Growing Sweet Corn

Growing sweet corn in the home garden can be rewarding and with a little preparation and a good watering regime you can have a bountiful harvest of delicious and juicy corn over the summer.

Growth habits and planting needs

Select a site that gets full sun. Early preparation will ensure excellent rich soil for planting.

Sweet corn needs rich fertile soil and abundant water to grow properly. Prepare the chosen site well ahead of planting by thoroughly cultivating the soil to a depth of 50 cm removing the clods and digging in organic matter like well rotted compost and abundant aged chicken manure to enrich the soil. Preparing the soil 4-6 weeks ahead will allow good decomposition of the organic matter that has been added. Water well during dry weather to encourage this decompositon by soil micro organisms.

Plant a green manure crop in the season before sowing and then slash before the crop sets seed, mulch and turn under the crop. Ideally, corn should follow a legume crop in the crop rotation system beccause of its high need for nitrogen.

Sweet corn needs a pH of 6.0-6.8 so test the soil and amend it by incorporating lime or dolomite if the soil is acidic to raise the the ph and calcium and magnesium available to the plants.

Water the beds the day before planting to assist germination.

Sow the corn seeds 2.5 cm deep and 15 cm apart with rows 20 cm apart. Water in then do not water until the seeds germinate. They will emerge in approximately 4 to 7 days. Stagger plantings over the weeks to ensure ongoing harvesting because the plants will all mature at the same time.

The traditional Three Sisters method of growing corn sets 4 corn seeds in a square on a mound of earth, with a small depression in the centre of the mound to catch rainwater. When the corn is 10 cm tall four beans are planted in between the corn plants on the mound 7 cm from each corn seedling.  Squash is then grown on mounds between the corn mounds to shade the soil around the corn and prevent weeds growing.

The importance of eliminating weeds and not cultivating even close to the surface is highlighted in the following diagram which shows the extensive root system of a corn plant at 8 weeks. Note the root development close to the surfaceeven within the top 7 cm of soil.

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Roots of the sweet corn plant at 8 weeks. Source: Soil and Health Library

Mulching around the corn will supress weeds and avoid root damage while removing them and also retain moisture.

The Three Sisters method of planting also benefits the nutritional needs of the corn plants as they grow. Low nitrogen levels around 30 to 60 days after emergence, when tassels are forming will affect the size of cobs and if nitrogen is low at the time silk is forming the kernel development will be affected. Growing nitrogen fixing beans will ensure adequate nitrogen levels in the soil around the developing corn plants.

It is said that about 60% of the nitrogen needed by the corn will be taken up two weeks before and two weeks after tasselling.

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Sweet corn has high water needs with the critical time from when the tassels are forming, silk is developing and cobs are filling. This is from four to six weeks after emergence at around 60 days.  Lack of adequate water will result in small cobs with poor kernel development. It is especially essential to water the corn well during periods of high heat.

Here is an example of not enough water being delivered to the growing plants. The corn is small but is setting tassel already. The plant is sensing drought and is hurrying to reproduce. It is important to have  consistent and adequate watering of the corn plants throughout their development.

Since this picture was taken the plants have developed small cobs and the plants have only grown to about 1 m in height.

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Once the plants have established the quantity of water should be greater while the frequency can be less. This will depend on the water holding properties of the soil in your area. Ideally delivering 30 to 60 mm of water per week is recommended.

Feed the corn crop with diluted fish emulsion once a week and hill the plants when they reach 50 cm in height. Do this by mounding soil. This will also make the plants more stable and able to stand up up to windy weather.

Side dressing with a thin layer of organic fertiliser or manure about 10 cm from the plants and watering in well  at 4 weeks and again at 6 weeks just before tasseling will improve development.

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Tassels developing

Tassels form over 13 to 20 days at around 6o days from when the seedlings emerge. Moisture is critical at this time and moisture stress will effect the pollination and so cob filling. To prevent diseases like rustavoid wetting the foliage and water in the morning so that the corn plants can dry out during the day.

 

 

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The anthers of the corn plant hanging from the tassels.

Pollen grains fall from the anthers that dangle from the tassels above the plant and fall onto the sticky strands of silk. Over the next day the pollination will occur and if successful the kernels will begin to develop. Each strand of silk is attached to a kernel. Collecting some of the pollen on a tray by shaking the anthers and then spreading the pollen over the silk can help ensure that all the kernels will develop in the eventual cob of corn. The whole process will take about a week.

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The sticky mature silk further down the plant which will catch the falling pollen from the tassels above.

Corn silk can be golden or red as in the picture above depending on the variety. Corn high in acanthocyanin can produce silk of differing colours.

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Mature corn plants with the tassels above and silk showing below.
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Cobs developing after pollination.

When the silk starts to dry and brown the pollination has completed and the within a couple of weeks the cobs will be ready to harvest.

Harvesting

About 20 days from when the silks appear the corn cobs will be ready for harvest. The cobs will have swollen and the kernels filled out and the liquid inside them will be milky when pierced. The silk will have dried out and browned

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A cob of corn ready for harvesting

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Pick the corn early in the day. Hold the cob of corn and pull down while twisting it. It should readily come away from the stalk. Each stalk will have one ear but some stalks like that in the picture above may have  two cobs.

The stalks can then be removed and composted.

Corn is most flavourful soon after picking and the sugars will rapidly begin to be converted into starches so keep the corn in the refrigerator and consume as soon as you can.

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Freshly harvested corn cobs. Image couresy of Pixabay

 

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