Sweet corn is one of our most popular vegetables. An excellent summer treat, sweet corn may also be canned or frozen for year round use.
Home gardeners can choose from numerous sweet corn varieties. Sweet corn varieties differ in color (yellow, white, bicolor), sugar content, texture, ear size, days to harvest, and other characteristics. There are three basic types of sweet corn. Standard (su), sugar-enhanced (se), and shrunken-2 (sh2) types vary in sugar content, texture, length of the harvest period, keeping quality after harvest, and seed vigor. In recent years, plant breeders have developed synergistic and augmented shrunken-2 types of sweet corn that are combinations of the three basic sweet corn types.
Standard sweet corn varieties have been grown for many years. These varieties possess the traditional sweet corn flavor and texture. (Sweet corn differs from field corn by a single gene called the sugary or su gene.) Unfortunately, the ears of standard sweet corn varieties retain their top quality for only 1 or 2 days. Also, standard varieties don't store well once harvested. Suggested standard sweet corn varieties for home gardens in Iowa include 'Early Sunglow' (yellow) and 'Silver Queen' (white).
Sugar-enhanced varieties produce ears with sweet, tender kernels. The soft kernel pericarps make the corn tender and easy to chew. The harvest and storage periods of se types are slightly longer than standard sweet corn varieties. They also have a higher sugar content. Suggested sugar-enhanced varieties for home gardens include 'Bodacious' (yellow), 'Incredible' (yellow), 'Legend' (yellow), 'Luscious' (bicolor), 'Precious Gem' (bicolor), and 'Silver King' (white).
The common name of the shrunken-2 varieties is derived from the shrunken or wrinkled appearance of the dried kernels. The sh2 varieties are also referred to as supersweets. Shrunken-2 varieties possess the longest harvest and storage periods and have the highest sugar content. However, sh2 varieties have drawbacks. The seed coats on this type are fairly thick, giving the kernels a tougher or crunchy texture. Yields of supersweets are generally lower than standard sweet corn varieties. They are also slow to germinate and have reduced seedling vigor. Suggested sh2 varieties include 'Honey 'N Pearl' (bicolor), 'How Sweet It Is' (white), and 'Northern Xtra Sweet' (yellow).
Synergistic sweet corn varieties combine the desirable traits of standard, sugar-enhanced, and shrunken-2 varieties. The ears of some varieties are composed of 25% se kernels, 25% sh2 kernels, and 50% su kernels. Other varieties have ears that contain 75% su kernels and 25% sh2 kernels. Synergistic sweet corn varieties are sweet, creamy, and tender. Synergistic sweet corn varieties include 'Providence' (bicolor), 'Montauk' (bicolor), 'Applause' (yellow), 'Innovation' (yellow), and 'Mattapoisett' (white).
Augmented shrunken-2 sweet corn varieties are supersweet types that also have the se trait in all their kernels. The kernels of some varieties also contain the su gene. Augmented shrunken-2 sweet corn varieties are sweet, tender, and have a long harvest period. Augmented shrunken-2 varieties include those sold under the Gourmet Sweet™, Xtra-Tender™, and Mirai™ Brand.
Sweet corn performs best in fertile, well-drained soils in full sun. Standard sweet corn varieties may be planted in late April in central Iowa. It's generally recommended that se varieties be planted 1 week later than standard sweet corn varieties. The seeds of sh2 varieties germinate poorly when soil temperatures are below 65 degrees F. As a result, shrunken-2 varieties should not be planted until mid-May in central Iowa. For a continuous supply of sweet corn, plant early, mid-season, and late varieties or plant every 2 or 3 weeks. The last practical date for planting early varieties is July 1.
Sow seed at a depth of 1 inch in heavy soils. In light sandy soils, the planting depth may be 2 inches. Space seeds 8 to 12 inches apart in rows 2½ to 3 feet apart. Sweet corn may also be planted in "hills." Sow 4 to 5 seeds per hill with approximately 3 inches between seeds. Hills should be spaced 2½ feet apart with 2½ to 3 feet between rows.
Sweet corn is wind pollinated. To insure good pollination and ear development, plant several short rows or blocks rather than 1 or 2 long rows. Inadequate pollination results in poorly filled ears.
Since different types of corn can cross-pollinate and contaminate one another, they should be isolated from one another. All sweet corn types should be isolated from field corn, popcorn, and ornamental corn. Shrunken-2 varieties must also be isolated from sugar-enhanced and standard sweet corn varieties. Synergistic varieties should be isolated from shrunken-2 and augmented shrunken-2 varieties. Augmented shrunken-2 varieties should be isolated from standard, sugar-enhanced, and synergistic varieties. Cross-pollination may destroy the quality of the sweet corn.
Isolation can be achieved by planting the different types at least 250 feet from one another and by avoiding prevailing winds. Another method is to stagger planting dates or to select varieties that mature at different times. A minimum of 14 days should separate the tasseling time of the different types.