Corn is a wind-pollinated crop with several different sweet cultivars: Sugary, Sugary Enhanced and Supersweet. Kernels for different varieties come in yellow, white and bi-color. Corn yields can be increased by planting successive crops every 10-14 days through mid-summer, if an early maturing cultivar is used for the last planting, about 90 days before frost. All varieties have similar basic growth requirements and follow the same corn plant life cycle.
Germination may be hindered by cold, wet soil. Sow early cultivars after last frost, when temperatures have reached 50 degrees Fahrenheit, or up to two weeks prior, if soil is warmed for at least a week with black plastic. Plant seeds 1 inch deep and 4 inch apart, in rows 18-24 inches apart. Blocks at least four rows wide are best to ensure wind pollination. Separate individual plots at least 25 feet apart.
Supersweet modern cultivars should not be allowed to cross-pollinate with sugary cultivars. Time plantings with at least 10 days separating pollination periods for each cultivar. Once seedlings are established, thin to 8-12 inches. Mulch to prevent weeds without damaging shallow root systems.
Corn grows in full sun in zone 3 and warmer. A 50-degree (Fahrenheit) soil temperature is required for germination (supersweet cultivars require 60 degree soil temperatures). Avoid high-wind areas. Corn prefers deep soil with a pH of 5.8-7.0, and generous amendments of manure and compost. Water deficiency during critical growth periods can significantly reduce yields and lower quality. Supplement rainfall when tassels are emerging, and while silking occurs and ears mature. Apply compost tea or fish emulsion one month after sowing, and again as tassels appear.
To ensure good pollination, hand-pollinate by gathering pollen from the tassels and spreading it onto the silks throughout the crop. Inadequate pollination results in patchy spots on ear tips. Corn requires 54-94 frost-free days to mature.
Pests and Diseases
Wireworms destroy seeds, and can be avoided by ensuring the soil is warmed thoroughly before planting. Drop mineral oil into immature ears that have sticky substance on their silks, to control earworms. Earlier plantings are more susceptible to corn borers. According to entomologists John Witkowski and Robert Wright, ladybugs and their larvae prey on the eggs and newly hatched larvae of corn borers. Interplant yarrow as a companion plant to attract ladybugs.
Harvest corn when silks turn brown and ears feel full. Pull back husk and press a thumbnail into a kernel. If it squirts milky liquid, the ear is mature. Hold stalk firmly and snap ear downward, then up to harvest. Corn turns starchy within hours, so can or freeze all corn that is not eaten immediately.
Beans and pumpkins are a good combination for companion planting: as the beans use the corn as support for climbing and fix nitrogen from the air and replace what the heavy feeding corn has used into the soil when they die back; and pumpkins smoother weeds and help retain moisture