How to Grow Sweet Corn

Corn seedlingsCorn is a warm-season annual that is best planted after the soil temperature reaches 60°F, usually two or three weeks after the last frost in spring. Corn planted in cold, wet soil is unlikely to germinate. Corn grows best in air temperatures from 60° to 95°F. Corn can take from 60 to 100 days to reach harvest depending upon variety and the amount of heat during the growing season.

Description. Corn is a tender annual and a member of the grass family that can grow from 4 to12 feet tall. One to two ears of corn form on the side of each tall, green, grass-like stalk. Flowering tassels form at the top of each stalk; pollen falls from the tassels onto silky threads growing from each ear below. Each silk is connected to an unfertilized kernel. Each ear of corn forms as many kernels as the number of silks that were pollinated. (Tassels are the male flowers of the corn plant. Kernels and ears are the female flowers.) Kernels of sweet corn can be yellow, white, black, red, or a combination of colors. A large corn variety may form one or two harvestable ears on each stalk. A dwarf variety may form two or three harvestable ears per stalk. When pollination does not occur the stalk will produce only a cob.

Yield. Plant 12 to 20 corn plant per household member.

Site. Plant corn in full sun. Corn grows best in loose, well-worked, well-drained soil with a pH of 5.8 to 6.8. Add aged compost to the planting area before planting. Add aged compost to the planting area the autumn before planting.

Planting time. Corn is a tender, warm-season annual that is best planted after the soil temperature reaches 60°F, usually 2 or 3 weeks after the last frost in spring. Corn requires 60 to 100 frost-free days to reach harvest depending upon variety and the amount of heat during the growing season. Corn grows best in air temperatures from 60° to 95°F. Corn planted in cold, wet soil is unlikely to germinate. Corn seed germinates in 10 to 14 days at 75°F, but the rate of germination may reach only 75 percent. Start corn indoors 2 to 3 weeks before the last frost in spring for transplanting 2 to 3 weeks after the last frost. If your season is long enough, plant successive crops every two to three weeks.

Planting and spacing. Sow corn 1 to 1½ inches deep. Plant seeds 2 to 4 inches apart in short, side-by-side rows to form a block, rather than one long row. You can also grow several plants on mounds or inverted hills. Planting in a block or clump will help ensure pollination. Thin plants from 12 to 18 inches apart for short varieties and 18 to 24 inches apart for tall varieties once plants are 4 to 6 inches tall. Corn planted too closely will require more water and fertilizer and may offer a smaller yield. For a continuous harvest, succession plant corn every two weeks or plant early, midseason, and late varieties at the same time.

Water and feeding. Keep corn evenly moist and regularly watered. Corn grows fast in hot weather and requires an even supply of moisture to avoid wilting. Avoid overhead watering particularly when tassels appear; water hitting the tassels at the time of pollination can reduce the number of kernels on a cob. Add aged compost and aged manure to planting areas the autumn before planting. Corn is a heavy nitrogen user. Side dress corn with aged compost or compost tea when stalks are 10 inches tall and again when they are 18 inches tall and a third time when they tassel.

Companion plants. Potatoes, peas, beans, cucumbers, pumpkins, squash. Do not plant corn with berries or pole beans.

Care. Weed corn early to avoid competition for water and nutrients. Corn is shallow rooted so avoid deep cultivation. Crowding stimulates lots of silage, but no cobs. To protect corn from birds cover ears with paper bags after pollination. Poor kernel development can be the result of poor pollination, too few plants resulting in poor pollination, overcrowding, or a potassium deficiency in the soil. If stalks are purple looking there is likely a phosphorus deficiency.

Container growing. Corn can be grown in a large container but is not a practical choice for container growing because pollination requires several plants. Plant 5 or 6 seeds in a large five-gallon container.

Pests. Corn can be is attacked by cutworms, wireworms, flea beetles, corn earworms, and corn borers. Look for pests and handpick and destroy them. Corn earworms deposit eggs on developing silks; later the small caterpillars will follow the silks down into the ears, where they feed on the tips. Place a drop of mineral oil inside the tip of each ear to coat and suffocate earworms. Corn borers will tunnel into stalks and ears to begin feeding. Handpicking is the best control. Keep the garden free of debris where earworms and borers can live. Raccoons and many rodents will also attack corn. Use traps or fences to exclude these pests.

Diseases. Corn is susceptible to smut, a fungus disease, and Stewart’s wilt, a bacterial disease. Corn smut will turn kernels gray or black and cause kernels to swell. Destroy affected plants, and do not replant in the same place for two years. Smut spores can survive in the soil for two years.

Stewart’s wilt is a bacterial disease spread by flea beetles. Stewart’s wilt will cause leaves to yellow and plants to become stunted. Plant disease resistant varieties and control flea beetles by placing wood ash or agricultural lime around plants.

Harvest. Corn requires from 60 to 100 days to reach harvest depending on the variety and warm weather. Corn is ready for harvest when ears turn dark green, silks turn brown, and kernels are soft and plump; squeeze a kernel and the juice will be milky not clear. Pick corn by grabbing the ear and giving it a sharp downward twist. Each stalk of corn will produces one or perhaps two harvestable ears of corn. Harvest usually comes about 20 days after the silks appear. Harvest corn in the morning and plunge ears immediately into cold water to preserve sweetness.

Sweet Corn Varieties:

Early season, yellow corn: Bodacious (75 days); Earlivee (69 days); Early Sunglow (63 days); IlliniChief (75 days); Sugar Buns (72 days); Tuxedo (74 days).

Mid season, yellow corn: Golden Bantam (83 days); Golden Cross Bantam (90 days).

Late season, yellow corn: Kandy Korn (89 days)

Early season, white corn: Platinum Lady (85 days); Sugar Snow (68 days)

Mid season, white corn: Alpine (79 days); Argent (82 days); Divinity (75 days); Pristine (79 days)

Late season, white corn: How Sweet It Is (87 days); Silver Queen (94 days); Stowell’s Evergreen (100 days)

Early season, bi-colored corn: Athos (67 days); Double Gem (75 days); Quickie (65 days); Skyline (73 days); Sugar and Gold (67 days)

Mid season, bi-colored corn: Butter and Sugar (73 days); Clockwork (78 days); Honey and Cream (78 days);

Late season, bi-colored corn: Pilot (90 days).

Space saving varieties: Baby Corn (65 days); Golden Midget (65 days).


Storing and preserving. Corn is best eaten fresh. Corn will keep in the refrigerator for 2 to 4 day; wrap the unopened husk in damp paper towels. Blanched corn on the cob can be frozen for 3 to 6 months.

Common name. Corn, sweet corn

Botanical name. Zea mays

Origin. Central America