The Search for Sweeter Corn

Published: June 1, 2010

Few culinary experiences can match the pleasure of eating freshly picked, home grown sweet corn. The term “freshly picked” is used since sweet corn connoisseurs know that the greater the delay between harvest and consumption the less sweet will be the taste. There is sound science that supports this conclusion. From the moment an ear of sweet corn is harvested, the sugar it contains in its kernels starts to change into starch. Therefore, sweet corn picked afar, shipped great distances and allowed to sit on the produce counter of a supermarket for a number of days cannot begin to match the table quality of freshly picked. People who have not had the pleasure of tasting “fresh” sweet corn do not know how good it can be.

“To make the best better” is the motto of the 4-H youth organization. It also seems to be the ideology of sweet corn breeders since recent advances have made this popular vegetable even more enjoyable to eat. While I certainly respect gardeners who have a preference for heirloom vegetables, in the case of sweet corn they don’t know what they are missing.

Sweet corn (Zea mays var. saccharata) is a mutant strain of corn (or maize) that accumulates about twice the amount of sugar in its endosperm (storage tissue) than does dent (field) corn. Maize is believed to have originated in Central America and was a staple food of Native Americans for centuries. Interestingly, sweet corn was not. Either its taste was not to the liking of Native Americans or they found it difficult to perpetuate it by preserving seed from year-to-year. The first mention of a sweet corn variety was not made until 1779. Today there are over 200 varieties available to the gardening public.

Early varieties of sweet corn were sweet because of the action of a sugarinducing gene (su) located on a particular chromosome in its genome. Several new mutants have been identified in recent years that improve upon the desirable effects of the su gene. These include the se (sugary enhanced) and sh2 (super sweet) genes.

The se varieties of sweet corn, also referred to as Everlasting Heritage (EH), contain considerably more sugar than do the su varieties. Therefore, they remain sweet several days longer after harvest. Sugar is still converted to starch once the corn is removed from the plant but, since there was more sugar to begin with, more sugar remains several days later. Consumed immediately after being harvested, the se varieties are an eating experience almost too delightful to describe.

The sh2 varieties of sweet corn have several advantages over the previous two types. In addition to being three times sweeter than su sweet corn, the conversion of sugar to starch in varieties carrying the sh2 gene is negligible. Thus sh2 varieties start sweeter and stay sweeter than normal (su) sweet corn. Since the endosperm of seed results from the genetic influence of both parents, sh2 (and se) varieties must be prevented from cross-pollinating with other varieties. This can be accomplished by staggering planting dates by at least 14 days or separating plantings by a distance of 250 feet or more. Unfortunately, the germination of seed containing the sh2 gene is more difficult than the other types.

Synergistic hybrids (hse or SY) represent the newest type of sweet corn. This group of sweet corn varieties have about 75 percent of their kernels as sugary enhanced (se) sweet corn and 25 percent as super sweet (sh2). Synergistic types have higher sugar content than regular se types and have excellent shelf life and kernel texture.

Table 1 lists some of the newer sweet corn varieties along with their genetic make-up for sugar induction.

Sweet corn is a heat-loving plant that requires at least eight hours of direct sun to thrive. Normal (su) and sugary enhanced (se) varieties should not be planted until (or slightly before) the average frost free date for a given area because of sweet corns dislike of cold temperatures. Because of their poor germination tendencies and the lack of early vigor, super sweet (sh2) varieties should not be planted until soil temperatures have reached 60o F. Seed should be planted approximately one inch deep in rows spaced between 30 and 42 inches apart, depending upon equipment used. Thin to a density of one plant every 8 to 10 inches within the row after seedlings emerge. Since sweet corn is wind-pollinated it should be planted in blocks.

Sweet corn prefers a well-drained soil that is slightly acidic (pH 5.5-6.5). It has a high nitrogen requirement and a preplant application of a balanced fertilizer containing nitrogen (e.g. 10-10-10) at the rate of about 2-3 pounds per 100 square feet should be made when preparing the seed bed for planting. An additional side dressing of nitrogen at tasseling also is advisable, especially in lighter, sandy soils. Adequate water is extremely important for good yield of high quality. Soil should not be allowed to drop below 60 percent of field capacity before additional water is supplied. Adequate moisture is especially critical at bloom (silking) time and when the kernels are filling on the cob. Weeds compete with sweet corn for both water and nutrients and should be controlled. Shallow tilling is an effective way to accomplish this objective or, herbicides labeled for use on sweet corn may be applied.

There are relatively few diseases (e.g. smut and rust) that plague sweet corn but numerous insects that do. Corn earworms, cutworms, army worms, wire-worms and root worms are the most problematic. Damage from the soil-borne worms can be lessened through proper garden sanitation (fall clean-up) and avoiding planting sweet corn in ground that was not clean-tilled the previous year. Carbaryl (Sevin) is popular for corn earworm control in the home garden; permethrin, esfenvalerate and spinosad also carry labels for that usage.

Sweet corn normally matures to an edible stage about 22 to 24 days after silking. Warm temperatures along with adequate soil moisture tend to hasten maturity and cool weather and/or dry soil will delay it. Sweet corn usually is considered mature enough to eat when the silks have turned brown and the tips of the ears become blunt. The latter suggests the kernels have filled all the way to the end of the ear. At his stage, kernels of corn squeezed should emit a milky liquid. If immature the liquid would be watery; if overly mature the liquid would be more creamy or doughy.