Potatoes

Potatoes tend to require more care and attention than most other vegetables. The potato has specific soil requirements and thorough insect and disease control is necessary for potato crops. A good yield is 150 to 175 pounds of usable potatoes from 100 feet of row.

Seed Selection

Use only certified disease-free “seed” since it is grown under rigid rules and carefully inspected by state authorities. However, potato “seed” is not a true seed but rather a modified stem known as a tuber. (The true seed of the potato occurs in the small, inedible orange fruit the plant produces during mid-season.) Some feed and garden stores  sell B-size seed-small tubers weighing 1½ to 2 ounces. These tubers should not be cut before planting. If 4 to 6 ounce or larger tubers are used cut them so that each piece is block shaped, contains at least one good eye or bud and weighs about 1½ ounces. Plant immediately after cutting.

Soil Requirements, Seedbed Preparation, and Planting

A well drained, fine sandy loam that is high in organic matter is preferred. If a  cover crop (rye or wheat are excellent choices) was planted the previous fall it should be turned under before it exceeds 12 inches in height by tilling 8–10 inches deep, depending on the depth of the topsoil. After tilling, level the surface slightly so furrows can be made. It is best to wait at least a week after tilling in the cover crop before planting the seed pieces.

Plant the seed in shallow trenches 3½–4½ inches deep and cover with 1–2 inches of soil. The seed pieces should be spaced 9–12 inches apart in rows 28–34 inches apart. From 9–12 pounds of seed will be needed for each 100 feet of row when 1½–2-ounce seed pieces are planted 12 inches apart.

Soil pH and Fertilizer Practices

Because scab disease (brown corky tissue on surface of tubers) may be a problem  in alkaline or "sweet" soils, the pH should be 5.0 to 5.5. Liberal amounts of fertilizer are required for large yields of potatoes. The use of manure, however, may increase the  incidence of potato scab. Ideally, the fertilizer should be placed in continuous bands 2–3 inches to each side and slightly below the seed piece. However, many gardeners will broadcast the fertilizer before tilling or spading. Fertilizer rates should be based on results of a soil test; a typical rate would be two and a half to three pounds of 8-16-16, 10-20-20, or equivalent per 100 square feet. When plants are 4–6 inches tall band 2–3 pounds of fertilizer per 100 feet of row about 6–10 inches from the row.

Cultivation

Control weeds by shallow and frequent cultivation; deep cultivation may cut potato roots and slow growth.  When plants are 6–8 inches tall begin to mound soil around the bases of the plants to start forming a ridge or hill. By the time the plants are 15–18 inches tall (at last cultivation) the ridge or hill should be 4–5 inches high. "Hilling up" is necessary to prevent greening of shallow tubers.

Insects and Disease

Flea beetles, leafhoppers, aphids, and Colorado potato beetles are the most common insects affecting leaves and stems. Early blight and late blight are the common foliar diseases of potatoes. Garden area previously in sod may harbor wireworms, white grubs and other soil insects, which should be controlled before planting potatoes.

Harvesting and Storage

For highest yields and best storage potatoes should not be dug until two weeks after vines have naturally  died back. This allows the skins to set and reduces skin peeling, bruising, and rot in storage. When harvesting at temperatures above 80oF potatoes should be picked up immediately and put in a dark place. Potatoes exposed to sun and high temperatures will turn green and may rot. Green skins on potatoes should be peeled off to reveal white flesh before cooking.

Most homes do not have a suitable place to store potatoes for more than four to six weeks. To store potatoes for several months the tubers should be cured in a dark place at 60–65oF and a humidity of 85 percent or higher for 10 days. After the tubers are cured keep them in a cool (40–45oF), dark place with high humidity. Most varieties will not sprout for two to three months under these conditions.

Adapted from E.C. Wittmeyer, Marianne Riofrio and Mark Bennett, Ohio State University Extension, 2000