Ask A Master Gardener – Sweet Corn for the Home Gardener

Sweet corn ripe from the garden is one of the best summer treats, yet is one of the most difficult for home gardeners to pull off. Growing this vegetable is made more difficult by the diversity of sweet corn genotypes. All of these come in yellow, white, and bicolor.  There are even some novelty cultivars in red and blueish-black, but the genetics of these is unknown.   Planning now and knowing what type you have can help your chances.

Sixty years ago, this was not as much of an issue as all sweet corn available to the home gardener was normal or sugary, thereby carrying the SU gene. In the 1950s, another gene called the SH2, or super sweet, was discovered followed in the early 1960s by the SE gene, or sugar enhanced.  Today seed catalogs carry corn with each of these genes and cultivars that carry a combination of them.  These genes affect flavor, sugar content, and growth techniques

There is a common misconception that the sweetest corn is white corn. This is not necessarily true, as sugar content is not determined by color.  This misconception often occurs because the first identified corn having the SU gene was white.  The truth, however, is that SH2 cultivars have the highest sugar content and the longest shelf life, and SU cultivars have the lowest. If you have ever purchased sweet corn at a supermarket it is almost always SH2 or super sweet. If purchased at a roadside stand or farmers market it can be anything but is most likely super sweet or sugar enhanced.

To grow at home, your first decision is when to plant. The University of Wisconsin recommends May 10th for SU cultivars and May 25th for SH2 and SE for Dane County.  Dates for Dodge county are similar but since Wisconsin weather is volatile, you may want to rely of soil temperature instead. Take a read with a soil thermometer at or slightly below seeding level and plant SU varieties at 55 degrees or above.  If your seed catalog or packet lists any of the terms SE, SH2, synergistic, augmented, triple sweet or mirai, use the later date or a soil temperature 65 degrees or higher.

Your next challenge includes proper planting. Because corn is wide pollinated single row plantings rarely are successfully pollinated and cross pollination can destroy eating quality. Plant corn in at least three short rows or hand pollinate by cutting two or more tassels when silk emerges from the ears and shake them over the silk.  SU and SE types can be grown near other types without much issue, but all others need to be isolated because pollen from SU, SE, field corn, popcorn or ornamental corn will turn them starchy.  Isolation in Wisconsin can be difficult because there is corn everywhere.  If you cannot make your planting at least a quarter of a mile from other corn, creating a windbreak on the windward side or delaying planting until a week after neighboring plantings will increase your chances of success.

With good weather and luck, you will be harvesting delicious corn about three weeks after the silk emerged. Silks turn brown from the ends, so start sampling your ears when the browning reaches the tip of the ear.

John Shellinger

Certified Master Gardener

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