Sweet corn growing - Sweet corn how to grow, tips, varieties, cooking.

Sweet corn is mistakenly regarded as a “no-grow” in Ireland. Many gardeners view it as a semi-tropical vegetable, one that requires intense sunlight and heat to crop, not to mention ripen. This is no longer true, and let me show you why.

The traditional varieties of sweet corn took a long time in the sun to mature and because of this were virtually guaranteed to disappoint over the Irish “summer”. This all changed when along came the F1 Hybrid seed varieties, sweet corn created through selective breeding. The F1 Hybrid varieties are early to mature making them much more reliable.

Check them out….

Sweet corn plant, Click to enlarge, photo / pic / image.

Sweet corn plants, Click to enlarge, photo / pic / image.

Common names:
Corn, sweet corn, sweetcorn, indian corn, sugar corn, pole corn.

Botanical name:
Zea mays

Area of origin:
Central America.

Brief description:
Because it is a member of the grass family, each sweet corn plant comprises lush green foliage similar to wide-bladed grass, growing from a solid central stem. Depending on the variety grown, the plants height can vary from four to 12 feet tall (120-360cm).

Male and female flowering parts are carried on the one plant. Pollen from the male tassels at the top of the plant must fall into the cornsilk of the lower female cob to produce kernels.

Depending on the variety grown the sweet corn kernels can be the common yellow, or perhaps white, black, red, or even a mixture of colours. You will usually get one harvestable corn cob from each stalk, although there is a chance of two or three of reduced size being produced.

Are they easy or hard to grow?:
Relatively easy, provided you receive a long warm summer. This equates to about 90 frost free days after planting, close to 20°C.

Varieties suitable to grow in Ireland:

Sundance (Reliable and early maturing to cope with less than perfect summers, sweet creamy-yellow kernels on cobs up to 18cm (7 inches) long)

Swift also known as Tendersweet (Early maturing and supersweet with a claimed 2-3 times the sugar levels of common Sweet Corn, golden yellow kernels.)

Earlybird (One of the earliest maturing Supersweet varieties, tolerates a colder soil, great eating quality.)

Miracle (Large cobs with golden yellow kernels, good disease resistance.)

Minipop (Bite-sized baby corn, shorter plant so better for a windy site, best grown at high density, does not require pollination to produce cobs)

Irish stock.

UK stock.

When to grow:
Normally mid May sown outdoors. This is provided the soil temperature is above10°C. This soil temp during mid May can be hard to find in many parts of the country. So, many gardeners may place cloches, frames or clear plastic film across the soil for 2 weeks before sowing to warm the soil in preparation.

A safer option in Ireland is to sow indoors in mid April, then transplant outdoors at the end of May.

Where to grow, and soil conditions required:
Sweet corn requires a location in full sun, without shading of any kind. Shelter is also beneficial as the plant is tall but shallow rooted, so is prone to wind rock. Avoid soil that waterlogs or conversely dries out rapidly.

Sweet corn doesn’t grow very well in a strongly acid soil preferring instead neutral to slightly acid soils (5.5 - 7.0 approx). If the pH (relative acidity or alkalinity) of your soil is not suited to the vegetable, then soil nutrients such as Nitrogen, Phosphorus, Potassium, iron, boron, copper, manganese and zinc start to become unavailable, leading to poor crops.

You can use a home soil test available in most garden centres to determine your soils ph. By taking account of the test results you can then decide how much if any amendments are required to bring the to pH of your vegetable garden soil in line.

The application of ground lime will be helpful in countering excessive acidity. As a rough rule of thumb an application of 250g of ground lime per metre squared the autumn before planting/sowing will commonly increase your ph by about one point. However as lime is available in different formulations, I advise also consulting the rates set out on the pack.

If you need to decrease your ph to make the soil more acid, then you can apply sulphate of iron at a rate of 100g per metre squared for each drop in ph point. Apply this product according to the manufacturers instructions and heed safety warnings especially those concerning the use of protective clothing and equipment. An application of 2 inches of peat moss worked in to a spades depth all over the proposed growing area will also go a good way towards dropping your soil by one ph point.

Food reserves required:
For long term feeding of your crop, every 10m2 of growing area should have one wheelbarrow load of well-rotted homemade compost or farmyard animal manure spread over its surface sometime during the autumn/early winter before planting/sowing. Dig this in to a spades depth all over the proposed growing area to enrich it for your crop. Whilst digging, remove any stones and other obstacles that might obstruct roots.

As a rule of thumb, well-rotted manure/compost will be over six months old, and tend to be dark brown will little if any smell. You should not be able to distinguish individual pieces of straw, hay, vegetable peelings, grass etc., as it will all be rotted down.

A week or two before planting/sowing you should also lightly rake into your growing area a well-balanced fertilizer. Growmore or fish blood and bone (organic option) are both suitable for this purpose. Apply according to the rates on the pack.

How to plant or sow:

To sow your seed directly outdoors you will require a weed-free and lightly raked growing area. In this area you should create a series of 1inch (2.5cm) deep holes spaced at 18inches (45cm) apart each way. Create these holes with the tip of your trowel or dibber.

Into each hole drop two sweet corn seeds. Close the hole with soil, then water well and label. Halved clear plastic mineral bottles can be placed over the top to warm the soil and provide a little protection until the seedlings are about 3 in (7cm) high.

To ensure effective wind pollination of the female flowers I suggest you grow your sweet corn in roughly square or rectangular blocks rather than in rows or drills.

The expected seed germination time approx 10-12 days. Any seed not required for sowing that year should be kept dry as it has a life expectancy of 2 years.

When the seedlings are 2cm (1in) tall you should thin them to leave one strong plant at each seed station.

If you are instead sowing indoors in mid April, you can do the following….

Start the plants off on a window-sill or in your polytunnel/greenhouse. Sweet corn hates root disturbance, so I suggest you use peat, cardboard or toilet roll insert pots for your seed sowing. These types of containers allow you to plant your seedling, pot and all into the hole, without the risk of root disturbance/transplant-shock.

The pots (2-in (50mm wide) should be filled with moistened seed sowing compost. Sow two seeds 1in (2.5cm) deep in each pot. Helpful tip: Four hours before you intend to sow you should soak your sweet corn seeds in room temperature water. This will “soften” the seed and hasten germination.

When the seedlings are 2cm (1in) tall you should thin them to leave one strong plant in each pot. Transplant outdoors at the end of May after hardening the plants off. Similar to direct seeding you should space your plants 18inches (45cm) apart in roughly square or rectangular blocks, rather than in rows or drills.

The transplants new growing bed should have been prepared sometime during the autumn/early winter before sowing, in the way as described earlier in this guide. Using a trowel you can pop each pot into its new growing location, all the while taking great care not to disturb the roots. Firm lightly, then complete the task by watering well.

Helpful tip: Four hours before you intend to sow you should soak your sweet corn seeds in room temperature water. This will “soften” the seed and hasten germination.

Caring for your crop:
Keep the soil around the sweet corn plants weed-free. Take care when weeding because the roots are easily damaged.

During a prolonged spell without rain (week or more) you should water gently but deeply once a week. As a rough rule of thumb apply approx 10 litres per metre squared of soil area. Carry out this watering in the morning and try to avoid splashing the leaves, watering the soil instead. Water reserves must be adequate once the cobs begin to swell, or else they may end up empty.

On occasion roots may become visible at the base of the plants. Give these a light covering of soil when they appear. In this way your plants will produce stronger roots to help support them as they grow.

While plants are 20cm (8inches) tall and growing strongly you should apply a nitrogen rich fertiliser such as dried blood. This is an organic feed for leafy plants which is available from most good garden retailers. If you are not bound to organic growing you could instead apply Sulphate of Ammonia (N:P:K 21-0-0) which is another rapid source of nitrogen for green leaved crops.

These fertilisers increase the vegetables vigour and make it less susceptible to plant ills. Once scattered the fertiliser should be lightly scratched into the soils surface (careful of the roots) followed by gentle but deep watering of the soil.

A final feed of dried blood or Sulphate of Ammonia should be applied again when your sweet corn starts producing male tassels at the top of the plant. At all times apply your fertilisers according to the rates on the pack.

Pests and Diseases:

Corn smut is the main fungal disease that affects sweet corn. It attacks the kernels, causing them to swell and turning them dark grey or black.

You should not encounter major problems with this fungal disease though if you follow the soil preparation, plant spacing, feeding, and pH rules mentioned earlier. With any cases of this disease, when you are watering you should try to avoid splashing the leaves which can spread the fungal spores.

If your crop is affected by smut you should destroy any affected plants, and ensure sweet corn not grown same part of the site again for three years.

Other troubles of sweet corn include…
Frit fly

Harvesting, when and how:
Time from sowing to harvest is from 10 to 14 weeks. About three weeks after flowering finishes your cobs should be almost ready for harvesting. The male tassels at the top of the plant should have turned chocolate brown by this stage.

To check ripeness you can pull back some of the green sheath covering a cob and press one or two of the grains with your thumbnail. If a thick milky juice squirts out then you are ready to harvest. If it the liquid is instead watery, I would wait for a few days then test again.

The cobs are harvested twisting them off from the stem. For best flavour your sweet corn should be cooked as soon as it is removed from the plant. When you have experienced the taste of fresh home-grown corn you will really notice how much it looses its flavour if left even 24 hours between harvesting and eating.

Your cobs should be submerged in ice-cold water directly after picking whilst waiting to be cooked.

For short-term storage (one week), wrap the whole cob (including sheath) in damp paper towels and place in the salad crisper compartment of your refrigerator.

Longer-term, the cobs themselves will keep for twelve months in your deep freeze.
To freeze you must boil the corn cobs for 4 to 6 minutes, remove and place under cold water, then freeze in plastic bags, cling film, or tinfoil.

Sweet corn of course is very tasty when boiled. To boil, remove the outer husk, then drop the cob into unsalted boiling water for approx 5 to eight minutes. After draining, serve with a dab of butter.

Divided kernels can also be boiled and used for sweet corn/chicken and sweet corn corn soup

Having a barbeque? Why not roast the cobs on the grill for approx 10 minutes, whilst wrapped in buttered tinfoil.

More debate about this topic on our forum,
click The Irish gardeners forum.

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One Response to “Sweet corn growing - Sweet corn how to grow, tips, varieties, cooking.”

  1. Sylvana Says:

    WOW! This was a very informative post on corn! Corn is everywhere here in Wisconsin, so it is easy to take it for granted that it that it doesn’t necessarily grow everywhere. I have trouble growing it in my own garden for the simple fact that if you don’t have a big enough clump of corn plants, you just don’t get the pollination that you need (as you stated in your post).

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