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. 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. Follow along with this handy How to Grow Corn from seeds Guide and grow food.
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 super-sweet (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 seeds around 7.5cm (3″) apart, 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.
Leave the ears of popcorn varieties on the plants to dry as long as possible into late summer and early fall. The husks should turn yellow/brown as they dry and the kernels should harden. Once the plants appear to be completely dry, or if wet weather is in the forecast, harvest the ears and bring them indoors. Remove the husks. Store the ears in mesh bags in a warm, dry, airy location. The ideal humidity level for curing popcorn is 13 to 14%. Curing is the process after drying that allows for long term storage of popcorn kernels. Once a week, remove a few kernels and try popping them. Popcorn that is chewy or kernels that have jagged edges after popping both mean that the kernels are not dry enough. Continue curing and test-popping until the desired texture is reached. Then remove the kernels and store them in an air-tight container.
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.
Corn is a good companion to beans, beets, cucumber, dill, melons, parsley, peas, potato, soya beans, squash, and sunflower. Avoid planting next to celery or tomatoes. Amaranth makes a great mulch between rows by competing with weeds and conserving ground moisture.