Ideally the ground will be moisture retentive but not allowed to ever become saturated during wet spells. Work in plenty of rotted manure or compost the autumn or winter before planting so that it has plenty of time to be incorporated – aim for a bucket load per square metre. This extra organic matter will improve the structure of the soil, increase the level of nutrients available to the plants and help the ground to warm up quicker in the spring (sweet corn needs plenty of heat). About a week before planting out or sowing the seeds add a good scattering of organic fertiliser pellets, such as concentrated chicken manure, and rake the soil level. Don’t worry too much if you missed the opportunity to prepare the plot last autumn, as you should still get good results by digging over the soil this spring and incorporating compost now.
Plenty of sunshine is crucial if the plants are to grow strongly, so aim for a south-facing aspect that will be warm and sheltered. This is probably even more vital to the success of a crop than the soil conditions. Shelter is important as the tall plants will be liable to excessively bend and flex in exposed locations. If you want to sow seeds directly outside in May, then position cloches over the future rows two weeks before the sowing date to warm the soil and speed germination.
Seedlings are not tolerant of frost, which means the earliest you can sow outside directly is mid May. In southern counties you may get away without using cloches or horticultural fleece to warm the soil beforehand, although these will certainly help to make the conditions better. Wait until the soil has dried out slightly before sowing and then set out your seeds in pairs at a depth of 2cm. Space each sowing hole 45cm apart within the row and each row 60cm apart. To maximise the chances of successful wind pollination, plan for a near-square arrangement (see ‘Blowing in the wind’ box).
Alternatively, sow indoors or in a greenhouse from April onwards. Use a quality seed or multipurpose compost. Seedlings hate having their roots disturbed, so sow directly into 7cm fibre pots or home-made versions created using loo roll centres. This will give a good depth of compost for the roots to grow into. They’ll also be able to burst through these make-shift containers, which can be planted whole to reduce the chances of unsettling the roots. Place the seeds 2cm deep in the pots and maintain a minimum temperature of 16°C while they germinate. Once they are through, grow them on at temperatures of no less than 10°C. This shouldn’t be a problem in most greenhouses at springtime.
The seedlings, which look like blades of grass, will appear within two weeks. Remove the weaker of the two to leave one per pot or outdoor sowing station. Keep the covers in place outside as the plants grow, and only remove them once the young plants touch the tops of the cloches or reach 10cm in height under the fleece.
Greenhouse or indoor-raised seedlings can be planted out when they are about 15cm tall and after all chances of frost have gone. Harden them off beforehand by gradually introducing them to their new home over a week or two. Plant them out at the same spacings as you would directly-sown seeds. Water thoroughly to settle the soil around them, and keep the young plants tenderly watered as they establish.
Sweet corn is very easy to grow once plants are established and is rarely affected by pests and diseases. However, to maintain a steady rate of growth you will need to water consistently after the feathery male and silky female flowers appear. At this stage, plants will grow better if given a liquid feed that’s high in potash – any organic tomato feed should do the job, applied as per the packet instructions, usually once or twice a fortnight. You can help the pollination process by gently tapping or shaking the plants after the male flowers appear.
Plants can reach up to 1.8m tall, which means that if your site isn’t well sheltered you may need to individually stake plants by tying them into bamboo canes wedged next to them. Another method of offering extra support is to bank up the soil against the base of each stem into which new roots can grow to anchor the plant. If any roots appear above ground you will, in any case, need to cover them over with soil or compost. Side shoots, known as tillers, may also appear near the base – leave these intact, as removing them can reduce the yield.
Early varieties of sweet corn will yield their first cobs in late July or early August, while the season comes to a close with late-developing types in October. An old American saying advises that you should walk to the plants to harvest your cobs and run back with them – a tradition worth adhering to, because freshness is of the essence! A flat sprint may be a little extreme, but it is true that the high sugar levels that have been bred into sweet corn begin converting to starch within hours of picking. That’s why the taste of freshly-plucked home-grown corn is so superior to shop-bought versions.
You will know it is almost time for picking when the silky tassels on the developing cobs turn a chocolate brown and start to wither. At this point, gently peel back the protective sheath to inspect the corn. Squeeze a kernel with your thumb nail. If a clear liquid oozes out then wait a little while longer, but if a creamy elixir appears then it’s time to pick your crop. If there’s no liquid you have waited too long. Harvest the cobs by twisting them sharply away from the plant, or use a pair of secateurs to cut them free. In a good summer you may get two per plant but don’t be disappointed if you only achieve one.