A   B O U N T I F U L   G A R D E N

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Summer corn: A Tempting Tradition

by Linda Trujillo,
Master Gardener

BOTANICAL NAME
Zea mays

COMMON NAMES
Maize, corn, elote

ORIGIN, HISTORY AND FOLKLORE
Corn is native to the Americas. It is descended from teosinte, a wild grass that continues to thrive in parts of Mexico, Guatemala and Honduras. Archaeologists have found 7,000-year-old evidence of teosinte in dry cave deposits in the Tehuacan Valley of central Mexico.

More than 5,000 years ago, prehistoric people were selectively cultivating maize, along with other plants native to the region (i.e., squash, beans, gourds, chili peppers, avocados, and amaranth).

By the time Columbus arrived in the New World, maize was grown throughout the Caribbean and Americas, from southern Canada to the Andes of Peru.

The horticultural expertise of indigenous people has given us varieties that thrive in the "long day, short growing season" of the northern latitudes, as well as the hot and humid tropics. Other varieties flourish in cold growing climates with temperatures of 40 degrees or at elevations ranging from sea level to 12,000 feet.

Varieties grown by the Hopi and Navajo have the ability to emerge from a planting depth of up to 18 inches. This is truly amazing since most varieties fail to emerge if planted deeper than 3 or 4 inches.

An 1828 seed catalog listed one variety of "modern" sweet corn. By 1881, gardeners could choose from 16 varieties. Today, there are hundreds.


DESCRIPTION
Corn is a member of the Poaceae (Gramineae) family, which includes most grains and grasses. It is an annual and one of the most easily identified plants in any home garden or farmer's field.

Corn has an upright growth habit that can reach 15 feet in height. It is a monocot, which means it has vascular bundles scattered throughout the green stem. Plants may also produce secondary or side shoots that form at ground level or near base of the main stalk.

The dark green leaves exhibit parallel venation and grow to be 2 to 4 inches wide and 2 to 3 feet long.

The roots are that of a grass: a network of shallow, easily damaged roots that can spread a foot or more outward from the main stalk. To improve stability, plants may produce sturdy support roots.

Pollen is produced by specialized male flowers that form in terminal plumes, commonly called tassels. The female flowers, which are found on the lower leaf axils, consist primarily of two parts: the ear and a group of strands, called silks. One pollinated silk produces one kernel.

The fruit (kernels) are large, starchy grains on a thick and sturdy axis (cob). Depending on the variety, cobs may have 8 to 24 rows, with kernels appearing in straight lines or random patterns. Corn comes in a rainbow of colors, from white to red and blue to black.

Corn types are based on the shape of kernel. The most common are Flour, Flint, Flour/Flint, Dent, Sweet and Popcorn.

The Flour types tend to be soft grinding varieties typically used for cornmeal and hominy. The Flint types, which have hard pericarps, are difficult to grind when dry, but offer a greater resistance to insect damage and, therefore, have a longer storage life. The Flour/Flint types have kernels that are hard on the outside and soft on the inside.

Dent types have a dent on the crown of each kernel and are usually grown for animal feed. Sweet types are grown for fresh eating since they are better at producing and holding sugar in the kernels.

Popcorn is a type of flint with colorful, small kernels that burst open when exposed to heat. There are two major kinds: pearl (smooth with rounded crowns), and rice (pointed crowns).

HOW TO GROW
Corn requires full sun, adequate water and benefits from rich, well-drained soil with a pH of 5.8 to 6.5. In the low desert southwest, corn can be planted in early spring (February/March) and late summer (July/August).

Those who prefer the conventional method for growing corn should sow seeds 1 to 2 inches deep in rows spaced 3 to 4 feet apart. Seed spacing depends on the chosen variety and the preferred practice of the gardener. Some gardeners sow 1 to 3 seeds in clusters spaced 12 to 18 inches apart. Others sow 1 to 2 seeds every 3 to 4 inches and thin until they achieve the desired spacing.

Because corn pollen is distributed by wind, better results are achieved when plants are arranged in blocks or spirals with at least 4 plants in all directions.

Corn is a heavy feeder. Once plants reach 6 inches tall, they benefit from regular side dressing with nitrogen rich fertilizer. At a minimum plants should be fertilized 3 times: when knee high, when waist high, and when tassels and silks appear.

Most of the literature available today focuses on growing sweet corn by conventional methods. However, I prefer corn circles, a more traditional method closely associated with the Hopi and Navajo people.

A corn circle is a round basin with a raised ridge around it. The corn circles I use are typically 2 to 3 feet in diameter, 4 to 5 inches deep and spaced 4 to 5 feet apart.

Corn circles allow water to be captured or applied and directed downward toward the roots. In addition, when seeds are sown in a spiral, the outer ring of plants creates a protective wall around plants in the center of the circle. Regardless of wind direction, pollen is carried into the center of the circle where it is more likely to land on exposed silks.

I love to grow native, desert-adapted or heirloom varieties. My current favorite is "Stowell's," which does well when planted in corn circles. I sow 12 to 15 seeds in a spiral pattern 6 to 8 inches apart and 2 to 3 inches deep.

I use the traditional companion planting technique of "Three Sisters." Between corn circles, I plant beans or black-eyed peas and squash. The corn provides afternoon shade, as well as support for the beans or peas. The beans or peas increase the amount of nitrogen available to the corn and squash, which reduces the need for side dressing. The squash plants weave their way around the stalks and their large leaves shade the soil, which reduces moisture loss due to evaporation.

Whether you prefer growing corn by a conventional or traditional method, when temperatures soar above 90 degrees, it may be necessary to hand pollinate in the early morning hours to ensure a good harvest.

The method I use is to take a large stainless steel bowl and hold it next to the main stalk just below the tassel. Then tap the tassel so pollen falls into the bowl. Collected pollen is then distributed onto exposed silks.


VARIETIES AND SEED SOURCES
Stowell's is an heirloom variety originally introduced in 1848. The plant grows 8 to 10 feet tall and produces two or more 7- to 9-inch-long ears per plant. These sweet-flavored, white-kenneled ears mature in about 100 days.

I choose Stowell's for fall planting because it "holds" fresh-eating ears longer than other varieties. It is also unique in that should the weather turn unseasonably cold, the plant can be pulled up with immature ears attached and hung upside down in a cool place, such as a garage or storeroom, where the ears will continue to ripen until they can be harvested.

Most local plant nurseries or mail order seed houses offer a wide variety of corn seed. My favorites are Native Seed Search, Seeds of Change and Botanical Interest. Limited selections by Seeds of Change and Botanical Interest can be found locally at Whole Foods.

PESTS AND DISEASES
Insect pests include the corn earworm, Southwestern corn borer, corn seed maggot, flea beetle, Japanese beetle, and corn sap beetle. Other pests include birds and raccoons.

Diseases include Stewart's wilt, stunt and smut. Smut is said to taste similar to mushrooms and is considered a delicacy in many parts of the world, including Mexico.

WHEN TO HARVEST AND HOW TO STORE
Look at the silks, which darken and dry as the ears mature. Squeeze and feel the ear through the husk to check for kernel plumpness. If an ear looks and feels ripe, then gently pull back the husk to expose a small portion of the ear. Press your thumbnail into a kernel crown to see if squirts out a milky, sweet liquid. If the fluid is clear the ear is not yet ripe, so replace the husk and check again the following day. If the fluid is thick, the ear is still edible but past its prime, so harvest and use as soon as possible.

The method I use to harvest an ear requires both hands. I use one to hold the main stalk above the ear to be harvested. With the other hand I grab and twist the ear, then pull down and away from the stalk.

For short-term storage, leave ears in the husks and refrigerate. For longer storage, whole ears can be frozen unhusked and unblanched. Simply place them in the freezer for about 48 hours, then put them in freezer bags and return to the freezer. Janet Banchand Chadwick, in her book The Busy Person's Guide to Preserving Food details other ways to preserve quickly and easily your bountiful corn harvest.

SEED SAVING
According to Susan Ashworth, sweet corn varieties maintain 50 percent germination for 3 years. Flint, dent and popcorns retain high germination rates for 5 to 10 years. If you plan to save seed, please read the section on corn in Susan Ashworth's book Seed to Seed. It is a complex process, and Ashworth provides clear instructions and photographs that detail various methods, including hand pollination and "bagging" of ears and tassels.

NUTRITIONAL VALUE
Corn is a source of vitamins A, B1 and C, as well as phosphorus. Corn is also high in carbohydrates and contains protein and amino acids. In fact, when corn is eaten with beans and squash, the combination of amino acids creates a protein equivalent to that of meat.

References
Ashworth, Suzanne. Seed to Seed. ISBN 0-9613977-7-2 (pp. 188-196).

Chadwick, Janet Bachand. The Busy Person's Guide to Preserving Food: Easy Step-by-Step Instructions for Freezing, Drying, and Canning. ISBN 0-88266-900-1.

Chesman, Andrea. The Vegetarian Grill. ISBN 1-55832-127-6.

Foster, Nelson and Linda S. Cordell. Chilies to Chocolate: Food the Americas Gave the World. ISBN 0-8165-1324-4.

Mikel, Terry H. and Kai Umeda. UofA Cooperative Extension Online Publication, "Growing Sweet Corn in Arizona." www.ag.arizona.edu/pubs/crops/az1141.pdf.

Nyhuis, Jane. Desert Harvest: A Guide to Vegetable Gardening in Arid Lands. ISBN 0-918080-84-3.

Illustrations courtesy of Art Today Corn Photography courtesy of Donna Atwood


Maricopa County Master Gardener Volunteer Information
Last Updated May 28, 2003
Author: Lucy K. Bradley, Extension Agent Urban Horticulture, University of Arizona Cooperative Extension, Maricopa County
© 1997 The University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension in Maricopa County
Comments to Maricopa-hort@ag.arizona.edu 4341 E. Broadway Road, Phoenix, AZ 85040,
Voice: (602) 470-8086 ext. 301, Fax (602) 470-8092