Position: Sweetcorn is shallow rooted: protection from winds and water loss in the soil is very important. They grow tall: 75 to 170cm (30 to 65in) so take care not to shade other vegetables. Each plant has an average spread of 45cm (18in).
Each plant carries both male and female flowering parts - the cob being the female part and the tassels at the top of the plant being the male parts. Sweetcorn is wind pollinated and best planted in large blocks, where the male flowers at the top of the plant have more opportunity to shed their pollen on the female tassels (where the cobs will form) below. Each plant will produce one or two cobs, so work out how many cobs you are likely to need (you can freeze them) and provide enough space to achieve this.
Prepare the site: Sweetcorn likes free-draining, moisture retentive soil. First remove weeds and dig over the site with a spade, removing any particularly large stones. Level roughly and then work over the area with a rake to leave a fine finish. To ensure your crop gets off to a flying start, spread some general fertiliser granules over the planting area and gently rake in to the surface. If you can, try to do this two or three weeks before planting or sowing. Corn is a heavy feeder, requiring rich soil. Nitrogen is especially important, since corn is basically a grass. An inch or two of compost or rotted manure will also work, as will feeding with fish emulsion.
Timing: Sweetcorn seed does not germinate below 10°C (50°F). Start off indoors in spring or sow directly outside from November. It must have a long warm season to perform well. This means around 70 to 110 frost free days after planting at around 16 to 35°C (61°F to 95°F). Germinates in 10 to 14 days.
Sowing Indoors: Sow indoors in Spring. Start the plants off indoors in cells or pots filled with moist compost. The compost should be moist, but definitely not wet. Wet compost will be cold and reduces the oxygen that the seeds need to germinate. It may even stop the seeds germinating at all. Sow two seeds to each pot. Thin to leave the strongest seedling when they are 2cm (1in) tall. Plants can go into the soil from November. Using a trowel, set sweet corn plants 25 to 30cm (10 to 12in) with 60cm (24in) between rows to form a block. Sweetcorn should be grown in blocks to ensure even pollination. There are no rules about how large the block has to be, this will be determined by how many plants you decide to grow.
Sowing Direct: Sow outdoors once the soil has warmed, from November. You can grow corn by planting seeds directly into the soil in late spring and early summer, but only once the soil is over 15°C (59°F).Use a dibber to make 2.5cm (1in) holes and sow two or three seeds every 25 to 30cm (10 to 12in) with 60cm (24in) between rows. Cover and water. Thin to leave the strongest seedling when they are 2cm (1in) tall. In cooler climates it is worth protecting the emerging seedlings with fleece.
Cultivation: Hoe shallowly when weeding to avoid root disturbance and in exposed areas earth up the stems to 13cm (5in) to increase stability.
Although sweetcorn can tolerate high temperatures and drought, this can lead to poor pollination (empty cobs!). Water regularly, especially if you notice the leaves curling and when the cobs begin to swell. Apply nitrogen fertiliser once the plants are about 20cm (8in) tall and again when they start producing tassels.
Harvesting: Sweetcorn usually matures in February to March, around 85 days from emergence. Look for fat, dark green ears with brown tassels. Squeeze to test for firmness and a rounded, not pointed tip. A final test would be to puncture a kernel with a fingernail. If it spurts milky liquid, it's ready. Simply twist the cob away from the plant. Try to pick and eat the same day as this will give the best flavour and sweetness.