Corn Confidential

By National Gardening Association Editors, June 23, 2008

You watered it, fed it, and nursed your corn crop through the summer. Finally it's time. You pick a few ears and run for the pot of water boiling on the stove. But as you eagerly husk the ears you find them smiling up at you like a hockey player who's played too many games without a mouthguard. If you're really unlucky you find you've got more cob than kernel.

It doesn't seem like too much to ask: one stalk, one perfect ear of corn. Yet many gardeners have trouble making that yield. Corn really isn't made for the home garden. It takes a lot of space, and has a particular style of pollination that causes problems.

If a tomato blossom doesn't get pollinated it won't make a fruit, but others will come along quickly enough. Chances are you'll never even notice that anything is amiss. But for corn, incomplete pollination is obvious. It produces gap-toothed ears and gives a subtle cobby flavor to the corn that isn't quite right.

Corn pollination is a complex process. The pollen forms on the tassel and has to get from there to the female flowers deep within the husk of the emerging ears. The silk is the road it travels. Each silk is connected to a pair of female flowers on the cob. When a female flower is fertilized it forms a seed--a kernel of corn. If a flower is not fertilized it leaves a gap on the cob. That means that hundreds of (maybe even a thousand) fertilizations have to take place to fill out a single ear of corn.

In farm plantings there's so much pollen in the air and so many fields of corn in the vicinity that pollination is inevitable. Even in the smallest corn patch there's plenty of pollen to go around. Each tassel produces millions of microscopic grains of it. The problem, especially in a small garden, is getting it where it belongs. Wind will whisk it away. Rain will hurl it to the ground. Heat will kill it. In temperatures over 90oF pollen grains remain viable for less than 24 hours.

Home garden corn patches suffer from the "edge effect." A long and narrow patch will have lots of plants on the edge, making it more likely that their pollen will blow away. The longer the edge of the patch, the lower the percent of pollination. By planting in blocks instead of long rows, and facing the shortest edge in the direction of the prevailing winds, you increase the likelihood of pollination even more.

Giving Nature a Hand

If you find you're still getting too many skips, you can try a breeder's trick--hand-pollination. Breeders hand-pollinate corn in order to keep strains pure or make crosses. Because they want to prevent natural pollination they have to bag both the ear and the tassels before the silks and pollen come out. They collect the pollen and carefully sprinkle it on the silks of selected stalks, then place the bag back over the ear.

But in the home garden you don't want to prevent wind pollination; you want to augment it. There's no need to stop cross-pollination (unless there's field corn or popcorn coming into tassel at the same time within one mile of your patch). You just want to make sure all the silks get their fair share of pollen.

The trickiest part is choosing the right time. That means keeping an eye on the tassels and ears. After the tassel has emerged and begun to spread open, the scaly spikelets open up and small yellow anthers emerge and begin releasing golden pollen grains, 1/250 of an inch in diameter. You'll want to start pollinating as soon as you see them.

Go out in the morning after the dew has burned off and grab the tassel. Bend it over gently without breaking it and shake it over the emerging ear. Or break off a tassel from a plant in the middle of the patch and shake it over those on the outside. The object is to get a grain of pollen on every silk.

Some corn experts say you'll get better pollination if you first cut the silks back to an even length so they're brushlike and bristly rather than ragged. The tassels will keep manufacturing fresh pollen for about a week, so you can repeat the pollinating daily.

Spacing and Care

In an attempt to reduce the edge effect, you may be tempted to jam a lot of corn into a little space. Don't. If gardeners make one mistake in growing corn, says Bill Watson, president of Liberty Seed Company in New Philadelphia, Ohio, it's planting too close. "They crowd plants into rows or plant three or four seeds in hills 12 inches apart. And they don't get anything," he says.

No amount of fertilizing, watering, or hand-pollinating can rescue corn that's too crowded. Watson says corn needs to be planted in rows three feet apart with seeds 10 to 12 inches apart in the rows. You'll need about four ounces of seed to plant four 25-foot rows, yielding about 100 ears of corn.

David Sperling, director of research at Robson Seeds in Hall, New York, says that if you're growing small, early corn with short stalks you might get away with planting it in blocks, spacing the seeds 12 inches apart in all directions. But make sure the corn patch is no more than four plants wide. The flip side of the edge effect is that corn likes to be at the edge of the field where it will get full sun from the ground up.

If you don't feel you can spare the space to plant single rows three feet apart, you can cheat a little bit, says Sperling, and get more plants per area by planting double rows. Sow two rows about a foot apart, with seeds 10 inches apart in the rows and configured so that the hills are staggered. From the center of that paired row, move over three feet and make that the aisle between two more paired rows. That gives you four rows in four feet instead of four rows in 10 or 12 feet.

Even when planted at the maximum spacing, corn needs plenty of food and water. "You've got to use a starter fertilizer, and then you should sidedress two more times," Watson says. Here's a growers' secret.

Use a fast acting fertilizer, an amount equivalent to two pounds of 6-12-12 per 100 square feet. Then go through and sidedress when the corn is about six inches high and again when it just begins to tassel. Each time just dribble a bit of 6-12-12 along both sides of the row.

You can use organic fertilizers, but since they're usually slow acting you should apply the bulk of it before planting. Try broadcasting cottonseed meal or dried blood at a rate of five pounds per 100 square feet. Then when the corn is about knee-high, sidedress it with a dusting of either.

Make sure the corn is getting at least an inch of water per week. If the soil moisture is depleted the corn will begin to wilt; then it will need about two inches a week as the ears begin to fill out.

Follow these guidelines and you can count on one good-quality ear per stalk. Plant a prolific variety and you may get twice as much.

Breeder's Favorites Revealed

Back in the good old days, you had few decisions to make about which corn variety to choose, because just about everybody planted either'Silver Queen' or 'Seneca Chief'. All you had to decide was which color corn you'd prefer to eat.

The choices are more confusing now. Besides the "normals," which have the normal sugar gene (su) and its variations (su+ and su++ ), we now have sugar-enhanced corn (indicated by the symbols se, SE or EH, depending on its genetic makeup) and supersweet corn, also known as shrunken two corn or sh2. Within these three main categories, there are still other variations (some of the newer supersweets, for example, have both the sh2 and su gene).

Each type has its merits. If sweetness is what you're after, supersweets are the way to go. Thanks to the sh2 gene, these have a very high sugar content, and because they don't convert that sugar to starch, they stay sweet for weeks. But the kernels are less vigorous than other types, requiring soil temperatures of 75oF and plenty of moisture and fertilizer to germinate. And for the home gardener, they can present a space problem, since they must be isolated so they won't cross-pollinate with any other corn (it turns the kernels starchy).

David Wolfe, assistant professor and corn breeder at Cornell University, says, "For the home gardener, the sugar-enhanced varieties are the way to go. They're still plenty sweet but are creamier, giving a better flavor." Most breeders we talked with agreed. "Sugar-enhanced varieties are not sickeningly sweet, have much better cold tolerance, and are more tender than the supersweets, yet still hold their quality," explains John Gale, horticulturist at Stokes Seeds, Inc. There are still plenty of the old standard varieties that are excellent, too. 'Silver Queen' holds its title as the top seller in the South, for instance, and yellow 'Seneca Horizon' is popular throughout the country.

Which type should you grow? There's no easy answer. "Choosing sweet corn is subjective, according to the taste and color you're used to," says Rob Johnston of Johnny's Selected Seeds. Northeastern gardeners, for example, generally opt for the bicolors, those in the West, Northwest, and Midwest stand by the yellows, and white sweet corn is the favorite in the South.

When we talked with breeders to find out which were their top corn varieties, we quickly discovered that everyone has his own favorites. Some are listed below.

Supersweet: 'Honey 'N Pearl' and 'Illinichief';

SE: 'Sugar Buns', Bodacious', 'Miracle', and 'Silverado'

Normal: 'Merit', 'Seneca Horizon', and 'Silver Queen'


Another problem home gardeners face is lodging: plants toppling over in heavy wind and rain. It makes a mess out of the corn patch, but it can also impair pollination and sometimes even pull the roots from the ground. The looser and more tillable your soil is, the worse the problem can be. To prevent lodging, take it easy on the mulch. If you must mulch with an organic matter, wait until late in the season, after the tassels show. You can give the plants added support by hilling them up or planting in a three- to four-inch-deep trench, filling it in as the seedlings emerge.

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