Sweet Corn

Prepared by Karen Russ, HGIC Horticulture Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University. (New 12/99. Revised 04/03. Image added 01/09.)

HGIC 1308

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Planting

Sweet corn (Zea mays var. rugosa) is a warm-season crop that grows best at temperatures between 60 and 80 °F. The optimum soil temperature for seed germination is 60 to 95 °F. Sweet corn does not germinate well in cold soil; therefore, do not plant before the soil temperature at the 4-inch depth is at least 50 F. Wait to plant extra-sweet varieties until soil temperatures reach 65 °F. Planting this crop in wet soil in the early spring will promote seed rot.

Planting Dates
Area Spring
Piedmont April 15 - 30
Central March 20 - April 30
Coastal March 10 - April 30

South Carolina Gardening Regions

Piedmont: Abbeville, Anderson, Cherokee, Chester, Edgefield, Fairfield, Greenville, Greenwood, Lancaster, Laurens, McCormick, Newberry, Oconee, Pickens, Saluda, Spartanburg, Union and York counties.
Central: Aiken, Allendale, Bamberg, Barnwell, Calhoun, Chesterfield, Clarendon, Darlington, Dillon, Florence, Kershaw, Lee, Lexington, Marion, Marlboro, Orangeburg, Richland and Sumter counties.
Coastal: Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Hampton, Horry, Jasper and Williamsburg counties.

Plant sweet corn in rows 3 feet apart with 10 inches between seed in the row. Early, small varieties can be planted 8 to 9 inches apart in rows 30 inches apart. Plant the seed about 1 inch deep.

Sweet corn can be grown on most soil types. This crop requires full sun for optimum productivity.

Plant extra-sweet and standard sweet corn varieties 400 yards apart or plant so that maturity dates are one month apart to avoid crossing.

Types of Cultivars

Two new types of sweet corn have a higher sugar content and hold their sugar content longer after harvest than the standard varieties. The two types are super sweet or shrunken-2 (sh2) and sugary enhanced (se) sweet corn. The shrunken-2 varieties have higher sugar content, slower rates of sugar to starch conversion and more tender kernels than regular (su) or sugary enhanced corn. Varieties with the sh2 gene require isolation from standard sweet corn or the influence of this gene will be masked. Another disadvantage of this type is that the seed is slow to germinate in cold, wet soil in the spring. The cultivars that have the se gene do not require isolation and will germinate in cold soils. Varieties with the se gene have about 50 percent more sugar in the kernels than the standard cultivars.

Recommended Cultivars

  • Yellow: Early Sunglow (Su), Illini Gold (Sh2), Merit (Su), Sugar Buns (Se)
  • White: Silver Princess (Se), Silver Queen (Su)
  • Bicolor: Ambrosia (Se), Chubby Checkers (Se)

Fertilizer

It is best to base fertilizer applications on the results of a soil test. If a soil test is not taken, apply 5-10-10 fertilizer at 30 pounds per 1,000 square feet before planting. Side-dress monthly during the growing season with calcium nitrate at 2 pounds per 100 feet of row. More frequent side-dressing may be required if the garden is sandy or if leaching rains occur.

Watering

Water the garden to provide a uniform moisture supply to the crop. The garden should be watered in the morning so that the foliage is dry before dark. Water sufficiently to moisten the soil to a depth of 6 inches. Light sprinklings will encourage shallow rooting of the plants. The critical periods for water are during pollination and ear filling. This crop requires at least 1 inch of water (rainfall or irrigation) per week for normal development.

Cultural Practices

Sweet corn ripens from 60 to 100 days after planting depending on variety. For a continuous harvest plant early, mid- and late season varieties or make successive plantings of the same variety every 10 to 14 days. This crop is wind-pollinated; therefore, plant in blocks of several rows rather than 1 or 2 long rows to ensure full ears.

High temperature or drought stress during tasseling will result in poor pollination and few kernels on the ears. Weed control is important in this crop. Shallow cultivation and organic mulches are the best methods to control weeds. Cultivation should be shallow to prevent damage to the roots. Organic mulches will conserve moisture as well as control weeds.

Do not remove suckers or side shoots that form on sweet corn.

Harvest

Sweet corn should be ready for harvest about 80 to 95 days after planting, about 20 days after the first silks appear. Harvest corn when the husk is still green and the silks are dry brown. The kernels should be full size and at milk stage. Pick corn that is to be stored in the cool temperatures of early morning. Of course, the best time to pick is just before eating the corn.

Cool the ears as soon as possible after harvest and store as close to 32 °F as possible in a moist environment. Standard sweet corn cultivars lose the sugar from the kernel rapidly at high temperatures. Sweet corn can be stored under optimal conditions for about five days.

Problems

Common cultural problems of sweet corn include poor kernel development caused by dry weather during silking, planting too close, poor fertility, too few rows in a block resulting in poor pollination, and lodging (falling over) from too much nitrogen.

Common insect problems that will be encountered in sweet corn include corn earworm, aphids and flea beetles. Corn earworm is the most common of the sweet corn insects, being found in all areas of South Carolina. Cutworms, seed-corn maggots, Southern corn rootworm, wireworms, fall armyworm, European corn borers, corn (dusky) sap beetles and Japanese beetles may be encountered as pests of sweet corn. More information on corn insects is available in HGIC 2205, Sweet Corn Insect Pests.

Sweet corn is seldom seriously damaged by diseases in the home garden. The following proper cultural practices can reduce many potential disease problems:

  • Obtain seed from a reputable seed source and use a seed treatment fungicide to reduce problems with damping-off.
  • Plant when the soil temperature is above 55 °F to reduce most seedling rots.
  • Keep the garden free of nearby weeds, which can harbor viruses.
  • Remove corn smut-infected ears promptly from the stalks and garden area.
  • Remove plant debris after harvest to reduce diseases caused by rusts and corn smut.

More information on corn diseases is available in HGIC 2204, Sweet Corn Diseases.

Nematodes may be a problem. An effective nematode control program should include crop rotation, sanitation and solarization. More information about controlling nematodes in the home garden is available in HGIC 2216, Root-Knot Nematodes in the Vegetable Garden.

Excerpted from Home Vegetable Gardening, EC 570, 2002.

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.