Sweet Corn

Sweet corn (Zea mays) is a very tender, warm-season annual. It is picked while the kernels are still immature and eaten as a vegetable rather than dried as a grain. It is one of the taller home garden crops, reaching 5 to 8 feet (152 to 244 cm) tall with a spread of 1 to 2 feet (30 to 61 cm).

Sowing. Sow outdoors only after the danger of frost has passed. Wait for warm soil: do not plant until the soil 4 inches (10 cm) down reaches at least 50 °F (10 °C). Extra-sweet types should wait until the soil reaches 65 °F (18 °C). Some guides set a higher bar, saying standard types germinate well at 55 to 60 °F (13 to 16 °C) and supersweet types need at least 60 °F (16 °C). Use fresh seed, since old seed often germinates poorly.

Depth and spacing. Plant the seed about 1 inch (2.5 cm) deep, which gardening experts also recommends. In light sandy soil, gardening experts allow 2 inches (5 cm). Plant spacing differs by guide: 9 to 12 inches (23 to 30 cm) in the row, 7 to 9 inches (18 to 23 cm), or 8 to 12 inches (20 to 30 cm).

Blocks for pollination. Corn is wind-pollinated, so plant in blocks of at least three or four short rows rather than one or two long rows. A minimum of 12 or more plants is usually needed. Plant in full sun.

Water. Keep the plants uniformly supplied with moisture, especially during establishment, flowering and ear development. Gardening experts ask for at least 1 inch (2.5 cm) of water per week and calls pollination and ear filling the critical periods. Water the soil rather than the plant, because wetting the plant can hurt pollination.

Feeding. Corn is a heavy feeder and needs ample nitrogen. Gardening experts recommend basing fertilizer on a soil test.

Weeds and shoots. Corn roots dislike disturbance, so cut weeds and excess sprouts instead of pulling them, and mulch to reduce weeds. Do not remove the suckers or side shoots; UMD says removing them is not necessary. Tie the stalks with heavy string around the planting to reduce lodging in thunderstorms.

Growing problems. Poor kernel filling can come from dry weather during silking, planting too close, poor fertility, too few rows, or lodging from too much nitrogen. Hot, dry winds and dry soil can also lead to poorly filled ears. Seedlings can rot or die in cold, wet spring soil, so use treated seed.

Pests and diseases. Watch for corn earworm, aphids and flea beetles, and for Japanese beetles, which feed on silks. Corn smut forms white galls on the tassel, stem or ear; planting resistant varieties helps. Raccoons often pick ears early, and an electric fence set up about 2 weeks before the milk stage can help.

When to pick. Pick when the husks are still green, the silks are brown and dry, and the kernels are full size and milky. Puncture a kernel with a thumbnail: clear liquid means it is too early, milky juice means it is ready, and no juice means it is too late. Ears usually mature 17 to 24 days after the first silks appear. To pick, grasp the ear and twist it downward. Gardening experts advise picking in the cool early morning.

Storage. Sweet corn loses sugar quickly, so eat it as soon as possible after picking. Gardening experts suggest storing it close to 32 °F (0 °C) in a moist environment, for about five days. Gardening experts give a maximum storage life of 4 to 8 days when refrigerated. UMD says newer types stay sweet for 2 to 3 weeks in the refrigerator.