Since the average American eats about 125 pounds of potatoes and potato products each year, Irish potatoes are one of America’s most popular vegetables. Irish potatoes are a cool-season crop; they grow best in early spring and late fall when the days are warm and the nights are cool. Although the potato is a cool-season crop and the edible part of the plant is an underground stem called a tuber (not a root), the tops of the plant will not withstand frost. Potatoes need full sun for best production.
Soil Preparation and Fertilization
Potatoes do best in a loose, well-drained, slightly acid soil. Poorly drained soils often cause poor stands and low yields. Heavy soils can cause tubers to be small and rough.
Remove rocks, large sticks and trash from the soil before spading. Spade the soil 8-12 inches deep. Turn the soil over to cover all plant material. Work the soil into beds 10-12 inches high and 36 inches apart. Bedding is very important for drainage.
Because potatoes need adequate fertilizer in early season, apply most of the fertilizer just before planting. Use two to three pounds of complete fertilizer like 10-20-10 for each 30 feet of row in bands two inches to each side and one inch below the seed piece. The fertilizer should not touch the seed piece. To apply the fertilizer, flatten the beds so they are six to eight inches high and 10 to 12 inches wide.
Using the corner of a hoe or stick, open a trench about four inches deep on each side of the bed. Apply half of the fertilizer (about two cups for each 30 feet of row) in each trench. The seed pieces will be planted in a row between the two bands of fertilizer.
Preparation of Seed
Irish potatoes are not grown from seed like most other vegetables. Instead, pieces from the potato itself start new plants. Home gardeners should purchase good seed potatoes free of disease and chemicals. Do not buy potatoes from a grocery store for planting.
The seed potato contains buds or "eyes" which sprout and grow into plants. The seed piece provides food for the plant until it develops a root system. Too small a seed piece produces a weak plant. Large seed potatoes for the spring crop should be cut into pieces which weigh about 1 1/2 to 2 ounces (about the size of a medium hen egg). Each seed piece must have at least one good eye. Cut the seed five or six days before planting. Hold the cut seed in a well-ventilated spot so it can heal over to prevent rotting when planted in cold, wet or very hot weather. Plants killed by a late spring frost will not come back if the seed piece is rotten. One pound of seed potatoes will make nine to ten seed pieces.
Seed usually is more available in the spring than in the fall. Many gardeners choose to buy extra seed in the spring and hold it over for fall planting. To do this, keep the potatoes in a cool, humid spot like the bottom of a refrigerator. Do not save your potato seed more than one year. This can cause buildup of virus disease which will reduce yield.
Potatoes should be planted when the soil temperature four inches deep reaches about 50o F, or about three weeks before the last spring frost. Potatoes should be planted in February or early March. If planted too early the tops can be frozen off by spring frost. For a fall crop, plant about 110 days before the first expected frost.
Use a hoe or stick to open a trench about three inches deep down the center of the bed. Drop seed pieces 10 to 12 inches apart in the trench. Step on each seed piece after dropping it to assure good contact with the soil. Cover the seed about three inches deep. If covered too deeply, the plants will be slow to break through the soil and will be more subject to disease and seed decay.
The most common types of Irish potatoes are red or white. Most red varieties store longer than white varieties. Most white varieties have better cooking qualities than red varieties. Many gardeners plant some of each in the spring. The whites are used first and the reds stored for later use.
Care After Planting
All tubers produced on a potato plant come from above the seed piece. Since the seed piece is planted only three inches deep, soil must be pulled toward the plant as it grows. This allows a place for the tubers to form. Some gardeners use a thick mulch for this purpose. Tubers formed in a soft mulch often are smoother and better shaped than those grown in soil. This is especially true if the soil is heavy.
As the tubers enlarge they must be protected from sunlight. Exposure to sunlight causes them to turn green. A thick layer of mulch applied when the plants are eight to ten inches tall can reduce soil temperature and increase yield and quality.
The soil moisture supply should be kept constant during growth. The plant must have adequate moisture and fertilizer when the tubers are forming. This usually occurs when the plants are six to eight inches tall. Apply one cup of fertilizer for each 30 feet of row beside the plants when they are about four inches tall. Water the fertilizer into the soil. This is especially important on sandy soils.
Moisture stress followed by irrigation or rainfall can cause growth cracks and second growth. If the rainfall is accompanied by hot weather, the rest period of developing tubers can be broken and can cause the tubers to sprout in the soil. Too much water causes enlarged pores on tubers and makes them rot easily in storage.
Potato plants usually produce flowers and sometimes produce fruits. The fruits bear the true seed of the potato plant. They look like small tomatoes but cannot be eaten. Potato plants do not cross with tomato plants.
Harvesting and Storing
Potatoes are ready to harvest when the tops begin to die and the skin becomes firm on the potato. The skin is set when it does not scrape easily when rubbed with the thumb. Skin set can be speeded by cutting back the tops of the plants. Most of the potatoes should weigh 6 to 12 ounces at harvest. Harvest small, "new potatoes" during the growing season by carefully digging beside the plants with the fingers.
To harvest potatoes, dig under the plants with a shovel or spading fork. Keep the fork eight to ten inches away from the plant to prevent cutting the potatoes. Raise the plants and shake away the soil. Potatoes should be dug when the soil is moist. If it is too wet, the soil will stick to the potatoes. If too dry, clods will bruise the potatoes. Pull the potatoes from the vines and handle them carefully to prevent damage since damaged potatoes do not store well.
Allow the potatoes to dry, then store them in a cool spot with plenty of air movement. Most potato varieties are ready to dig 95 to 110 days after planting.
Potatoes are troubled by several diseases. Treatment of seed pieces with a fungicide prior to planting can be helpful.
A good rotation program is effective in controlling most potato diseases. If possible, do not plant potatoes in the same place more than once each three years. Do not follow or precede potatoes with eggplant, okra, pepper or tomato. Seed piece treatment is especially important if your garden is too small for adequate rotation.
Irish potatoes contain two percent protein and 18 percent starch. They are an inexpensive source of carbohydrates and provide a good quantity of vitamins and minerals when properly prepared. Green areas on potatoes should be peeled away before cooking.
After the potatoes are dug, place the tops in the compost pile. The spring potato crop often can be followed with a summer crop like Southern peas.