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Sweetcorn Growing Guide

Sweetcorn Growing Guide

Nothing beats the super-sweetness of freshly-picked corn on the cob. Thanks to the increasing range of varieties suited to the British climate, they can be grown just about anywhere.

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Sweetcorn quick links

How to grow Sweetcorn

Growing sweetcorn in the UK has something of an unfair reputation for being difficult. You only have to look at farmers’ fields in late summer to see great swathes of the stuff gently swaying in the breeze. 

Over the past few decades, considerable effort has gone into breeding varieties suitable for growing sweetcorn at home. These types are reliable, and will crop in the face of a variety of weather conditions. 

The result is a richly-deserved renewed interest in growing sweetcorn. Once you’ve tried it for yourself and realise how easy it is to cultivate, you’ll likely grow it every year! Shop-bought cobs, or Green Giant sweetcorn, really aren’t a patch on home-grown corn – it has to be tasted to be believed.

The best sweetcorns to grow in the UK are the early or mid-season types. Late varieties will produce a crop in milder parts of the country, and are very useful in extending the picking period. In other areas, however, you’ll need to opt for earlier types that will grow quickly and won’t disappoint. 

Sweetcorn is generally wind-pollinated, so it needs to be grown in blocks rather than long rows. If you want to try growing baby sweetcorn, opt for miniature varieties such as ‘Minipop’, which are picked before the female tassels are fertilised. They can therefore be planted in rows and make excellent shelter belts. 

Traditional sweetcorn stalks will produce between one and two cobs per plant. Use this rule of thumb as the basis for planning how many to grow.

Preparing the ground for sweetcorn

This first step is crucial for success in subsequent sweetcorn growing stages. 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. It will also increase the level of nutrients available to the plants, and help the ground warm up in spring. Sweetcorn needs plenty of heat! 

About a week before planting out or sowing the seeds, add a good scattering of organic fertiliser pellets, and rake the soil level. Don’t worry too much if you missed the opportunity to prepare the plot last autumn. 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. This helps to warm the soil and speed up germination.

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Growing Sweetcorn month-by-month

January

Carry on preparing, planting and sowing sites for your sweetcorn as long as the soil isn't wet or frozen.

February

Again, carry on preparing, planting and sowing sites for your sweetcorn as long as the soil isn't wet or frozen.

March

Continue preparing planting and sowing sites for your sweetcorn, as long as the soil isn't wet or frozen.

April

Sow sweetcorn under cover into fibre pots or loo roll centres, so that the roots can break through. Use a seed or multipurpose compost and sow two seeds per pot about 2cm deep.

May

Sow sweetcorn seeds outdoors under cloches or coverings of fleece. Plant out indoor-sown seedlings once all risk of frost has subsided.

Must do this month!
June

Continue planting out sweetcorn. Keep covers in place as long as possible to give the plants a good start. This will also increase the chances of them successfully maturing to flower.

July

Maintain a steady supply of water and high potash liquid feed once sweetcorn flowers appear. Gently tap the plants to dislodge the male pollen.

August

Continue feeding and watering your plants to guarantee the speedy development of your sweetcorn cobs. Stake tall plants in exposed locations.

September

This is the usual month for harvesting sweetcorn, starting with the early varieties and ending with the late varieties. In good years you may continue to enjoy yields into October.

October

Finish harvesting your sweetcorn and then dig up and compost the old plants.

November

Start digging over the site for next season's crop of sweetcorn. Incorporate generous amounts of organic matter as you work the soil.

December

Carry on preparing, planting and sowing sweetcorn sites as long as the soil isn't wet or frozen.

How to grow Sweetcorn from seed

Seedlings are not tolerant of frost, which means the earliest you can sow directly outside is mid-May. In southern counties, you may get away without using cloches or horticultural fleece to warm the soil beforehand. However, 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.

Alternatively, you can try growing sweetcorn in a greenhouse or indoors from April onwards. Use a quality seed or multipurpose compost. 

Seedlings hate having their roots disturbed, so sow directly into 7cm fibre pots or homemade 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 makeshift 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’re through, grow them on at temperatures of no less than 10°C. This shouldn’t be a problem in most greenhouses at springtime.

Spacing out sweetcorn

Sweetcorn may seem like a fairly inefficient crop, as it occupies a large amount of space, but it’s still worth growing even in small gardens. Unfortunately, it’s not really worth growing sweetcorn in pots in the UK or elsewhere, or growing sweetcorn in raised beds in the UK or elsewhere. 

The open habit of the plants, with most of the leafy growth at the top, means that light can penetrate right to the ground. Up to a month before harvest there will still be plenty of light, air and moisture at this low level. So, the ground at the base can be used to cultivate another quick-growing crop. Leafy salads such as lettuce or rocket, radishes, spring onions and even speedy varieties of turnip or dwarf French beans are all excellent choices. 

By the time the sweetcorn plants really fill out, the base plant will have long been harvested. This intercropping technique offers an efficient way of taking advantage of space between plants that take time to reach maturity.

Planting sweetcorn seedlings

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. 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 homes over a week or two. Plant them out at the same spacings as you would with directly-sown seeds. Water thoroughly to settle the soil around them, and keep the young plants tenderly watered as they establish.

Wind Pollination of Sweetcorn

Sweetcorn is in fact a type of grass – specifically, maize. The plants have been bred to develop an exceptionally high natural sugar content within the cob. This makes them suitable for eating unprocessed as a succulent treat in their own right. 

All grasses are pollinated by the wind, rather than by insects. It’s for this reason that sweetcorn is traditionally planted in blocks rather than long rows. The falling pollen will have a greater chance of striking female flowers in a close-knit arrangement.

The male flowers are the feathery, upright blooms that project from the top of the plants. Their exposed position allows them to catch the wind and release their clouds of pollen. The fine pollen particles gradually drift down into the crop to come into contact with the female flowers, which are about halfway down the plants. It is the female bloom that produces the corn cob, once it has been fertilised by the male pollen. 

Female flowers take the form of long tassels, perfectly designed to catch any passing pollen and lock it into place for fertilisation. In still conditions, tapping the plants greatly helps pollination and the formation of more evenly-distributed cobs.

Caring for your Sweetcorn plants + problems

Sweetcorn 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. So, 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. This will help new roots to 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.

How to harvest Sweetcorn

Early varieties of sweetcorn will yield their first cobs in late July or early August. 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. This is 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 sugars in sweetcorn 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’s almost time for picking when the silky tassels on the developing cobs turn a chocolate brown colour 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.

Varieties of Sweetcorn

Sweetcorn varieties to try

'Sundance'

Widely regarded as one of the very best varieties of sweetcorn. It reaches maturity quickly, and will form a decent crop even in poor summers. The 18cm-long cobs are packed with sweet, creamy-yellow kernels that will have you coming back for more.

'Minipop'

Baby corn is delicious in stir-fries or raw in salads – and it’s a great crop to get kids into growing their own. This variety is productive, and the compact cobs taste delicious. It can be grown in a row and doesn’t require pollination.

'Swift'

This is one of the earliest varieties to reach harvest. The medium-sized cobs are exceptionally sweet and tender, and the plants are well-adapted to the unpredictable British summer. It produces a high yield, too!

'Honey Bantam Bicolor'

The stunning cobs form a mix of creamy white and yellow corn kernels that make for an interesting choice. It’s also incredibly sweet, so it’s perfect for eating freshly boiled. The cobs are tender, and are formed early on in the cropping season.

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