Potatoes
Potatoes (Solanum tuberosum) are one of the most widely consumed foods in the world, considered the fourth most important crop after
wheat, corn, and rice. Though the French coined the term “apple of the earth” or pomme de terre, potatoes were actually brought to
old-world countries by Spanish explorers.
The Incas discovered potatoes growing wild in the Andes Mountains and had been cultivating them for nearly two centuries for a variety
of food and medicinal purposes. Introduced to the Spanish in the 1500s, the explorers mistook potatoes for a kind of truffle, and took
them back to Europe. Acceptance, however, was slow; as part of the Solanacceae family (which includes some poisonous plants as well as
tomatoes, peppers, and eggplant), a few well-publicized poisonings—from Europeans eating the harmful green parts of the potato plant
(not the actual stem or potato)—resulted in widespread fear.
Today, potatoes are the U.S.’s top vegetable crop, with more than half being sold to processors for French fries and chips, dehydration, or
used for other potato products. The remainder, often referred to as ‘table potatoes’ are sold fresh, used for animal feed, or set aside as seed
tubers to grow new crops.
References: Agricultural Marketing Resource Center, Purdue University Extension, University of Illinois Extension, University of Minnesota
Extension.
SEASONAL AVAILABILITY
COLORADO
IDAHO
NORTH DAKOTA
WASHINGTON
WISCONSIN
CANADA
CHINA
INDIA
*Note: chart presents harvest months; potatoes from storage provide year-round availability.
References: North Dakota Department of Agriculture, Idaho Farm Bureau Federation, International Potato Center, Statistics Canada, University of
Wisconsin-Madison, USDA, Washington State Department of Agriculture.
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Potatoes
TYPES, VARIETIES & CUTS
Potatoes come in a wide variety of shapes, colors, and sizes. Fresh market spuds include white, russet, red, gold, fingerling, purple or
blue, mini, new, and yellow varieties. Potatoes with white flesh can vary widely in skin color, and there are a number of more exotic
types too, sporting deeply colored skin and even blue or purple flesh.
White potatoes, often called Irish potatoes, are commonly used for chips, French fries, and baking. Red-skinned potatoes with
white flesh are often used for mashed potatoes, while yellows, more common in Europe, are becoming more popular in the
United States. Potato skins vary widely from rough and thick to thin and smooth. Shapes range from round to oblong to the
narrower fingerling.
References: University of Illinois Extension, University of Florida IFAS Extension, Purdue University Extension.
PESTS & DISEASE
Potatoes are especially vulnerable to bacterial diseases when injured. Diseases specifically caused by poor preharvest practices or
postharvest handling include blackheart, black spot, chilling injury, greening, internal brown spot, and net necrosis. Other diseases of
concern when growing potatoes are blight, scab, fusarium wilt, bacterial soft rot, brown rot, and water rot. More serious diseases of
immature potatoes are pink eye and grey mold.
Pests of concern include leafhoppers, flea beetles, Colorado potato beetles, and root knot nematodes.
References: University of Illinois Extension, UC Davis Postharvest Technology website, University of Minnesota Extension.
CULTIVATION, STORAGE & PACKAGING
Preharvest:
Potatoes require cooler weather and ideally a long, cool season to thrive. Generally planted in early spring, potatoes are not seeded, but
are planted using portions of harvested potatoes that contain at least one or two buds or “eyes.” Potatoes require loose, fertile soil high
in organic matter and well drained. Soil temperature should be from 60 to 70°F. Growth stops at soil temperatures of 80°F or higher.
Planting is via hilling with 24 inches between rows; plants should be spaced about 12 to 18 inches apart. Seed potatoes are planted
eye-side up approximately 2 to 3 inches deep. Two weeks before harvest, growers may apply a chemical to dry up vines, which also kills
pathogens that might otherwise thrive in storage. Potato skins also mature during this step, so the crop is less likely to suffer bruising
and injury.
Postharvest:
Ideal harvest conditions are dry and cool, between 45 and 60°F. Drier soil decreases bruising from large soil clumps and minimizes
the detritus accompanying the crop, which can impede air flow in storage and encourage disease. Temperature fluctuations can make
potatoes more prone to injury, shrinkage, and water loss.
Some potato crops are harvested while immature, which increases susceptibility to bruising. Immature potatoes require more care
in handling and can only be stored for short periods. However, even late-crop potatoes are susceptible to bruising, which can cause
significant loss. Bruises and nicks allow microorganisms to take hold and spread; harvest equipment should be well maintained to
minimize drop height and rough handling.
After harvest, while in bins or trucks, containers should be covered as exposure to sunlight can cause greening, and to keep potatoes
from getting too hot. Crops are cured for 8 to 14 days at 50 to 60°F with 95% relative humidity. Depending on variety, potatoes can
be stored for several months at 39°F with 95 to 98% relative humidity, but less than three weeks is considered optimal.
Immature potatoes are cooled to 59°F, treated with sprouting inhibitor, and packed and shipped within one to five days. Storage also
varies depending upon the potato’s intended use. Fresh market potatoes are ideally stored at 45°F and 98% relative humidity; frying
potatoes between 50 to 59°F and 95% relative humidity; processing potatoes between 59 and 68°F and 95% relative humidity. Stored
potatoes should be cooled to the desired temperature gradually by decreasing temperatures about 5°F per week. Storing potatoes below
30°F results in chilling injury and rot.
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Potatoes
CULTIVATION, STORAGE & PACKAGING—CONTINUED
Cool, humid ventilation is crucial for potatoes in bins versus air-cooled storage rooms. Poor ventilation results in shrinkage,
sprouting, and decay. Too much airflow or too little humidity may cause weight loss. Potatoes are usually packed into perforated
plastic bags to promote air circulation while retaining moisture; they can also be packed in ventilated cardboard boxes.
Grades:
Potatoes are divided into U.S. No. 1, U.S. Commercial, and U.S. No. 2 grades.
References: Produce Marketing Association, Purdue University Extension, UC Davis Postharvest Technology website, University of
Minnesota Extension.
GOOD ARRIVAL GUIDELINES
Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the percentage of
allowable defects, provided: (1) transportation conditions were normal; (2) the U.S. Department of Agriculture (USDA) or Canadian
Food Inspection Agency (CFIA) inspection was timely; and (3) the entire lot was inspected.
U.S. Grade
Standards
Days Since
Shipment
% of Defects
Allowed
Optimum
Transit Temp. (°F)
10-7-2
5
4
3
2
1
14-[10 int, 10 ext]-3
13-[10 int, 10 ext]-3
12-[9 int, 9 ext]-3
11-[8 int, 8 ext]-2
10-[7 int, 7 ext]-2
50-60 (early)
40-50 (late)
Canadian good arrival guidelines (unless otherwise noted) are broken down into five parts as follows: maximum percentage of defects, maximum
percentage of permanent defects, maximum percentage for any single permanent defect, maximum percentage for any single condition defect, and
maximum for decay. Canadian destination guidelines are 15-15*-5-10-3 (the 15% permanent defects allows for no more than 3% hollow heart,
5% undersized, and 5% oversized potatoes).
References: DRC, PACA, USDA.
POTATOES: WEEKLY MOVEMENTS & PRICES, USA
Source: Chart by Gallo Torrez Agricultural Price Trends (GTAPT), [email protected], compiled from USDA data.
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INSPECTOR’S INSIGHTS
• At destination, not more than 5% of the potatoes may have sprouts longer than a half-inch in length, or clusters materially
affecting the appearance
• Silver scurf is scored as a defect, as damage, when more than 50% of its surface is affected
• Internal black spot, normally found affecting the shoulders and stem end, is scored as a defect when affecting more than 5%
of the total weight of the potato
• Size ‘A’ potatoes must meet a minimum diameter of 1.875 inches and at least 40% must be 2.5 inches in diameter or 6 ounces
in weight or larger.
Source: Tom Yawman, International Produce Training, www.ipt.us.com.
HEALTH & NUTRITION
Gluten-free potatoes are a good source of Vitamins B6 and C, potassium, and fiber. One medium potato provides 16% of daily
recommended fiber, 35% of recommended Vitamin C, 10% of recommended iron, and 620 mg of potassium which is more
potassium than a banana.
References: Produce Marketing Association, University of Illinois Extension, USDA.
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