MORE than 7,000 years ago the Indians of Mexico began taming and selectively breeding a wild grass called teosinte, which produced a handful of edible grain kernels. They did this so effectively that over millenniums they converted a strawlike stem, producing perhaps half a dozen kernels, into the thick cob and tightly packed rows of modern-day corn, or maize, as it is more widely known. What the Indians began, modern-day agriculturists have continued ever since. The latest advance comes in the form of a new sweet corn, How Sweet It Is, considered improved enough over the many other good sweet corns to win an All-America Selections award this year.
At the same time the National Garden Bureau, an educational arm of the American seed industry, has seen fit to make 1986 the Year of the Corn (food crop) as well as the Year of the Sunflower.
How Sweet It Is is one of the new high-sugar corns that retain their sweetness for many days after picking. In other words, you can pick your corn today and still find it agreeably sweet even if you don't cook it for a week. That was something the old sweet corn varieties could never do. They were noticeably less sweet the day after picking and had lost almost all their sweetness within three days. But many of the new supersweets had their problems, too. They had durable sweetness all right, but somewhere along the road to becoming supersweet, they lost that genuine corn flavor.
The new award winner overcomes this problem. All-America Selections growers give it high marks both for flavor and sweetness. When the AAS gardens at Pennsylvania State University held its open house, I found How Sweet It Is so delectable that I ate a couple ears raw, straight from the stalk.
Corn has proved to be one of this world's more climatically adaptable plants. From Central America the Indians took corn both north and south. After Columbus returned to Spain with seeds in 1493, it quickly spread around the world, following the trade routes of the early Portuguese navigators. With a few exceptions it seemed to adapt to whatever climate it was taken to.
Colonists in this country were introduced to many varieties of corn by the Indians. In 1779 the first recorded sweet corn was collected from the Iroquois. In 1821 a Connecticut seed company listed what it called sugar corn in its catalog for the first time. Much of the early selection and breeding of sweet corns was done in New England; in 1924 the Connecticut Agricultural Experiment Station introduced the first hybrid sweet corn -- Red Green.
We eat processed field corn as breakfast cereals, grits, corn muffins and breads, chips, and margarine. But for most of this century we have turned exclusively to the sweet variety when eating freshly picked corn.
Fortunately corn, sweet or otherwise, is one of the easier crops to grow, given adequate space and plenty of sun. For tiny gardens there's even a dwarf variety, Golden Midget, so compact that it can be grown in pots on the patio. It produces four-inch ears on stalks less than three feet tall. I've grown them myself, and the flavor is good.
Average garden soil will support sweet corn, but the richer the soil the better the harvest. Really good soil will yield two good-sized cobs a plant. The ideal is to grow a green cover crop in the fall, till this in in the spring, and then turn in compost or manure to a depth of 12 inches. With little or no compost add a pound of 10-10-10 commercial fertilizer or bonemeal for each 25 feet of row.
Most corn does well when planted out directly in soil that has warmed to about 60 degrees F. or more. On the other hand horticultural researcher David Tresemer of Brattleboro, Vt., gets great results with 12-inch transplants that he starts indoors in two-inch soil blocks.
Sow the seed 1 inch deep, 4 to 6 inches apart, in rows 30 inches apart. Have at least 4 rows to produce the block effect so important for good pollination of corn. When the seedlings are 4 inches tall, thin to 12 to 15 inches apart.
Another option, where space is limited, is to grow four plants wherever you have a spare square foot of soil. Plant one seed at each corner of the square foot. You may want to plant extra seeds to allow for less-than-perfect germination; you can always thin later.