One of the highlights of summer is eating fresh sweet corn. Sweet corn hybridizers are constantly striving to develop varieties with improved flavor, seed germination, holding ability and other desirable characteristics.
With so many sweet corn varieties to choose from, selecting one can be difficult. Rest assured that all the varieties we carry are delicious when picked at the right time and grown using proper isolation guidelines.
The Basic Types of Sweet Corn
Varieties of sweet corn are classified based on the type of sweetness genes they contain. Different sweetness genes provide different levels of sweetness and flavor to the ears, and each type has some specific isolation requirements to ensure high quality and flavor.
Normal Sugar (su) Varieties
These are the old-fashioned corn varieties that have limited shelf life. You have to pick them and eat them right away or their sugar will be converted to starch. (Note that freezing stops the conversion process, so freezing right after picking will prevent sugar loss). They offer traditional corn flavor, but the old saying about having the water boiling before you pick sweet corn is quite apt when growing su sweet corn.
Sugary enhanced varieties have a gene that modifies the su gene to increase sweetness and kernel tenderness. Because sugar levels are higher than su varieties, ears retain sweetness longer than su types. There are both heterozygous (1 copy of the se gene) and homozygous (2 copies of the se gene) se varieties. Homozygous se varieties are sometimes called se+ varieties. Their ears are sweeter and more tender than standard se varieties.
Sugary enhanced corns have more of a corn flavor than sh2 types and the kernels are more tender and creamy in texture than sh2 types.
Supersweet varieties contain the "shrunken" (sh2) gene that increases sugar levels and greatly slows the conversion of sugar to starch. These varieties have the sweetest flavor and the longest shelf life of any type of sweet corn. Supersweet ears have kernels that are crisp and juicy in texture.
Because they contain so much sugar and so little starch, the seed of sh2 varieties is smaller than seed of other types of sweet corn, and it appears wrinkled and shrunken. Because of the reduced food reserves to fuel germination, sh2 varieties should be planted when soil temperatures have warmed to at least 60 degrees F to ensure good results.
SSW, or SuperSeedWare, varieties are a new, patented type of sh2 corn that provides all the eating quality benefits of sh2 without the poor germination and seedling vigor. Essentially, the SSW varieties switch off the sh2 genes as the kernels dry, resulting in fuller, less shrunken kernels which germinate better even at cool soil temperatures.
Synergistics are newer varieties which combine both supersweet (sh2) and sugary enhanced (se) kernels in every ear. This provides the benefit of improved sweetness and shelf life combined with the flavor and tenderness of sugary enhanced genes. Usually 25% of the kernels are supersweet and 75% are sugary enhanced, though this can vary among varieties.
Augmented types are similar to synergistic varieties, as they contain both sh2 and se kernels. Unlike synergistic types, all the kernels on the ears contain both sh2 and se genes. This gives them the sweetness of supersweet varieties combined with the tender texture and good flavor of sugary enhanced types.
Basic Isolation Rules
To grow the best quality sweet corn, there are some basics you should know about sweet corn pollination. Planting the wrong types of corn together can result in tough, starchy kernels instead of the expected sweet, tender ears.
First, all types of sweet corn need isolation from all types of field corn, ornamental corn, and popcorn to avoid starchy kernels.
Normal (su) and sugary enhanced (se and se+) varieties can be grown side by side, without isolation. You can also plant more than one su variety or more than one se variety without isolation.
Supersweet (sh2) varieties should be isolated form all types of sweet corn other than augmented varieties. You can plant more than one sh2 variety side by side, and SSW varieties can be grown with supersweet varieties without problem.
Synergistic (sh2 / se) varieties should be isolated from supersweet (sh2) varieties and other synergistic varieties.
Augmented (sh2 + se) varieties need isolation from all except sh2 types and other augmented varieties.
Mirai varieties don't need to be isolated from other types of sweet corns, as they produce only recessive genes, so they cannot affect the quality of other varieties. Some cross pollination of Mirai types by other sweet corn types won't drastically reduce the quality of the Mirai ears, so they don't absolutely require isolation from other corn types. However, to produce the highest quality ears, isolate Mirai varieties from all non-Mirai varieties.
Isolation can be accomplished either through spacing or through timing.
In garden settings, space non-compatible varieties at least 25 feet from other corns in the garden. For larger plantings (acre sized and larger), isolate incompatible varieties by at least 200 feet. In general, larger isolation distances are beneficial and help to ensure there is no unwanted cross pollination.
Isolation can also be accomplished in time by planting varieties that mature 14 days or more apart. This helps to ensure that no pollen from incompatible varieties is present while another variety is producing silks.
All sweet corn requires warm soil temperatures for good germination. For all types other than supersweet (sh2) varieties, the soil should be at least 55 degrees F before planting to ensure good germination. For untreated supersweet (sh2) seed, plant only after soils reach 65 to 70 degrees F. Treated supersweet (sh2) seed can be planted once the soil temperature is at least 60 degrees F.