One of the delights of summer in the midwest is fresh sweet corn. Unfortunately, the ears of standard sweet corn varieties (su) retain their quality for only 1 or 2 days in the garden as the sugar is quickly converted to starch. Additionally, standard sweet corn varieties don't store well once harvested.
Sweet corn breeders have overcome these shortcomings by developing high sugar varieties, such as sugary enhanced (se) and shrunken-2 (sh2) types, by modifying genes or altering gene combinations. Both types are sweeter than the standard sweet corn varieties. They may also be harvested and stored over longer time periods as they are slower to convert sugar to starch.
The common name of the shrunken-2 (sh2) varieties is derived from the shrunken or wrinkled appearance of the dried kernels. The sh2 varieties are also referred to as super sweets. While the high sugar content and prolonged harvest and storage periods are highly desirable traits, the sh2 types do have some minor drawbacks. Yields of the super sweet types are generally lower than the standard sweet corn varieties. Poor germination often results when sh2 types are planted in early spring. Standard sweet corn varieties may be planted in late April in central Iowa. The sh2 varieties, however, should not be planted until mid-May. The seeds of sh2 varieties germinate poorly when soil temperatures are below 65ûF and in dry soils. Plant seeds of sh2 varieties in warm, moist soils for best results. If necessary, water after planting to keep the soil moist and promote germination.
Also, the sh2 types must be isolated from sugary enhanced, standard sweet corn, popcorn, and field corn. Cross-pollination between the sh2 types and the sugary enhanced and standard varieties will destroy the quality of both. The kernels will be tough and starchy. Pollen from field and popcorn will produce similar results. Isolation may be achieved by planting sh2 types at least 250 feet from other types of corn and by avoiding prevailing winds. Cross-pollination may also be avoided by planting the various types so they mature at different times. There should be a minimum 14 day difference between silking/tasseling dates.
Suggested sh2 varieties for home gardens in Iowa include 'Candy Store' (bicolor), 'Challenger' (yellow), 'Confection' (bicolor), 'Honey 'n Pearl' (bicolor), 'How Sweet It Is' (white), 'Illini Gold' (yellow), 'Northern Xtra Sweet' (yellow), and 'Phenomenal' (bicolor).
The sugary enhanced (se) varieties produce ears with sweet, tender kernels. The soft kernel pericarps make the corn tender and easier to chew. The harvest and storage periods of se types are slightly longer than the standard sweet corn varieties. They also have a higher sugar content. (The sh2 varieties possess the longest harvest and storage periods and have the highest sugar content.) Seeds of sugary enhanced varieties possess greater vigor and germinate more readily than sh2 types. It's generally recommended that se varieties be planted 1 week later than standard sweet corn varieties.
Sugary enhanced varieties should be isolated from field and popcorn. Isolation from standard sweet corn varieties is encouraged although not necessary.
Suggested se varieties include 'Bodacious' (yellow), 'Incredible' (yellow), 'Legend' (yellow), 'Precious Gem' (bicolor), and 'Silver Choice' (white).
This article originally appeared in the May 10, 1998 issue, p. 38.
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