Sweet Corn: A Summertime Treat

Summer brings with it many pleasures not the least of which is the highly anticipated arrival of the first home-grown sweet corn of the year. I come from a family which takes sweet corn very seriously. First, it is a source of great family pride to have home-grown sweet corn available on or before the 4th of July; failure to do so would be a source of public embarrassment. Secondly, the preparation itself of sweet corn for consumption is quite a ritual and must be preformed to exacting specifications. Just prior to mealtime, a large pot of water is brought to a slow boil on the stove. This accomplished, the family member gifted with the ability to judge when sweet corn is at its most succulent stage of maturity goes to the sweet corn patch (located strategically close to the kitchen) to gather the meal. Once the sweet corn has been picked, this person walks briskly toward the kitchen cleaning the sweet corn in full stride along the way. The corn is then gently lowered into the boiling water where it is allowed to cook. The objective is to permit as little time as possible to pass from the moment the ears of corn leave the mother stalk until the first mouthful of this delicacy is consumed.

Although the preceding might sound a bit extreme, there is a "method to the madness" in the ritual described for those who take sweet corn seriously. From the moment an ear of sweet corn is harvested, the sugar it contains in its kernels start to change into starch. Therefore, the more time that elapses between harvest and consumption, the less sweet flavor the corn will have. This largely the reason why people who have not had the pleasure of tasting "fresh" sweet corn do not know how good it can really be.

Sweet corn (Zea mays var. saccharata) is a mutant strain of corn that accumulates about twice the amount of sugar in its endosperm (storage tissue) than does field, or dent, corn. The origin of corn is uncertain and believed to be very complex. It is speculated that corn, more appropriately called maize, is native to the Andean region now occupied by southern Peru and arose from the chance cross between two species of wild grass. This inter-specific cross was thought to have mutated to produce "pod corn" in which each kernel was enclosed by its own husk. Pod corn later mutated to a form in which husks around individual kernels was absent. Native Americans carried this form of maize to Central America where it hybridized with a related species called Tripsacum and took on the common name "teosinte". Teosinte, a hybrid with maize as one of its parents, is thought to have back-crossed with maize to form our modern-day corn types. Although maize was a staple food of Native Americans for centuries, 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 sugar-inducing gene (su) located at a particular locus in its hereditary makeup. Several new mutants have been identified in recent years that improve upon the desirable effects of the su gene. These include the sugary enhanced (se) and shrunken-2 (sh2) 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 there will be more remaining several days later. Consumed immediately after being harvested, the se varieties have been by sweet corn fans as a eating experience almost too delightful to describe.

The sh2 varieties of sweet corn (also called super sweet) has several advantages over the other two. In addition to being three times sweeter than normal corn, the conversion of sugar to starch in varieties carrying the sh2 gene is negligible. Thus super sweet varieties start sweeter and stay sweeter than normal sweet corn. Since the endosperm of seed results from the genetic influence of both parents, super sweet varieties must be prevented from cross-pollinating with non-super sweet 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) represent yet another type of sweet corn. These hybrids combine the beneficial traits of the se and sh2 genes into one variety. The following table lists some of the newer sweet corn varieties along with their genetic make-up for sugar induction.

Variety/(gene)	Maturity	Color	Comments
Bodacious (se)	75 days	yellow	High yielding; good seedling vigor
Frisky (hse)	69	bi-color	Early with great flavor; excellent early vigor
Gold Nugget (se)	75	yellow	Superior holding ability; gaining popularity
Jackpot (se)	80	bi-color	Excellent quality; good disease tolerance
Incredible (se)	85	yellow	Leading market-garden variety; great flavor
Peaches and Cream (hse)	85	bi-color	Excellent flavor; tender kernels
Silver King (se)	85	white	Sweeter version of the popular Silver Queen
Sugar Baby (se)	65	bi-color	Very early; tolerant of cool soil; very sweet
Tender Treat (hse)	95	yellow	Slow conversion starch to sugar; tall stalks

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 60 degrees. 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 eight 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 pre-plant application of a balanced fertilizer containing nitrogen (e.g., 10-10-10) at the rate of about two to three 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 apply herbicides labeled for use on sweet corn.

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. As previously mentioned, sweet corn quickly loses quality after it is harvested and should be consumed or preserved as soon as possible after it is picked.

David Trinklein Horticulture
573-882-9631