Successful Edibles Series
Grow Sweet Corn, a Summertime Staple
As seen in the Yadkin Valley Magazine, May-June 2021 Issue
What is summer without corn on the cob? Best tasting when eaten fresh, sweet corn is worthy of your precious garden space and labors. Corn is also an excellent succession crop; sow a new planting every two to three weeks to spread out the harvest, and revel in sweet corn all summer long.
Corn (Zea mays) is in the grass family, Poaceae with other grain crops: wheat, rice, millet, and sorghum and sugarcane, from which we extract sugary sap. Compared to field/silage corn, sweet corn is higher in sugar content, between 8 to 50%, and has genes that slow the conversion of sugar to starch. Other types of corn of interest in the home garden are flint/dent corn for grinding, popcorn and gourdseed corn (aka indian corn), an ancient corn used as early as the 1700s and the ancestor of modern corn cultivars.
Most of the sweet corn grown today are hybrids, cross-bred and selected for the best qualities; yellow, white and bi-color varieties are available. There are also different genetic types (“genotypes” or “types”), coded as “su”, “se”, “sh”, or “syn”, on packets of seed or in a catalog. These types have the following characteristics:
- Sugary (“su”) or normal is the old-fashioned favorites like Silver Queen; though less sweet than the other types, their creamy texture is loved my many. Su varieties lose half their sugar in 24 hours post-harvest, tasting best if eaten the day of harvest. They also make excellent freezer corn.
- Sugar enhanced (“se”) has increased sugar content and longer shelf life (3 or more days in the refrigerator). Popular se varieties are Kandy Korn and Bodacious, the latter favored by home gardeners for its short height.
- Supersweet/shrunken-2 (“sh2”) is considerably sweeter, up to three times the sugar content of su and se types. A gene that slows the conversion of sugar to starch helps retain their sweetness longer (up to one week), but the creaminess and “corn” flavor of older varieties is lacking. Honey ‘n Pearl is a reliable sh2 variety.
- Triplesweet/synergistic (“syn”) combines the sweetness genes of se, sh2, and su for high sugar as well as storability. Honey Select is a proven variety winner that has produced well in the Yadkinville Community garden. Other stand outs in recent trials are Café, a good early season variety, and Providence, for its remarkably long, white ears.
Sweet corn is a pollinated by wind, and can potentially cross-pollinate with other corn crops tasseling at the same time and produce undesirable results. For example, cross-pollination of sh-2 with se and su types can lead to starchy unpleasant kernels. Isolate white from yellow and bi-color corn for a pure white ear, though the taste will be unaffected. Sweet corn should be separated from field corn by a minimum of 300 feet (100 yards) or at least 14 days in maturity. Wait two weeks between plantings of different varieties if cross-pollination is a concern.
Planting & Growing
Corn seeds germinate poorly in cold, wet soils, so do not rush your first planting. Sweet corn should be planted after the threat of frost is passed, the end of April for USDA planting Zone 7 (most of Yadkin county), but May is safer. Normal sugary (su) corn can be planted at soil temperatures above 55 F, (the best choice for early plantings), but the newer types need soil temperatures in the high 60s and 70s to germinate. Old wisdom advises that planting sweet corn should begin the white oak leaves are as big as squirrels’ ears, a useful phenological sign to time plantings.
Corn is a heavy feeder that grows best in consistently moist, fertile soils. Before planting, have your soil tested for an accurate fertilizer and lime requirement. In the absence of a soil test, apply one to two cups of a general fertilizer like 10-10-10 per 10 ft of row. A pre-plant fertilizer with higher phosphorus promotes root growth for rapid plant establishment. When plants are two feet tall, supplement with a nitrogen fertilizer applied as a side dress. Alternatively, use a high N organic fertilizer such as blood meal, bone meal, fish emulsion, or composted animal manure. Plant corn following a leguminous cover crop that adds nitrogen to the soil.
Poor pollination, close plant spacing, or stress (e.g. hot, dry weather) induced during the pollination window can result in undeveloped, poorly-filled ears. Plant corn in blocks at least four to five rows wide to optimize pollination by wind and to avoid a preponderance of blank kernels.
First, work the soil into smooth seedbed and remove weeds, rocks and soil clods. Form rows 2 to 3 feet apart, and direct seed at 1 inch depth (½ inch in colder soils) and 3 to 4 inch spacing, thinning later to leave 8 to 12 inches between plants. Cover the seed with soil and gently tamp. Wetting the furrow before sowing can keep clay soil from crusting and creating a barrier that hinders seedling emergence.
Consistent watering and weed management early in the crop lifecycle will help plants withstand pests. Be prepared to irrigate when there is insufficient rainfall, particularly in the 2 weeks before silking until the ears have formed. Use shallow cultivation with a hoe and a garden cultivator or mulch to control weeds in rows. Later, a canopy of leaves will shade row middles and discourage new weeds.
The main pests of sweet corn are most abundant in the latter season (August – September), and damage can be avoided by planting in early May. Common insect pests are flea beetles, European corn borders, fall armyworm, and importantly, corn earworm. Corn earworm larvae are large (up to 1 3/4 inches length) with alternating green, brown or pink stripes. The caterpillars feed directly on developing kernels, reducing the harvestable yield. Carbaryl (Sevin) and Bifenthrin are chemical controls available to homeowners, but they must be sprayed on the ears three to five times during silking to be effective. Deter vertebrate pests, like corn-loving raccoons, with a loud radio, electric fencing, a dog near the garden, or live animal traps.
Harvest usually lasts from July to mid-October in our area. Once silks have dried and turned brown, puncture the husk with your fingernail. If milky juice is released, the corn is ready to harvest. If the liquid is clear, the corn is immature; if there is no sap, it’s too late. Except for su-type varieties, which taste best on the day of harvest, sweet corn maintains good flavor for two to three days in the refrigerator. With sweet corn, the reward is greatest if freshly picked.