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Idaho Soil and Climate

High elevation, warm days, cool nights, and well-drained soil are ideal conditions for growing the best potatoes.

Plants adapt to environmental conditions through thousands of years of natural selection. The ancestors of today’s Idaho® russet potato as well as niche varieties were originally found growing on the slopes of the Peruvian Andes, where they had adapted to high elevation, warm days, cool nights and welldrained soil.

The native population of the area used the tubers produced by these wild potato plants for food before Spanish explorers took samples back to Europe in the 16th century. The cultivation of the plant soon spread throughout the European continent. These plants were brought back to North America in the 18th century.

Although plant breeders have changed many varieties of potatoes, the ever-popular Russet Burbank (one of the most famous Idaho® potatoes) retains its love for mountain climates where it grows best. In Idaho, the potato growing area varies from about 2,500 feet above sea level in the lower Snake River Valley to 6,000 feet near the river’s source in eastern Idaho. Because of this elevation, the climate during the growing season produces cool nights and sunny days, providing the warmth and photosynthetic energy that the plants need to grow a nutritious potato.

The leafy canopy of the potato vine transfers energy to the tubers when the temperature drops at night. Idaho’s climate has proven ideally suited to growing Russet Burbank and Norkotah Russets, as well as many other varieties.

Soil type also affects the character of potatoes. Rich, sandy loams are most suitable for producing the light, fluffy types favored by American tastes. The geological events that formed the mountain systems in Idaho are also responsible for the soil. Mountains formed by volcanic eruptions and the intrusion of granite-like batholithic rock have eroded and covered the river valleys with a light, well-drained soil, rich in the minerals needed to grow potatoes.

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Growing and Harvesting Idaho® Potatoes

The quality of Idaho® potatoes is a product of both the heredity of the varieties and the ideal environmental conditions under which a superior potato is grown. It typically requires 120–150 days to grow a crop of Idaho® russet potatoes—days of constant attention and hard work. The Idaho® Russet Burbank has proven very difficult to grow commercially but its superior quality and versatility make it well worth the effort.

The potato-producing area in the state of Idaho has natural attributes of elevation, soil, climate, and water that make it ideal for growing potatoes. Even with these advantages, growing the perfect potato requires substantial labor, knowledge, and expense.

The process begins in the autumn with soil preparation of fields to be used for potato production the following year. Typically, the land will have been in another crop in the planned rotation cycle, which is necessary to produce a bountiful yield of the best quality. Idaho farmers rotate the potato crop once every two to three years in order to balance the soil’s ability to produce a good yield.

Fall irrigation, plowing, and bedding of the soil help ensure the decomposition of grain straw from the previous crop and favor a clod-free texture with ideal moisture for planting in early spring. A grower may elect to use fertilizers in the field in the fall to aid organic decomposition and to save precious hours at planting time.

During the winter, the Idaho® potato grower will typically make arrangements to buy seed potatoes. These certified seed potatoes are specially grown to maintain ideal heredity type, organic vigor, and freedom from the many diseases that can ruin a crop.

The Idaho Crop Improvement Association, an objective third party, inspects all seed potato lots to ensure the highest standards. The seed may remain with the grower until the customer is ready to plant the crop in April or May.

Before planting, the tubers are cut into seed pieces, each of which must have at least one eye. The cut surfaces are sprayed or dusted to promote healing and discourage disease organisms. All chemical substances used in any phase of soil treatment or crop production are approved and licensed by the federal and state governments. These licenses are obtained only after extensive testing to establish the safety of the material for use on potatoes grown for food.

Major Idaho® Potato Growing Areas

Planting

A potato planter is a highly specialized agricultural machine that opens a furrow, places seed pieces at a predetermined spacing in the row, and covers them with soil. Each seed piece will sprout and produce a potato vine under which the tubers of the new crop will form and grow during the four months ahead. Growers often contend with rain, wind, and cold weather at planting time, usually in April to May. However, they time planting so that rising soil temperatures will enable sprouting and growth to begin immediately.

Irrigation

Summer’s rainfall is not sufficient in Idaho to grow most farm crops, so farmers have elaborate irrigation systems to supply the needed water. Idaho may only average 11–12 inches of moisture annually. Most of this falls as snow in the mountains during the winter months. As the snowpack melts, the water is stored in huge reservoirs, from which it is drawn as needed during the growing season. Some farms rely on wells that reach down into underground aquifers as deep as several hundred feet.

Sprinkler systems largely dominate surface irrigation techniques. The grower’s task is to maintain adequate moisture content of the soil within rather narrow limits. Too much water will hurt quality, while too little will stress the plants, causing irregular shapes and sizes.

Many Idaho® potato growers now utilize a management system that integrates air temperature, relative humidity, and natural precipitation into a measurement of the potato plant’s water needs. The timing and amount of irrigation are calibrated to maintain consistent soil moisture, which will produce the maximum yield and highest quality for the grower.

Other Horticultural Practices

Other factors that can influence the quality of an Idaho® potato crop are weeds, insects, and a variety of plant diseases. Competition from these elements during the growing season would seriously reduce quality and yield potential without the watchful eye of the farmer.

Weeds are controlled in potato fields by a variety of management practices. Herbicides are often applied to kill weeds both before and just after they emerge from the soil. Mechanical cultivation can destroy weeds as the grower builds up the soil along the rows of potato vines.

Insect pests that attack potatoes, both above and below the surface of the soil, come in many shapes and sizes. Some insecticides are applied as soil treatments and others are sprayed on the foliage as needed.

Potatoes are also vulnerable to a variety of bacterial, viral, and fungal diseases. The use of disease-free certified seed, combined with horticultural practices, can accomplish a big part of disease control. Some maladies such as blight, which caused the famous 19th-century potato famine in Ireland, may require the application of sprays at strategic times during the growing cycle. Any such treatment must be made with approved materials and proper application rates to ensure the purity of the harvested crop and to protect farm workers.

Plant nutrition is another extremely important area affecting the success of the Idaho® potato farmers’ efforts. Science again provides help, with soil sampling and analysis. Primary plant foods and trace elements that prove to be necessary are applied before and during the growing season to ensure healthy, highyielding plants. Another helpful scientific technique is tissue analysis, in which samples of foliage reveal falling levels of nutrients before they can damage the quality of the crop.

With so many factors to monitor and control, growing a crop of Idaho® potatoes is a demanding job. Potato farms in the Gem State vary from a few hundred to several thousand acres, and fields are visited daily to check the progress of the crop and look for signs of any potential problems.

Sustainability

Idaho growers have been farming for multiple generations. Taking care of the land is a top priority for the future of their sons and daughters.

Growers are continually trying to limit the amount of fertilizers, fungicides and pesticides that are needed to grow potatoes. This effort, combined with best practices such a crop rotation or using cover crops, is key to preventing disease, enhancing soil quality, and boosting the productivity of the crop.

The goal is a reduction in chemical applications. Growers seek alternative methods whenever possible. For example, integrated pest management means anticipating what may be needed and applying only what is necessary.

The days of carelessly applying needless amounts of any resources are over. Attention to better-integrated pest management can restore natural ecosystems, prevent erosion, support native plants and animals, conserve water quality, and improve production, often all at the same time.

Growers are required to follow EPA guidelines for any applications and are permitted to use only approved products for potatoes that are based on a reasonable certainty of doing no harm.

Growers are improving their water use efficiency and irrigation methods, often considering the type soil, the section of the field and the timing of water applications.

Compared to their counterparts 100 years ago, today’s U.S. potato growers are able to produce three times as much volume on one-third of the acreage.

Harvest

Some of the quality attributes of potatoes and their ability to store well are dependent on maturity. Potato vines, under most conditions, will continue growing until killed by freezing weather. The tubers under the ground are not ready to harvest immediately when the vine dies, but should remain in the soil for about two weeks to fully mature. During thisperiod, the skin is toughened and the physiological factors of the tubers adjust to a period of dormancy. Most growers kill potato vines to allow sufficient time for the tubers to mature and harvest to be completed before cold weather arrives. Vine killing by mechanical or chemical means usually begins in Idaho in mid-August to early September.

The scale of commercial potato production in Idaho demands that mechanical harvesting methods be used. Digging potatoes is a labor-intensive project at a time of the year when the farmer is racing against the coming cold weather to get the crop into storage.

The potato harvester is a specialized piece of farm equipment. Pulled by a large tractor, the harvester digs underneath the potato hills and lifts the potatoes onto a chain elevator, where they are separated from undersized tubers and soil, most of which falls through the chain. The potatoes are further elevated by a series of conveyor chains. Dead vines and debris are removed mechanically or by the hands of workers riding the harvester.

Another elevator/conveyor belt, called the boom, delivers the freshly dug tubers into a truck, which is driven alongside the moving harvester. As one truck is filled, another moves into position to take its place. The filled trucks are driven to a potato storage facility, where they are mechanically unloaded. As potatoes pass over a conveyor, any remaining clods, debris, and vines are removed. The freshly harvested potatoes are piled several feet deep in the storage facility, where they will spend weeks or months until removed for packing and shipping to the consumer.

Storage

One reason the Idaho® potato has become such a favorite worldwide is because it is available the entire year. It is an extremely versatile vegetable, packed with nutritional food value, and is a key volume category for the supermarket or restaurant.

This year-round availability of potatoes from Idaho is due not only to the nature of the potato itself, but also to the large number of modern storage facilities that have been built across the state, and the availability of scientific knowledge about storage conditions.

The potato tuber remains a living organism even though its vine has died. After being removed from the ground and placed in storage, the tubers enter a period of dormancy and under the proper conditions of temperature and humidity, remain so throughout the marketing season.

The Idaho® potato grower, along with technology developed over the years by the University of Idaho, has learned to create the ideal environment to keep the tubers in fresh, firm physical condition and to preserve the flavor and texture for long periods. The two most important factors are temperature and humidity.

In the early days of potato cultivation in Idaho, potatoes were stored in “pits” or cellars. The greater part of the interior space of these homemade facilities was underground—a long, wide trench dug in the earth. Most often, the roof, which started at the ground level, was supported by rafters made from peeled logs. This structure was covered with wire netting to support a thick layer of straw, which served as insulation. Soil was spread over the straw to complete the roof structure.

The only real walls that had to be built were the ends of the buildings, which had large doors to accommodate trucks for loading and unloading. Control of temperature in these cellars was difficult, and control of humidity was completely absent. The potatoes were simply piled from the earth floors to the rafters, and buildings closed up to keep cold air out. Rudimentary as they were, these storage pits held potatoes reasonably well until early spring.

Idaho shippers were constantly receiving requests from customers who wanted them to supply fresh Idaho® potatoes in the “off” season. And, as the processing industry developed, the processors found that they needed to operate their plants on a year-round basis. Research on storage was accelerated, and it paid off handsomely.

Researchers found that the ideal storage temperature for commercial potatoes was 42–45°F and that relative humidity should be kept at 95 percent. They also found that an air circulation system enabled the storage facility to blow air up through the huge piles of potatoes in storage buildings, which made it possible to control these vital environmental conditions.

Careful handling and storage are also required at the warehouse level. Potatoes should be stored and handled in a cool (42-50°F) environment. Every effort is made to minimize light throughout the entire warehousing process.

The two most important factors to keep tubers in fresh, firm physical condition are temperature and humidity.

At first, ventilation systems mixed outside air with air from inside the storage building to get the correct temperature. This worked until summer arrived. When refrigeration was added, growers could keep potatoes as long as 12 months while maintaining quality acceptable to both fresh-market customers and processors. Humidifiers were also introduced to keep the water vapor content of the air high and provide the last needed measure of control.

While very few “dirt cellars” still exist in Idaho, today’s typical potato storage is a metal building of immense size. Some are large enough to cover a football field. The potatoes are still bulk-piled on the floor, which is often now concrete. When the potatoes go into storage, perforated pipes are buried under the piles and connected to large air plenums in the walls or under the floor. The buildings are heavily insulated, and sophisticated control systems turn the air circulation, refrigeration and humidifiers on and off automatically to optimize environmental storage conditions.

Although current storage technology makes it possible to keep the crop for a full year, only the portion that is packed or processed last need be held for the maximum time. Storage buildings are opened up and emptied throughout the marketing season as the potatoes are needed; thanks to modern techniques, the quality remains excellent.