These big plants will grow in almost any soil, but getting the cob to mature is another matter. The maturity of the ears (cobs) is not controlled by the size of the plant, nor by day-length, but by the accumulated heat the plant has had while it grew. They call this the "heat units". Only temperatures above 50 F count after the last killing frost of spring. Temperatures above 50 F add up to create the heat units. Please read "Farmzone" for further information on heat units in your area.
Corn plants generally grow very tall, and will shade other vegetables. Some plants will benefit from this shade, such as lettuce, but heat-loving plants must be placed so that the corn does not shade them. This heavy-feeding plant also provides a stalk for plants such as Pole Beans.
Season & Zone
Season: Warm season
Zone: 4 to 8 - dependent more on summer heat than zone.
Plant between May 15th and June 10th. If the soil is not warm enough, seeds often rot before sprouting - especially when not treated with fungicide. Untreated corn seeds should be planted only when the soil has warmed up above 18°C (65°F) - warmer for supersweet (sh2) types, and even warmer for a good stand. Use a soil thermometer. If spring weather is cold, consider planting in flats indoors with bottom heat for transplanting. Seeds should germinate in 7-10 days. If it rains after planting and corn does not emerge, just replant the area.
Plant 2-5cm (1-2") deep (shallower for sh2 seed or cool soil). Sow 4 seeds per 30cm (12"), in rows 60-90cm (24-36") apart. Because corn is wind pollinated, plant in a block (or circle) of at least 4 rows.
Ideal pH: 5.8-6.8. Corn is a heavy feeder, so add manure or compost, and use 500g (1 lb) of complete organic fertilizer per 6m (60') of row, mixing it thoroughly into the soil beneath each seed furrow. Thin to at least 20-25cm (8-10") apart in the row. Large eared and double-eared varieties need to be 30cm (24") apart. Keep free of weeds until knee-high, and then leave it alone. Use the days to maturity listed for comparative purposes among the varieties only - your garden may be different.
When the silks at the top of an ear are a dry
brown, the cob seems to start to droop and the kernels release milky
juice when cut.
In optimal conditions at least 75% of seeds will germinate. Usual seed life: 2 years. Per 100' row: 400 seeds, per acre: 87M seeds.
Diseases & Pests
Disease: Prevent disease and nutritional exhaustion of the soil by using 4-year crop rotation and composting old stalks.
Pests: Wireworms are a bad pest in home gardens. Loopers are pale olive-green caterpillars up to 2.5cm (1") long. They chew into the centre of young corn plants and can kill the plant if the growing tip is damaged. Seed corn maggot is a small, legless maggot that attacks germinating seed. Planting in warm soil or using predatory nematodes may help prevent seed-destroying soil creatures.