May's Garden Decisions Will Determine Late Summer Sweetness of Corn

Gardeners who want sugary sweet corn in July and August should choose wisely the varieties they plant in May.

Careful attention to harvesting and handling will help retain sweetness. At optimum maturity, traditional sweet corn will contain as much as 5 to 6 percent sugar. However, over-mature or improperly handled sweet corn can be tasteless.

Standard sweet corn varieties like 'Golden Bantam', 'Hybrid Iochief' and even 'Silver Queen' delight the palate if harvested at optimum maturity. If the corn is harvested a few days later or if left un-refrigerated, much of the sugar is converted to starch. Ears left at room temperature will lose sugar six times faster than those kept at 32º.

For truly candy-like sweet corn, gardeners should try super sweet corns like 'Honey 'N Pearl', 'How Sweet It Is' or 'Hybrid Early Xtra Sweet'. Super sweets contain the shrunken "sh-2" gene, which produces sugar levels two to three times higher than standard sweet corns. Sugar levels will remain relatively high after harvest.

However, super sweet corns have several disadvantages. Super sweet varieties have a tougher seed coat and lack the creamy texture of standard types. The smaller, shrunken seeds of super sweet corns need to be planted in warmer soils (60 to 65º) and half as deep as standard sweet corns (about 1/2 to 1 inch).

Super sweet corn should be isolated from all other types of corn, including regular sweet corn, to prevent pollination by standard sweet corn, which creates starchy, tough kernals.

Sugar-enhanced sweet corns or Everlasting Heritage types like 'Bodacious', 'Kandy Korn' and 'Hybrid Peaches and Cream' are a favorite with many market gardeners. Those varieties contain a sugar-enhancing gene that slows the conversion of sugar to starch, making them sweeter than standard varieties but not as sugary as super sweets. Sugar-enhanced corns will retain their creamy texture and do not require isolation from other sweet corns.

Sweet corns perform best when planted in well-fertilized soil with ample organic matter like compost. Plant in blocks at least four rows wide for good pollination. To prevent cross-pollination, select varieties with different maturity dates. This will also provide corn for the dinner table throughout mid- to late summer.

Plants should be 9 to 12 inches apart, with rows 36 to 38 inches apart. Seeds are planted 1 to 2 inches deep, depending on variety and soil type. Keep plants well watered, particularly at "silking" or pollination. Stressing plants for water at this time can result in poor kernel formation.

Ears are generally ready for harvest about three weeks after silks emerge, depending on temperature. Silks will turn brown within about two weeks. Ears should be harvested when the kernels look milky when punctured with a thumbnail. Harvest in the morning when it's cool to slow the conversion of sugar to starch in the ear.

For more information, please visit New Mexico State University's Cooperative Extension Service (CES) Publications website.