Sweet Corn

Varieties

There are many characteristics that distinguish between sweet corn cultivars and that affect quality and growing. The majority of sweet corn varieties are often differentiated by three categories based on kernel color: yellow, white, and bicolor (yellow and white) kernels. If white and yellow corn cultivars are grown together, they will produce bicolor corn. If bicolor corn is grown with yellow corn, kernels will be mostly yellow. There is no relationship between the color of kernels and sweetness. Sweet corn cultivars are also divided into different maturity classes based on time to harvest from direct seeding; Early maturity cultivars (mature in less than 70 days), Mid (70-84 days) and Late (more than 84 days). In general, early cultivars produce smaller plants, smaller ears, and have poorer quality than longer season varieties. Longer season cultivars also have more rows per ear and deeper kernels than short-season varieties.

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There are other cultivar characteristics that vary due to variety. Suckers, or weak plants at the base of the plants, seldom produce edible ears. Most modern cultivars do not produce suckers, but some heirloom cultivars do. Suckers, or tillers, are also thought to be a response to damage. Sweet corn husk color varies by variety ranging from light to dark green, green and purplish. The husk cover of ears and a tight husk at the ear tip are important characteristics with improved resistance to worm damage, bird predation, and diseases such as corn smut. Ear size is another important cultivar attribute and in general is correlated to maturity.  Early maturing cultivars have fewer rows (12 to 14) per ear and larger kernels while later maturing cultivars have 18-row ears with smaller kernels that are considered of higher quality. Kernel characteristics are an important factor in eating quality. To reduce biting into the cob, deeper kernels are desired compared to shallow kernels. Medium wide or narrow kernels are preferred to excessively wide kernels as the later must be punctured while biting.

One of the most important quality characteristics is kernel sugar content; sugars are converted to starch as corn matures and after harvest. Sweet corn cultivars are divided into three distinct types in reference to sugar according to genetic background: normal sugary (su), sugary enhanced (se), and super sweet (sh2). There are also varieties that have a combination of these types of genes, with different qualities that are designated as synergistic (sy) or augmented super sweet (shA).

Several hundred sweet corn varieties are grown in the United States and it is important to note their type. Standard, or traditional sweet corn varieties including heirlooms, contain a sugary (su) gene that provides the sweetness and creamy kernel texture of &#;old fashioned&#; corn flavor. This type must be cooked within an hour or two of harvest for best flavor, as sugars begin to convert to starches shortly after picking. Storage life is normally 1 to 3 days under proper conditions for the standard (su) varieties. Sugary enhanced (se) hybrids have the natural sugary enhanced gene that has higher sugar levels (up to twice) than the standard varieties while retaining a similar kernel tenderness and creamy texture. Corn with this gene is sweeter at harvest and maintains quality longer in storage (3 to 5 days) than the standard types. The super sweet (sh2) sweet corn varieties contain a natural mutation which delays the conversion of sugar to starch which allows them to stay sweeter longer (5 to 10 days) than standard (su) varieties. The sh2 gene provides a lower starch content and much higher sugar content, allowing better taste and longer storage. As ears of sh2 corn dry, these lower-starch kernels shrink considerably, hence the name of the gene. Both the se and the sh2 genetic mutations produce a more tender kernel. Many of the newer sweet corn varieties may have multiple combinations of su, se, and sh2 genes on each ear and are called synergistic varieties (sy); they also may be referred to as mixed gene, multi-gene, sweet breeds, or extra tender. These all require isolation distances similar to the sh2 varieties.

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Several sweet corn varieties are available as transgenic seeds. They have been genetically modified to contain the Bacillus thuringiensis (Bt) toxin and/or are Round-up Ready (immune to the herbicide glyphosate) or tolerant of the naturally-derived herbicide, glufosinate. These varieties are of little interest to home gardeners, as they are much more expensive and legal agreements are required with the developer before planting.

To produce ears of corn that are good-tasting and true to variety, do not plant sweet corn with field corn, popcorn or ornamental corn. To maintain the characteristics of the super sweet (sh2) varieties (extra sweet and tender with good storage), they must be isolated from all other varieties except other super sweets.  Isolation distances are far (500 feet apart) because corn, a grass, is wind-pollinated (see below on pollination). To maintain the flavor and characteristics of the super sweet seed planted, a variety other than a sh2 corn variety must not be allowed to grow nearby and add its pollen to the mix. Pollen from other types may supplant the relatively weak pollen of sh2 types and revert back to the starchiness and toughness of field corn. Sugary enhanced (se) sweet corn may be planted next to other sugary enhanced or traditional sweet corn varieties. If you wish to plant two varieties in the same garden, design the plantings with care or pay attention to days to maturity so that varieties do not shed pollen at the same time.

Few heirloom varieties of sweet corn exist; those whose seeds have been carefully saved by growers for more than 50 years. Sweet corn varieties are usually hybrids. Generally, it is not recommended to save seed for future planting with hybrid varieties, as they are usually not expressed properly in the next generation. Most open-pollinated heirloom corn varieties are not sweet corn but are instead varieties used for flour or are dent or flint varieties used for cornmeal or grits. If planning to save your own seeds, plant different varieties feet apart to ensure seed purity.

Table 1. Recommended Sweet Corn Varieties for Louisiana

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