Potatoes have changed. They aren't necessarily the same old gnarly brown spuds you find in the grocery store, not since nutritionists proclaimed potatoes the dieter's best friend, and not since nurseries have obliged by providing gardeners with new and exciting varieties.
Home gardeners can choose from more than 150 different kinds, a vast improvement over the 20 or so commonly available in our markets. Others are simply new to North Americans and are actually ancient in the South American homelands of the potato. You can grow potatoes throughout North America. Plant them anytime you can expect at least 60 days between hard frosts or periods of baking heat.
Potatoes are fun. It's downright delightful to slice open an 'All Blue' or a golden-fleshed 'German Butterball' for the first time, not to mention uncovering them as you harvest. Here's how to choose among these many varieties, when and how to plant, which pests to watch for and how to grow and harvest.
Botanically, all of our cultivated potatoes are descended from one species, Solanum tuberosum, which is native to temperate regions of the Andes. Produce buyers speak of five types: long white, round white, long russet, round russet and round red. Professional growers might add the "chippers" used for potato chips.
From a cook's point of view there are only two kinds of potatoes: thick-skinned kinds for baking and thin-skinned kinds for everything else. Baking potatoes are also known as "russets" for their rough brown skin, or as "Idahos" because so many come from Idaho. They have a dry, mealy texture suited to baking, but can also be fried, boiled or mashed. Thin-skinned potatoes have a creamier or waxier texture. They hold their shape after cooking, so are better suited to potato salads, boiling and steaming.
Fingerlings are small, thin-skinned finger-shaped tubers noted for their high productivity and good flavor. Admittedly, the colors are fun for their own sake.
'German Butterball' is the flavor choice of many potato aficionados. The skin is smooth and waxy flesh is golden yellow. It requires at least 90 days to mature. Yellow potatoes have been popular in Europe for generations, and several of the continent's favorites are now popular here. Most widely adapted is short-season 'Yukon Gold' (butter yellow flesh with rich flavor, 65 days to mature). It produces well throughout North America. 'Huckleberry' is one of the exciting red-red potatoes. It is a midseason type requiring 80 or more days to mature. Productivity is average, but that is more than compensated by the high visual appeal of its red skin and red flesh. Similar and widely recommended are 'All Red' (red skin, reddish flesh, 80 days), and 'Alaska Sweetheart' (red skin, pink flesh, 80 days). Potato salad will never be the same.
'Russian Banana' is a yellow-skinned, yellow-fleshed fingerling from the Baltics. Although fingerlings are long-season potatoes requiring 90 days or more in most climates, 'Russian Banana' grows successfully in short-season areas, though tubers will be smaller. 'Larota' and 'German Yellow' both have a particularly firm texture and unique flavors. 'French Fingerling' (purple-pink skin and yellow flesh) and 'Rose Finn Apple' (rosy-tan skin, yellow and red flesh) are also recommended.
'Bintje' (pronounced "ben-gee") is one of the most widely grown yellow-fleshed potatoes in the world. Developed in Denmark, it is the definitive waxy, gourmet potato in Europe. It grows well in most regions, requiring approximately 90 days. It produces average-size potatoes that, prepared by any method, have excellent flavor.
'All Blue' is the best blue-purple potato for most gardeners. Tubers are smallish and texture is dense. It matures in approximately 80 days.'Purple Peruvian' is similar but takes longer to mature. Its texture is mealier and it keeps in storage very well. Blue-skinned 'Glacier' (80 days) has white flesh with blue markings. 'Caribe' (65 days) combines lavender skin and white flesh with earliness, heat tolerance and productivity.
'Blossom' is perhaps the prettiest of these offerings: Delicate, thin skin encloses flavorful red and pink flesh. These narrow, tubular tubers require about 80 days to mature. Among the earliest red potatoes you can grow is 'Red Norland' (65 days). Its flesh is cream white. 'Red LaSoda' (80 days) is the red skin-white flesh market standard. 'Red Dale' (65 days) performs well in all climates. This big potato is a good baker, keeps well and is resistant to scab disease.
'Green Mountain' is a mealy-fleshed heirloom potato that's been grown in the Northeast for at least 100 years. Thin, tan skin covers mealy flesh that's excellent baked. It also stores well. 'Green Mountain' needs 90 or more days to mature. Standard white boilers include 'Katahdin' (90 days) and 'Kennebec' (80 days). The older (and disease prone) 'Irish Cobbler' (65 days) has excellent eating quality; 'St. John's' (90 days), introduced in 1993 by the University of Maine, has excellent disease resistance.
'Norkotah Russet' is a good example of a modern baking potato. An all-purpose potato, 'Norkotah Russet' was introduced in 1987. Growers in all regions rely upon it as it's excellent for baking or boiling. It requires about 65 days to mature. Other good russets for northern areas include 'Gold Rush' (80 days), 'Butte' (90 days) and 'Bake King' (80 days). Old reliable 'Russet Burbank' (80 days) grows best in long, consistently cool and moist regions of the Northwest. In southern regions, try newly released 'Century Russet' (75 days).
How to Grow Potatoes
Most often you plant "seed potatoes." These are usually sections of disease-free varieties. Larger potatoes are sectioned into pieces with at least two buds, or "eyes," each. An average-size potato has five to eight eyes, so yields two to four seed pieces. Smaller potatoes, such as fingerlings, are often planted whole. If you are cutting your own seed potatoes, allow them to cure or suberize a day or two before planting. This lets the cut surface heal somewhat and resist rot once in the soil. Or plant whole potatoes; they're less prone to rotting than cut seed pieces.
Presprouting cut (and cured) seed pieces before planting starts growth fast for earlier harvest and further helps prevent seed rot. Two to three weeks before the planting date, bring the potato pieces into a warm, bright room where they will begin to grow. (Handle these sprouts carefully on planting day.)
You'll need approximately 2 pounds of seed potatoes ($1 to $2) cut into 20 seed pieces to plant a 20-foot row. Fingerling seed pieces are smaller so you need only 1 to 1- 1/2 pounds. They cost approximately $2 per pound. (If you buy mail order, the cost of postage will double the price.)
A few nurseries sell tissue-propagated minitubers. These are tiny tubers developed from tissue culture ($1 each). They promise freedom from tuber-borne diseases, and are not cut before planting.
The variety 'Homestead' is one of very few potatoes that consistently yields a superior edible tuber from seed. Start seeds indoors 8 to 10 weeks before planting time. A packet of 50 seeds costs $1.40.
Plant, Water, Mulch
Plant potatoes in well-drained, fertile soil and in full sun. If you regularly add compost, no additional fertilizer is necessary. If not, mix in organic matter and 4 pounds of a 5-3-4 organic fertilizer (or equivalent) per 100 square feet before planting. Avoid nitrogen applications greater than this both before and after planting.
Plant pieces containing at least two buds 4 inches deep and 8 to 14 inches apart in a shallow trench in soil, or under a 4-inch layer of leaf mold or straw. (The mulch method is useful in heavy soils.) Allow 2 1/2 to 3 feet between rows of mid- to late-season varieties, 12 to 18 inches for early kinds.
Maintain consistent soil moisture; fluctuations can cause misshapen tubers and other problems. No matter when you plant, if you live where rainfall is infrequent, or nonexistent for periods, plan on providing supplemental water.
As the stems begin to elongate, mound soil or lay mulch around their bases. This is called "hilling" and is necessary to keep roots cool and moist for developing tubers and to prevent light from reaching them. Hill when plants reach 6 inches and again at 12 to 15 inches.
Exposure to light promotes production of chlorophyll along with various toxic glycoalkaloids, such as solanine and chaconine, in the skins of the developing tubers. When the skin is green, the tuber is unfit to eat.
Hill with Soil or Mulch
Last summer eight National Gardening test gardeners grew one row of Katahdin potatoes hilled with soil, and one row mulched with straw.
The results were one-sided and surprising. From Massachusetts to California, on clay soil or sandy soil, in wet weather or dry, the potatoes hilled with soil outyielded the potatoes mulched with hay, straw or leaves by an average of one-third, and generally produced larger tubers.
According to Ed Plissey, potato specialist at the University of Maine, Orono, "Soil is a better buffer of fluctuating soil moisture than mulch is, so I'm not surprised hilled rows outperformed those that were mulched," says Plissey. "For potato tubers to set properly, the soil has to be uniformly moist. If it's too wet or dry, the stolons won't form tubers and your yield is reduced," he explains.
"The small size of the mulched tubers is harder to explain, but I'd guess it is due to a lack of nitrogen," Plissey adds. "Microorganisms that decompose mulch use soil nitrogen as they work. If the soil has only marginal nitrogen levels, a deficiency can occur, which would explain the small tubers."
Conclusion -- Potatoes hilled with mulch are easier to harvest and produce clean tubers, but fewer of them. Also, some additional fertilizer may be necessary for tubers to achieve good size.
A midsummer planting, though not ideal, avoids the scourge of Colorado potato beetles. Many gardeners in the South and middle Atlantic states report great success with the following method: Arrange for late delivery of seed potatoes, and refrigerate them until planting time. Keep the soil in the planting bed cool by covering it with a thick mulch. Plant mid-July and harvest late October.
Although you can harvest anytime after the vines have flowered, dig tender "new" potatoes right after flowering begins and use those tubers immediately. Do this by reaching into the soil under the plant and feeling for the tubers. Carefully break them free from the plant and pull them out. Don't harvest more than two from one plant as that might retard its growth.
Harvest and Storage
Soil and air temperature, moisture, cloud cover, and variety all affect time to maturity. It is far from an exact science. Some varieties in certain regions may mature in two months, or less. Others may require three or more months. Typical season lengths are noted for each variety recommended, but these can vary by more than two weeks in either direction.
In the North, leave tubers in the ground one to three weeks after frost kills the vines. This toughens their skins. In the South, or where frost isn't as cooperative, knock vines down, then wait two weeks before harvesting to let skins set. If plants regrow, break them back again; also cut back on water.
To harvest, gently insert a garden fork a few inches from the plant and lift to loosen the tubers. Or simply pull back the mulch. If using tools, harvest carefully. A speared spud must be used right away or sacrificed.
After digging, let tubers air dry for at least two hours on a sunny day. Store potatoes in a dark, cool and humid environment. Ideal is 38° to 40° F and 85 to 90 percent humidity.
Yield is 6 to 12 times the amount planted. Hence, 10 pounds planted becomes 60 to 120 pounds at harvest. Fingerlings are even more productive.
Occasionally plants produce 3/4-inch berries in clusters of 5 to 10. These are the seed-bearing fruit of a potato plant. Some varieties are more likely to produce seeds than others, and their presence has no effect on developing tubers. They are poisonous to eat but are safe to handle. You can start your own potatoes from the seeds inside, but you'll get a hodge-podge of potatoes at harvest.
In cool, damp weather, late blight (Phytophthora infestans) can destroy a potato patch in a matter of days. Worldwide, it is the most devastating potato pest, usually controlled in the United States with fungicides, hygiene and quarantine. Weather conditions have to be just right. When they are, the disease progresses quickly. First symptoms are a cottony, white growth on the undersides of the leaves in combination with bluish "water-soaked" leaf lesions.
A new form of the disease, known as the A2 strain, came into the United States from Mexico or Central America around 1990. It is threatening because it will sexually reproduce with the existing A1 strain and create unpredictable progeny. Until now, growers contended with only one, genetically identical strain. This spring, Purdue University researchers announced a genetically engineered late-blight-resistant potato, but it is not yet commercially available.
Early blight (Alternaria solani) is a fungus that appears as concentric lesions on the leaf accompanied by weakening of the vine. It can overwinter in soil, but is easily controlled with copper sulfate and other fungicides, and is usually not lethal.
Rotation is essential to control Verticillium wilt, a soilborne fungus that causes yellowing and wilting of the vines and reduced tuber production. Superior, Kennebec, Russet Burbank and Norkotah Russet are susceptible to this fungus.
Scab (Streptomyces scabies) is another soilborne fungus. It causes corky patches on potato skins and is most common in soils that are dry and only slightly acidic. Control it by keeping soil pH at the low end of the optimum growth range, 6.2 or less, and by maintaining even soil moisture, particularly during the month after flowering begins. Katahdin is one of the few recommended varieties highly susceptible to scab.
Hollow heart is just what its name implies. A physiological disorder that causes brown discoloration of the flesh, it occurs when moisture is uneven or growth very rapid. It is more common in large tubers.
Heat necrosis, a discoloration of the tuber, is problematic in the South. Avoid it by growing early-season varieties and planting and harvesting before the hottest times of year.