2000: Year of the Sweet Corn

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Sweet Corn Black Aztec and a sweet yellow corn

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Ornamental corn, Black Azetc, sweet corn and popcorn

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2000: Year of the Sweet Corn

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2000: Year of the Sweet Corn

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2000: Year of the Sweet Corn

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2000: Year of the Sweet Corn

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2000: Year of the Sweet Corn

Sweet Corn is an indisputable native of the Americas and has been consumed for 7,000 years.

2000: Year of the Sweet Corn

Sweet Corn is an indisputable native of the Americas and has been consumed for 7,000 years. Because of its New World origins, history, popularity and adaptability, the National Garden Bureau celebrates the new millennium as 'The Year of the Sweet Corn.'

The fact sheet contains the origins of corn, a.k.a. maize, the breeding and development of recent cultivars, cultural practices and harvesting help for all gardeners in North America.

History

The National Garden Bureau found the origin of corn or maize to be in Mexico. A wild grass, Teosinte (Zea Mexicana) is the ancestor of all known species. Teosinte grows wild in remote areas of Mexico and Guatemala. The oldest known remains of corn were discovered in Mexico's Valley of Tehuacan, and dated at 7,000 years old. The earliest corn cob found was from 5,000 B.C. and was unmistakable. The cob was enclosed in a husk-like casing. This husk means the corn was dependent upon man to open and disperse the kernels. So, the oldest cob on record was dependent upon man for its survival. Corn spread from its center of origin, Mexico, north to the U.S., and south to Central and South America. Almost 300 diverse forms of corn have been described from these regions. Corn has proven to be one of the most climatically adaptable members of the grass family.

The ancestral source of sweet corn is an Andean corn, Chullpi. This corn contains the sugary gene and produces an ovid shaped ear bearing 18 to 30 rows of yellow kernels. In prehistoric times, Chullpi was not boiled or roasted but dried and eaten as sweet snacks. Also, the high sugar content made a higher alcoholic content drink, popular in Bolivia and drunk with the Chullpi snacks. In northern Peru, a well preserved ear of this type was dated at between 1,000 to 1,534 A.D.

In the United States, sweet corn remains have been found in New Mexico and northern Arizona caves and date from 1,200 to 1,300 A.D. The native American Indians grew maize, which is the broad category of all corn types. Native Americans were probably the first breeders of corn selecting the best plants and saving seed from season to season. By the time Columbus discovered America there were hundreds of forms or types of maize (corn).

Columbus is attributed with bringing maize back to Spain on his return voyage in 1493. Its cultivation spread quickly following the trade routes of Portuguese in the early 1500's. One account has maize reaching the Philippine Isles from the west before Magellan arrived from the east in 1521.

The Native Americans had been cultivating flint (or field) corn, sharing many different kinds with the colonists. In 1779 the first recorded sweet corn was collected from the Iroquois Indians of the Susquehanna River Basin. The variety, Papoon, was the first colonial sweet corn to be established in New England. In 1821, a Connecticut seed company listed sugar corn in their catalog, the first seed source for home garden sweet corn. The early American gardeners preferred white kernel corn to yellow, possibly because Papoon was white.

Sweet Corn was an American favorite food even as early as the 1880's. James Vick's Flower and Vegetable Garden book published in 1880 listed many sweet corn varieties for gardeners. He wrote, " the earliest good sweet corn we are acquainted with is the 'Minnesota'." He also described 'Stowell's Evergreen' as :"Magnificent late variety, keeping in eating until frost, almost." 'Stowell's Evergreen' was introduced in 1853. Looking in seed catalogs, a gardener may find seed available of some of these old time varieties such as 'Country Gentleman' introduced in 1890. Both of these popular sweet corn varieties are white kernel corns. It seems the popularity of white corn changed in 1902 with the introduction of 'Golden Bantam.' This W. Atlee Burpee Company introduction became a household name and changed the preference from white to yellow kernel corn.

When the Mendelian laws were generally recognized about 100 years ago, the development of hybrids began. Many hybrid experiments were conducted in New England on sweet corn. The first hybrid sweet corn, 'Redgreen' was released by the Connecticut Agricultural Experimental program in 1924. One of the first significant hybrids was 'Golden Cross Bantam' released by Purdue University in 1932. This variety was productive and adaptable to many growing areas in North America resulting in its commercial success.

Nomenclature

Sweet corn, table corn, or sugar corn, is one of the sweetest, most flavorful vegetables grown in any garden. Scientifically, sweet corn is called Zea mays rugosa. It is a cultivar of field corn (Zea mays L.). The genus Zea, is Greek for some cereal. It is the species mays, a different spelling for maize which means corn, and the variety regosa, means wrinkled and refers to the mature seed. Corn is a member of the grass family Gramineae.

Pollination

Corn is monoecious, having male flowers on top of the plant and female flowers (silks) at leaf axis along the main stem. The male flower, called the tassel, can produce up to a million pollen grains. The pollen begins to shed several days before the female silks emerge, but continues to produce pollen and mature for many days. Pollen moves by wind and gravity. It is for this reason that single rows of corn don't usually pollinate and yield as well as many rows side-by-side. The ear, or female flower, is enclosed in several layers of "husk" with only the fine string-like styles or silks emerging above for pollination. The ovaries are produced in rows along the upright axis of the spike or cob. After fertilization they develop into kernels.

Corn Categories

There are six major categories of corn. As gardeners, we are most interested in Zea mays regosa, sweet corn. Gardeners can grow popcorn, the type of corn that explodes when heated. Genetic dwarf or midget corn is a unique type with mature ears at 4 to 6 inches in length. A decorative corn called broom corn, is grown for the long fibrous tassels that can be dried for arrangements. The principal commercial corn is called dent due to the hollow space on the top of dried kernels. Dent corn is primarily used for domestic animal consumption. Lastly the sixth category is the decorative multicolored Flint or Indian corn having the hardest kernels when dried. Corn remains one of the world's three most important cereal crops for human and domestic animal consumption.

Ornamental and Popping Corn

The genetic diversity of corn is most evident in the ornamental or Indian corn. Kernel colors range from mahogany, red, yellow and orange to deep blue. Combinations of these colors occur on one ear. Rainbow, Squaw, or Indian corn varieties are the most popular and can be harvested in 110 days. Just pull back the husks and allow them to dry. These ornamental types with their calico colors are used indoors or outside for Halloween or Thanksgiving decorations. There are also miniature types with 2 to 4 inch multicolor ears.

Popcorn can be grown and used as decorations or as a healthy snack food. The strawberry popcorn is one of the most decorative with its red kernels and short, blunt shaped ears. Popcorn is available in yellow, white, red and glossy black kernels. High-yielding hybrids often bear 2 or 3 ears per stalk. The harvested popcorn ears need to be cured before popping. Place ears in a mesh bag or open woven basket and store in an airy, warm, dry location (attic, garage) for three to four weeks. This allows the outer shell of the kernels to harden. Shell when kernels drop from cob with a moderately aggressive twisting motion from both hands or rub two cobs together. Store kernels in clean jars with airtight lids.

Black Aztec corn is one of the oldest types grown and still in commerce. It is described as being identical to the corn that Aztec farmers grew 2,000 years ago. Ears are white in the young milk stage and sweet when cooked. If ears are allowed to dry, the kernels turn jet black. When ground, the dry kernels make a blue corn meal for either baking or cooking.

Corn - From Sweet to Sweeter

There are three types of sweet corn. They are normal sugary (su), sugary enhanced (se) and supersweet (sh2). These types refer to the sugar content and sweet flavor in the kernels when mature. The normal sugary (su) sweet corn will convert kernel sugar to starch immediately after harvest. This means the sweet flavor is rapidly lost. The supersweet or "shrunken two" (sh2) type was discovered in 1950 by Dr. J. R. Laugham, University of Illinois using traditional breeding techniques. He discovered a corn containing more sugar and when dried, the kernels shrunk thus the name shrunken. These high sugar types were named Supersweet because the sugar content can be twice as great as normal sugary (su) sweet corn at peak maturity. The Supersweet types slow down the conversion of sugar to starch so that the sweet flavor lasts longer after harvest.

About ten years later, again at the University of Illinois, Dr. A.M. Rhodes bred a corn with sweet flavor and tender texture. Dr. Rhodes called this new type, sugary enhanced (se) genetic types. The (se) corn has higher sugar levels and because of this, the sweet flavor will last longer after harvest. Overall (se) sugary enhanced types have increased in popularity because they combine the sweet flavor with ease of growing for gardeners.

For the new millennium, there are hybrids that combine two or three types of sweet corn. One variety can offer gardeners a combination of sugary enhanced (se) and supersweet (sh2) or all three types, adding normal sugary (su) to the hybrid. The advantages to the gardener are the higher sugar levels provide a sweet flavor but with the ease of growing normal sugary (su) types. Fresh sweet corn of these synergistic hybrids are mouth watering sweet and not as "crunchy" as older supersweet (sh2) types.

Gardeners can expect sweet corn improvements through traditional breeding techniques such as earliness, flavor and new kernel colors. For 2000, there is an AAS Vegetable Award Winner, 'Indian Summer', a (sh2) supersweet with multicolored kernels. The kernels can be yellow, white, red or purple.

Culture

Gardeners can grow white, yellow, bicolor or multicolored kernel corn. Provided a gardener has sufficient space, an early (65 to 70 days), mid-season (75 to 85 days) and late season (85 to 100 days) variety could be grown to have a constant harvest of fresh sweet corn. There are hundreds of sweet corn varieties from which to choose the ones to grow in your garden.

There are just a few simple rules to follow to grow a bumper crop of sweet corn. Site selection, soil nutrients and water are very important to grow a bounty of fresh corn on the cob. To begin, select a site on the north side of your garden. Corn plants are tall so that if planted on the east or west side, they will cast shadows on the other garden plants and decrease plant production. All vegetable plants need maximum sunlight.

There are two basic ways to plant sweet corn, in blocks or in hills. If space is not a problem, plant rows of corn in blocks of a minimum four rows, 2-½ to 3 feet apart. This is termed "block" planting; the rows can be as long as the gardener wants. For adequate pollination, sow all corn seed at the same planting. An alternative is to sow the corn in double rows in raised beds. If your soil is very poor, raised beds will be easier to establish, improve and maintain.

For small plantings of sweet corn, sowing in "hills" is sometimes recommended. Hills are groups of 4 to 5 seeds sown in a circle, with 2 inches between seeds. Space the hills 2 to 3 feet apart and when the seedlings are established, thin each hill to 2 to 3 plants. For adequate pollination, a minimum of 12 - 24 plants are required.

Corn can be grown in large tubs (2-3 ft. deep) for a patio container crop. Choose a large and deep container to be able to maintain soil moisture levels. Place container in full sun or on a movable plant coaster to easily transport to sunny location. Sow two or four seeds in clusters, six inches apart. Thin seedlings, choosing most vigorous plants keeping one plant for every six inches in the container. Maintain high nutrient levels and water frequently as soil will probably dry quickly in the container. To insure proper pollination, shake the stalk allowing pollen to fall into the silks. Repeat shaking process for several days while pollen is maturing. Continue watering and fertilizing as ears fill out.

Isolation

The new supersweet (sh2) types of corn are excellent eating, but to ensure their best flavor, the gardener must isolate these types from normal sugary and sugary enhanced sweet corn. The two easiest ways to provide isolation are to grow only one variety of sh2 sweet corn or to grow several varieties which have different maturity dates of at least 10 -14 days from the supersweet, so that they will not be releasing pollen at the same time.

Prepare Garden Soil

While average soil will support sweet corn, the better it is amended and prepared, the better the yield. Some recommend planting a green manure in the fall to till under in the spring; then incorporating compost or manure to a depth of 12 inches. Or, add one pound of 5-10-10 or 10-10-10 fertilizer, bonemeal, or wood ash per 25 foot row. In most areas sweet corn seed does best when sown directly into the garden soil. If the soil is adequately warmed the seeds germinate relatively quickly. At temperatures of 58 to 68 degrees F, germination takes 7 to 12 days; soil temperatures of 77 to 95 degrees F, germination will take just 4 to 5 days. Some gardeners sow early-, mid-, and late-season varieties at one time. Because of their different maturity dates, harvests will be naturally staggered.

Sowing Seed

Sow the seeds 1¼ inch deep and four to six inches apart. Most supersweet varieties will not germinate well in cool soils. Soil temperatures should be at least 65 - 70º F to achieve optimum germination. When the seedlings are 4 inches tall, thin them to 8 to 10 inches apart. Be uncompromising when thinning, if left too close, yields will be reduced. In areas with very short growing seasons it may be advantageous to sow the seeds in peat pots, indoors, 4 weeks before the last expected frost. Then transplant the entire pot into the garden after the soil warms.

Successive Sowings

Many gardeners choose to plant sweet corn varieties in successive sowings. One favorite sweet corn variety can be sown two weeks later than the first sowing to extend the harvest of fresh sweet corn. The second sowing will mature about two weeks later than the first. There are two primary benefits from this sowing technique. This extended fresh harvest will allow gardeners a longer time to eat fresh sweet corn or allow time to freeze or can the later crop. Both are easier than if all the sweet corn is ready to harvest within a short time span.

Growing On

After planting, watering becomes the most important activity for good sweet corn production. When watering, irrigate the soil rather than the whole plant with overhead sprinklers. This will ensure proper pollination. Sweet corn is wind pollinated; the pollen drifts from the tassel to the silk. If the tassels and pollen are wet with water, the pollen won't leave the tassel or will be washed down to the soil hampering any chances for pollination. It is critical to water sweet corn just before the appearance of the silk and a couple of weeks after the silks turn brown. This constitutes the kernel filling state. During a drought, irrigation every 10 to 14 days will sustain the plants.

Deep watering is always better than shallow for all soils except sandy types. Sweet corn matures in 9 to 15 weeks depending on the variety. For optimum growth and production, keep the sweet corn rows or hills weeded. Hoeing is recommended until the stalks stand 12 to 15 inches tall. As they grow taller avoid deep disturbances around and between the corn stalks as this may damage the shallow root system. Mulching with hay, compost, newspapers or other organic biodegradable materials will help to maintain the moisture and control competitive weeds among corn.

Sweet corn is a heavy feeder and will quickly deplete soil nutrients. Additional fertilizer or compost is needed when stalks are 8 inches tall and again when the tassels appear.

Pests, Diseases, Growing Problems

In most areas corn borers are a problem. Their caterpillar-like larva are first noticed by a small pile of sawdust-like matter beside a small hole on the stalk beneath the tassel. The worm will crawl down and eat its way into the ear if not removed or smashed at the first sighting. Another common pest is the corn earworm. The eggs are laid on the silks, and the larva of a Noctuid moth eats its way into and down through the ear of corn consuming the immature kernels along the way. The damage is usually to the top of the cob. It is sometimes considered more of a nuisance than a menace. Placing a rubber band, or clothespin on the tip of the ear sometimes helps prevent the earworm from entering the ear. Research has shown that the earlier in the season the corn is planted the less severe the earworm damage. Also, corn earworms are less of a problem in areas where the winter temperatures fall below 0 degrees F.

Pests of a Larger Stature

Many gardeners find that raccoons, deer and other wildlife prefer corn over other garden vegetables. To protect the young ears of corn from raccoons, Jim Schuster, University of Illinois Extension Service, suggests sprinkling stalks and leaves with baby powder. Re-apply after each rain to deter the raccoons. To deter both deer and raccoons use Dial soap. "I don't know why they are repelled by Dial, but tests have shown it is the only soap that works," Schuster said. Hang a half bar of Dial soap on 2-½ ft. and 1 ft. stakes, allowing the soap to dangle 6 inches above the ground, otherwise the mice can reach it and will eat the soap. Place the stakes 4 ft. apart, all around the perimeter of the block of corn and intersperse between the rows.

Harvest

The fun begins when the corn comes in. Many long-time gardeners will tell you "don't pick the corn until the cooking water starts to boil." It is true for some varieties but not all. Sweet corn has a very high percentage of sugar and water in the composition of the kernels. When at its prime the kernels will be soft and succulent. As the ear matures the water decreases, the sugar turns to starch and the kernels become tough with a doughy consistency. Most varieties of sweet corn are ready to eat in two and a half to three weeks after pollination. Very hot temperatures will hasten the maturity of the corn in the garden. External clues to determine when to harvest include looking for brown, dry silks and the cob having a round, blunt tip. If the husk fits tight to the cob, the corn is ready; if there seems to be looseness or softness, allow the kernels to fill out for another day or so.

If the ear seems to be mature but you still feel uncertain, do one last test before picking. Carefully pull back part of the husk to expose the kernels. Examine kernels which should be full and plump almost to the tip of the ear. For normal sugary sweet corn a test is to pop one of the kernels with your thumbnail, if the juice spurts out and looks milky, harvest. If the juice is clear, wait another day. This thumbnail rule for milky juice does not apply to the high sugar types. Both supersweet (sh2) and sugary enhanced (se) types are mature when the kernel juice is clear. To remove the ear, pull down and twist.

Storage

After harvest, store corn in the refrigerator to retain the most flavor. Sweet corn can be stored by canning or freezing. The easiest method is freezing. Blanch corn for 8 to 10 minutes, then chill thoroughly in cold water and freeze.

 

This fact sheet was prepared by the National Garden Bureau as a source of information for garden writers to use in celebrating 2000 as the 'Year of the Corn.' The National Garden Bureau acknowledges the experts who reviewed this fact sheet for accuracy. They are George Crookham, Crookham Seed Co.; Mark Willis, Harris Seeds; and Diana Jancik, Novartis Seeds Inc. Special thanks to Tom Eltzroth for the photography and to Johanna McCormick for the fact sheet design.

Please feel free to use the material as is (clip and paste-up) or rewrite to meet your own needs. Each section can be used as a separate article or topic. The entire fact sheet may be reproduced without permission. Please provide a tearsheet to NGB headquarters and please credit the National Garden Bureau.

The National Garden Bureau is a non profit organization and recognizes the seed company members that generously donate funds to publish this fact sheet. For 2001, the Bureau will celebrate the 'Year of the Basil and Centaurea.'