of garden space or one pound per 25 feet of trench. You can also apply fertilizer in a band six inches from the plants before hilling them.

Harvest

Tubers start to develop six to ten weeks after planting. Harvest new potatoes mid-summer, about eight weeks after planting. You can carefully remove one small new potato per plant without reducing overall yield. If you want to harvest more, you may be better off harvesting an entire plant or two.

Be sure the tubers are covered with soil at all times. Light triggers production of chlorophyl which occurs concurrently with the production of solanine and chaconine in potato tubers. In small quantities these alkaloids contribute to the potato flavor, but in higher concentrations they impart an unpleasant, bitter taste. The alkaloid solanine can make you ill if you eat too much of it. Peel off all green portions when preparing potatoes for a meal. Be sure to store raw potatoes in a dark place.

Harvest potatoes for overwinter storage after their tops have died. Storage potatoes have thicker skin than new potatoes that were dug before the tops died. If you rub your thumb on a potato and the skin sloughs off easily, it is not ready for storage. Potatoes with thick skins store best.

Use a spading fork to dig the hills. Leave potatoes outside in a shady spot for a few hours to dry. Don't wash them. As soon as the surfaces have dried, store the potatoes for a week or two in a dark area with temperature of 55° to 60°F and high relative humidity. This storage will "cure" the potatoes and seal any harvest injury.

Storage

Once potatoes have been cured, move them into winter storage. Choose a dark location with moderate to high humidity, good air circulation and temperatures between 40° and 55°F. Store the tubers no more than six to eight inches deep. Mature tubers should keep up to eight months when stored at 40°F. They'll sprout sooner at warmer temperatures.

If potatoes are stored at temperatures near freezing, the starch converts to sugar and potatoes will have an unusually sweet flavor. If this happens, move the potatoes to a room with temperatures in the 55° to 65°F range, and the normal flavor should return in a day or two.

Store potatoes away from apples and pears as these fruits release ethylene which hastens sprouting. Potatoes may rot more quickly when stored with onions, but that is because onions store well at warmer temperatures than potatoes. Potato tubers stored at temperatures warmer than 55°F will shrivel and the eyes will sprout. Discard these potatoes.

H212P
Reviewed 10/98