Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/5/03
Contacts:
Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning May 9
Sweet Corn -- An Iowa Summertime Treat
By Richard Jauron
Extension Horticulture Specialist
Iowa State University
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.
Varieties
When purchasing sweet corn, home gardeners can select varieties that produce
yellow, white, or bicolored ears. Several colorful varieties are also
available. 'Indian Summer' has yellow, white, red, and purple kernels.
'Ruby Queen' has reddish kernels. While there are numerous sweet corn
varieties, there are three main types of sweet corn. Standard (su), sugar-enhanced
(se), and shrunken-2 (sh2) types vary in sweetness, length of the harvest
period, keeping quality after harvest, and seed vigor.
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 one or two days. Also, standard varieties don't store well once harvested. Suggested standard sweet corn varieties for home gardens in Iowa include 'Seneca Horizon' (yellow) and 'Silver Queen' (white).
The 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 the 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), '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 also are referred to as super sweets. Shrunken-2 varieties possess the longest harvest and storage periods and have the highest sugar content. However, sh2 varieties do have some drawbacks. The seed coats on this type are fairly thick, giving the kernels a tougher or crunchy texture. Yields of super sweets are generally lower than standard sweet corn varieties. They are also slow to germinate and have reduced seedling vigor. Suggested sh2 varieties 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).
Planting
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 one week later than
standard sweet corn varieties. The seeds of sh2 varieties germinate poorly
when soil temperatures are below 65°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 two or three 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 the seeds 8 to 12 inches apart in rows 2 1/2 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 2 1/2 feet apart with 2 1/2 to 3 feet between rows.
Pollination
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, each type should be isolated. 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. Cross-pollination between the sh2 and se or su varieties will destroy the quality of both. It is not essential to isolate sugar-enhanced varieties from standard 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.
For many home gardeners, one final hurdle must be cleared before the sweet corn can be harvested. The last potential problem is a nighttime raid by masked marauders (raccoons). Unfortunately, we're not the only ones who appreciate the delicious taste of fresh sweet corn. The most effective way to prevent damage to the sweet corn crop is to encircle the area with an electric fence. A two-wire fence with one wire 4 to 6 inches above the ground and the other at 12 inches usually keeps the raccoons out of the sweet corn.
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