Potatoes... from garden to table

FN-630, February 2006

Julie Garden-Robinson, Ph.D., L.R.D., Extension food and nutrition specialist
Asunta (Susie) Thompson, Ph.D., potato breeder
Duane Preston, Extension potato specialist, NDSU and UMN Extension

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Home-grown potatoes, or those purchased at a farmers market or other venues, are a nutritious part of a healthy diet from early July until the following spring in northern areas.

Cultivar Selection

Potato cultivars vary in appearance, maturity, growing requirements and culinary quality, and are an excellent source of nutrients, such as potassium. Potatoes are versatile and convenient. You can prepare them as baked, boiled, chipped, fried and roasted, and use them in soups, salads and stew.

Choose cultivars that suit your culinary needs and those suited to your local growing conditions. Most early cultivars will provide you with “new” potatoes, often by the Fourth of July. Those with a later maturity will require 100 days or more from emergence to produce a potato crop with acceptable yield. Table 1 lists some of the cultivars suitable for production in northern Plains gardens.

Skin or flesh color does not necessarily determine the best use of a potato cultivar; instead, the texture of the tuber determines the best use. Cultivars that are high in starch content, or dry matter, are mealy, tend to bake with a fluffy texture and make excellent fries and chips due to low oil absorption and generally light color. Those with a waxy texture are lower in starch content and specific gravity, and frequently higher in sugar content. These cultivars hold together better during boiling and are preferred for salads, soups and stews.

Red-skinned cultivars

Red-skinned cultivars provide an attractive contrast to meat and other vegetables, and tend to have lower starch content and a waxy texture, making them most suitable for boiling, roasting, salads, soups and stews. They may have a sweet flavor, particularly after cold storage. Typically, they are round, although oblong or oval cultivars are becoming common. The majority have white flesh. Several new cultivars, particularly those from Europe, have varying shades of yellow flesh. Some consumers feel these have a “nuttier” flavor. Red-fleshed, red-skinned cultivars also are finding a niche in garden catalogs, garden centers, farmers markets and upscale restaurants.

White-skinned cultivars

White-skinned potato cultivars may be high or low in starch content. Those with high levels tend to have a mealy texture and are most suited to chipping or frying, particularly if they accumulate low levels of sugar during growth and storage. Those with lower levels have a more waxy texture, thus hold together better during boiling or roasting. Typically, white-skinned cultivars have white flesh; however, shades of yellow predominate the majority of cultivars popular in Europe, Mexico and South America. Yukon Gold, a very versatile, yellow-fleshed cultivar, is widely adapted and the most popular in North America.

Russet-skinned cultivars

Russet cultivars are characterized by their brown, netted skin. The majority of cultivars are oblong to long. Dual-purpose cultivars are suited for making french fries and other frozen processed products, as well as for baking. These cultivars tend to have high dry-matter content, and several accumulate low levels of sugar, making them suitable for processing. Some cultivars, such as Russet Norkotah, are widely adapted, but have lower dry-matter content, making them useful for baking and American fries.

Production

Seed

Potatoes in the home garden and producer fields are grown from pieces of tuber containing “eyes.” This is called vegetative reproduction. You may grow potatoes from true botanical seeds, which are found in small berries similar to small tomatoes on the top of some potato plants. However, due to the complex genetic nature of the potato, these seeds will not produce a uniform crop in terms of appearance, yield and quality. In northern climates, the length of our growing season would be too short.

Whole tubers or cut seed pieces should weigh about 2 ounces or slightly more. Cut seed should be planted immediately if soil conditions and temperature permit, or healed for three to four days in the dark at room temperature and high humidity (90 percent or higher, but with no condensation). Do not expose cut seed to hot temperatures or let it dry out. Sources of seed potatoes for home gardeners are local garden centers and seed catalogs. Check with your local Extension office to be sure no restrictions apply on purchasing seed imported from out of state. Purchase certified seed potatoes, as these have been inspected for disease presence and quality. Warming the seed tubers to 50 to 65 F prior to cutting will encourage germination and sprout growth. Seed pieces with sprouts c to ¼ inch are ideal and will emerge rapidly under proper conditions.

How much seed do I need? For each 100 feet of row, you will need about 15 pounds of seed.

Can I use potatoes from the grocery store as seed? Potatoes from the produce section at a local grocery store are not suitable. Most have been treated with sprout inhibitors to prevent the tuber from sprouting and forming a healthy plant.

How do I cut seed? If cutting tubers for seed, pieces should weigh 1.5 ounces or more, be about the size of a golf ball, and contain two or three eyes. Use a sharp, clean knife to cut whole tubers. Do not use serrated knives as this leaves a ragged edge, slowing wound healing, and thus permitting pathogens to potentially enter the tissue and cause decay. A 10 percent solution of regular household bleach (1 ounce bleach to 9 ounces water) makes a good dip for sterilizing the cutting knife.

Planting

Plant potatoes up to two weeks earlier than the average date of the last frost. The soil temperature should be 45 F or warmer. Potatoes grow well in many soil types, though well-drained, sandy loams tend to be best. The soil should be tilled to a depth of 16 inches and preirrigated to form a moist seed bed.

Plant potatoes in rows 30 to 36 inches apart. Space seed pieces within the row at 10 to 12 inches and about 4 inches deep. You may form hills at planting, or within the following four weeks. Hilling provides space for the developing tubers and also helps prevent greening.

In your garden, 100 feet of row may produce in excess of 200 pounds of potatoes.

 

Fertilizing

Home gardeners may apply commercial fertilizer or well-rotted manure to the seed bed. If the manure is not aged well, it can burn the potatoes and possibly introduce diseases and weed seeds. It should be applied the fall before planting. Manure generally promotes common scab on tubers. Fertilizer should be placed in a band 2 inches below and about 2 inches to the side of where the seed will lie. Avoid putting the fertilizer in direct contact with the seed, as this may result in burning of sprouts or other damage. If plants appear to be turning yellow-green in midseason, you can apply granular nitrogen to the sides of the hills and lightly rake it in, or apply it with the irrigation water. Avoid overapplying nitrogen, as that may delay tuber development in favor of vine growth, resulting in lower yield. The best way to determine soil fertility levels and fertilizer needs is to take a soil sample prior to planting.

How much fertilizer do I need? Potatoes use about a pound of nitrogen for each 100 square feet of garden space.

What type of fertilizer should I use? Select a complete fertilizer such as 15-30-15, which contains 15 percent nitrogen, 30 percent phosphorus and 15 percent potassium.

Irrigation

Soil should be kept moist, but not wet, for successful potato production. Potatoes have a fairly shallow root system, about 18 inches deep. They need abundant oxygen and don’t perform best in compact soils. They take the majority of soil water from the top 12 inches of soil. Be careful not to overwater during the first few weeks after planting. When potatoes emerge, supplement rainfall with irrigation so plants receive moisture about every five days. The soil should be damp to a depth of about 2 feet. Subjecting potato plants to water stress will decrease yield and result in misshapen tubers. Indicators of stress include wilting leaves and dark grey-green foliage. Maximum water use occurs during rapid tuber development. When vines start to yellow and die, reduce watering to prevent maturing tubers from being predisposed to rotting.

Pests

Weeds – The easiest weed control in the home garden is hoeing, pulling and/or light cultivation before vines reach 8 to 10 inches in height. Avoid cultivation beyond this stage as damage to roots, stolons and developing tubers may occur, resulting in yield loss. Potato plants are better able to compete with weeds at this stage, reducing the need for much additional weed control. The most common weeds in the home garden include red root pigweed, kochia, lambsquarters and occasionally nightshade. If you find quackgrass or Canada thistle, contact your local Extension educator or garden supply store for control information.

Diseases – Potato diseases may be seed-borne, soil-borne or acquired during the growing season. To avoid many of them, purchase certified seed potatoes. Promptly remove any plants that are small, yellowing or sickly. The most common diseases in the home garden include common scab, early or late blight, pink rot and black scurf. They are summarized in Table 2.

Insects – Common insects in the home garden affecting potatoes may include aphids, flea beetles, Colorado potato beetles, wireworms and grubs. Most can be treated with insecticides, or insecticidal soaps for those preferring organic methods. You also can remove the Colorado potato beetle by hand if the garden area is small.

Harvest

You can harvest and use potatoes in the home garden during the growing season as new potatoes or in the fall after the plants have matured. Farmers use desiccants to dry potato vines to make harvest easier; however, this is not necessary in the home garden. You should use new potatoes quickly after harvest because the thin, immature skins allow rapid moisture loss and disease pathogens can infect them more easily. For storage, dig potatoes after fully matured and the skin is set. Skins will be difficult to remove when rubbed. Lightly irrigating prior to digging may soften dirt clods and reduce potential bruising and tuber damage during harvest. Potatoes dug from warm soil (50 to 65 F) generally will not bruise as easily as those dug from cold soil (45 F and below).

Storage

Potatoes should be stored in a cool and humid place. Initially, potatoes should be stored at temperatures of 50 to 60 F and high humidity (about 95 percent) for two or three weeks to permit the skin to cure and wounds to heal. For long-term storage (up to nine months or longer) in the upper Midwest, you should drop temperatures gradually to about 38 to 40 F prior to Dec. 1. You should maintain this temperature through the winter storage season. Good air circulation will reduce storage rots and sprouting, but humidity levels should remain high to minimize shrink due to moisture loss. The presence of condensation will encourage rotting.

What’s the best place to store potatoes? Store potatoes in a cool, dry place for best quality and longest shelf life. Don’t wash potatoes before storing because moisture speeds spoilage. When stored between 45 and 50 F, potatoes will stay fresh for several weeks. At room temperature, potatoes will retain their best quality for about one week. Avoid storing raw potatoes in the refrigerator because potato starch can change to sugar. This can result in excessive browning during cooking (especially frying) and an undesirable sweet flavor. Do not store potatoes close to fruit. Ripening apples and other fruit give off ethylene. Ethylene is a plant hormone that encourages potatoes to sprout prematurely. Do not store potatoes where they will be exposed to light. Potato tubers are botanically a modified stem; light causes them to green.

 

Questions and Answers About Potatoes

Are potatoes nutritious?
Potatoes are a nutritional bargain. A 5a-ounce potato has about 100 calories, no fat, 26 grams carbohydrate, 3 grams fiber, 21 percent of the daily recommendation for potassium, 45 percent of the daily recommen- dation for vitamin C, and other nutrients, too. Americans are falling short in potassium, vitamin C and fiber intake, among others.

Foods, such as potatoes, that are good sources of potassium and low in sodium may reduce the risk of high blood pressure and stroke. - Food and Drug Administration

A medium potato has as much vitamin C as a tomato. Vitamin C is an antioxidant nutrient that helps keep skin and gums healthy and helps the body absorb iron.

 

Are potatoes “fattening”?
No, a potato the size of a computer mouse (5a ounces) contains only about 100 calories. Nutrition labels are based on a 2,000-calorie daily diet, so a potato would be one-twentieth of the daily calorie needs of an average adult. The complex carbohydrates in potatoes provide energy to fuel our muscles and brain.

Think about your toppings! Potato toppings can add excess calories and fat, so consider using “reduced-fat” or “light” products or use smaller amounts of higher-fat/calorie toppings (see Table 3). For example, a 100-calorie potato with no fat becomes a “stuffed potato” with 463 calories and 35 grams fat when you add 2 tablespoons of butter, ¼ cup of cheddar cheese and 2 tablespoons of bacon bits. Over time, excess calories from any source can result in weight gain.

How should I select potatoes?
Look for firm, smooth potatoes. Avoid potatoes with wrinkled skin and soft, decayed areas, cuts or bruises.

Are any food safety issues linked with potatoes?
Improperly stored baked potatoes and rehydrated potato flakes have been linked to foodborne illness cases; however, you can take simple steps to prevent food safety issues. Wash potatoes thoroughly before cooking, using a clean vegetable brush if necessary to scrub them. Don’t use soap on produce because it can leave residues.

Most food safety issues linked with potatoes and other starchy foods (such as rice) result from improper cooling. These are steps to keep potatoes safe:

• Keep “hot foods” hot during serving (at least 140 F).
• Place leftover baked, boiled or mashed potatoes in shallow containers and refrigerate at 40 F promptly. Cooked potatoes and other perishable foods should spend no more than two hours at room temperature, according to U.S. Department of Agriculture recommendations. Unwrap leftover foil-wrapped baked potatoes before refrigeration and cut in half to speed cooling.
• Use leftover potatoes within three days. Freezing leftover potatoes is safe, but it isn’t recommended because of quality issues. Potatoes frozen at home may become somewhat watery because potatoes are more than three-fourths water by weight. During freezing, the water may separate from the starch.
  

A medium potato with skin contains 720 milligrams (mg) of potassium -- more than a medium stalk of broccoli (540 mg) and nearly twice as much as a medium banana (400 mg). Potassium helps muscles contract and the body maintain blood pressure.

To preserve nutrients and fiber, cook potatoes in their skins and eat the skin, or peel as thinly as possible. Many of the nutrients are directly beneath the skin in an area known as the “cambium.” To help prevent nutrient loss during boiling, use as little water as possible and a tight-fitting lid to avoid loss of water during cooking.

Why do potatoes sometimes get green spots on their skin?
When potatoes are exposed to natural or artificial light, they can become green. The green color comes from chlorophyll, a pigment naturally found in potatoes. Along with “greening” or sprouting, a compound called “solanine” forms. Solanine is one of the compounds that give potatoes their taste. In high amounts, however, solanine has a bitter taste and can be toxic. Avoid eating the green skin; simply trim and discard the green part of the potato before using.

Can I eat potatoes that sprout?
Yes, the potatoes still are edible. Just remove and discard the sprouts. To help prevent sprouting, store in a cool, dry, well-ventilated spot.

Recipes and Tips

Potatoes are a versatile menu item. You can bake, boil, microwave, grill, fry and steam them. They’re available in a variety of forms at the grocery store, including fresh, canned, instant and frozen. They’re nutritious and easy to prepare, and you can top them with a variety of items, including leftover chili or seasoned meat.

For a quick meal, try these potato toppers:

• Shredded cheddar cheese, chopped green onion and reduced-fat sour cream
• Chili with beans
• Taco meat, salsa and reduced-fat Mexican-style shredded cheese
• Spaghetti sauce and parmesan cheese
• Leftover chopped roast pork or beef with barbecue sauce
• Grilled chicken and ranch dressing

  
  

  One Potato, Two Potato… Potato Equivalents One pound of potatoes equals • 3 medium-sized (about 5-ounce) potatoes • 3 cups peeled and sliced • 2¼ cups peeled, diced • 2 cups mashed • 2 cups french fries

Baked Potatoes

Preheat oven to 400 degrees. Wash potatoes thoroughly, pierce with a fork in several spots and bake approximately 40 to 45 minutes until soft. If you are baking potatoes with other items at lower oven temperatures, adjust baking time.

Microwave-baked Potatoes

If baking more than one potato in a microwave at a time, choose uniform-sized potatoes to allow for uniform cooking. Wash, dry and pierce potatoes with a fork or knife to allow moisture to escape. Arrange potatoes like petals on a flower on a microwave-safe pan or paper towel, leaving about an inch between potatoes. Cooking time varies depending on the size of the potato and the microwave oven. Check the microwave oven manual for more information. These are some estimated times:

 

Number of potatoes	Approximate minutes to bake in microwave
1	4 to 5
2	6 to 8
4	13 to 15
6	17 to 19

Turn the potato midway through cooking. Check for doneness by piercing the potato with the tip of a sharp knife.

Onion Roasted Potatoes

1 envelope onion soup mix
2 pounds potatoes, cut into large chunks
a c. olive oil or vegetable oil

Preheat oven to 400 F. ??Wash potatoes thoroughly. Peel if desired. Place ingredients in large plastic bag. Close bag and shake until potatoes are coated evenly. Empty potatoes into shallow baking or roasting pan. Discard bag. Bake potatoes, stirring occasionally, 40 minutes or until they are tender and golden brown. Garnish, if desired, with chopped parsley.

Makes eight servings. Each serving has 184 calories, 22g carbohydrate, 9.6g fat, 2.7g fiber and 409mg sodium

Oven Fries

4 medium potatoes, peeled and cut in strips
2 Tbsp. salad oil
Salt
Paprika (if desired)

Preheat oven to 450 F. Wash potatoes thoroughly and peel. Place strips in a bowl of ice water to crisp. Drain and pat dry. Place strips in an even layer on jelly-roll pan. Sprinkle with oil. Shake pan to distribute oil evenly over potatoes. Bake at 450 F until golden brown and tender, about 30 minutes, turning frequently. Sprinkle with salt and paprika if desired.

Alternate instructions for easy cleanup: Wash potatoes, leaving on the peel. Cut into strips and place into a large plastic bag. Add the oil and seasonings. Shake to coat. Place strips on jelly-roll pan. Discard bag. Bake potatoes.

Makes four servings. Each serving has 224 calories, 37g carbohydrate, 7g fat and 4.7g fiber. Sodium varies depending on amount of salt added.

Rosemary Roasted Potatoes

1 pound small, red potatoes
2 Tbsp. olive oil
½ tsp. crushed, dried rosemary
½ tsp. salt

Preheat oven to 400 F. Wash potatoes thoroughly. Cut in half. Arrange in shallow pan. Drizzle with olive oil and turn to coat well. Sprinkle with rosemary and salt. Stir to mix well. Bake uncovered in a 400 F oven, stirring occasionally, until tender (25 to 35 minutes).

Makes four servings. Each serving has 145 calories, 18g carbohydrate, 7.2g fat, 2g fiber and 298mg sodium.

Potato Packets for the Outdoor Grill

4 large, red potatoes (about 1.5 pounds), cut into 1½-inch chunks
2 Tbsp. olive oil or vegetable oil
½ tsp. salt or seasoned salt
½ tsp. ground black pepper
Heavy-duty aluminum foil or 1 large extra-heavy-duty foil cooking bag

Variations — Add one of the following ingredients: ¼ c. chopped green onions, one chopped jalapeno chili pepper with seeds removed or ¼ c. chopped cilantro.

Prepare outdoor grill. Place two 30-inch by 18-inch sheets of heavy-duty foil to make a double thickness. Place potatoes, oil and seasonings in center of foil. Bring short sides up and fold over several times to seal well. Gently shake to combine ingredients. (Or, place recipe ingredients in foil bag, seal and shake to combine.) Place bag on hot grill rack, cover and cook 15 minutes. Carefully turn the bag over using tongs or another utensil to avoid burns, then cook another 15 minutes. Remove from grill and cut slits in bag, allowing steam to escape. Carefully open and transfer mixture to a platter.

Makes four servings. Each serving has 186 calories, 27g carbohydrate, 7.3g fat, 3g fiber and 301mg sodium.

Skewered Grilled Potatoes

2 pounds red potatoes, quartered
½ c. water
½ c. light salad dressing, such as Miracle Whip
¼ c. chicken broth
2 tsp. diced oregano leaves
1 tsp. garlic powder
½ tsp. onion powder

Place potatoes and water in 2-quart casserole; cover. Microwave on high 12 to 15 minutes, stirring after eight minutes. Drain. Mix remaining ingredients. Stir in potatoes and cover. Refrigerate one hour. Prepare charcoal grill. Remove potatoes from salad dressing mixture and place on skewers. Grill, covered, for four minutes. Rotate skewers and brush with reserved salad dressing mixture. Continue to grill for four minutes.

Makes eight servings. Each serving has 121 calories, 21g carbohydrate, 3.2g fat, 2.2g fiber and 154mg sodium.

Garlic Mashed Potatoes

1 pound red potatoes
½ c. skim milk
2 large garlic cloves, chopped
½ tsp. white pepper
1 Tbsp. fresh chives, chopped (optional)

Peel potatoes, cut into quarters and place in cold, salted water for about 15 minutes. Drain in colander, rinse well and place in 2-quart saucepan containing 2 cups of boiling water. Cover and cook for 20 to 25 minutes or until tender. Meanwhile, have milk warming over low to medium heat. Add garlic to hot milk and simmer until garlic is soft, about 20 to 25 minutes. Remove cooked potatoes from heat, drain in colander, replace in saucepan and cover to keep warm. Add milk-garlic mixture and white pepper to potatoes, mash with potato masher and then whip with an electric mixer. If desired, garnish with chopped fresh chives.

Makes four servings. Each serving has 96 calories, 20.3g carbohydrate, 0.2g fat, 2g fiber and 23mg sodium.

Old-fashioned Lefse*

4 c. mashed or riced white potatoes
a c. butter
1 Tbsp. sugar
1¼ c. milk
1¼ tsp. salt
1¼ to 1½ c. flour

Mix first five ingredients. Refrigerate until thoroughly cool. Add flour gradually and knead smooth. Depending on the size of your pan or lefse grill, take a small handful (about a c.) and roll paper thin on a floured surface. Bake on a hot griddle until golden spots form. Turn and bake on second side. Place flat on a clean towel and cover with another towel. Place several sheets of lefse on top of each other. When cool, cut into quarters or halves and place in plastic bags to preserve freshness. Note: Be sure dough remains cold until you are ready to roll it. Makes 15 large lefse.

Makes 30 servings. Each serving (about half a large round or 1.5 ounces) has 60 calories, 8.9g carbohydrate, 2g fat, 0.6g fiber and 69.7mg sodium.

*Lefse is a traditional Scandinavian bread, similar to a tortilla but made with mashed potatoes.

For more recipes, visit the U.S. Potato Board Web site, www.healthypotato.com.

For more information, visit these NDSU Extension Service Web sites:

Nutrition, food safety and health: www.ag.ndsu.nodak.edu/food.htm

Horticulture: www.ag.ndsu.nodak.edu/horticulture.htm

FN-630, February 2006