8/12/2019 Growing Sweet Corn Organically

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Sweet corn is a warm season crop requiring averagetemperatures of 16 OC to 24 OC for optimum growth, and80 - 110 frost free days from germination to harvest. Ifyour growing space is limited this may not be a

suitable crop as well grown plants can reach 1.5 - 2metres and often produce only one to three cobs per plant.

The plantSweet corn, Zea mays, is a cereal crop originating fromCentral America.

The plant is monoecious, meaning it produces distinctmale and female flowers onthe same plant. The flowerspike at the top of the plantis the male flower whichsheds copious quantities of

pollen over several days.The female flower appearsas a bunch of silky tassels inthe leaf axils. Pollination is

by wind.

Site and soilThe site should be open andsunny but not subject to verystrong winds which canknock the shallow rooted

plants over. The soil should be well structured and richin organic matter as sweetcorn is a moderately heavyfeeder.

It is an ideal crop to followlegumes or green manure ina crop rotation and will

benefit from the residualnitrogen left in the soil by these plants.

Soil pH should be 6.5 and the addition of lime ordolomite prior to planting will be necessary if it is below5.5.

PlantingCorn can be either direct sown or transplanted asseedlings in late spring or early summer once the riskof frost has passed. Most books suggest two or threesuccessive plantings at three week intervals. InCanberra, the warm season is not always long enoughand later plantings (January) may not succeed.

Sow the seed 20 - 30 mm deep and space the plants 30

cm apart. It is common to plant pairs of seed and if both germinate the weaker seedling is removed. Theseweaklings can be transplanted if you wish and will

usually crop adequately. Seedlings emerge in 4 - 10days. Plant corn in a block rather than a long row formore even and reliable pollination.

CultivationSweet corn has a moderately high water requirementand needs adequate and even soil moisture throughoutthe growing season, particularly at the flowering and

pollination stages. Avoid overhead watering atflowering as this may disrupt pollination. Pollination isa critical stage and uneven or undeveloped kernels willresult if the plant is nutrient or water stressed at thistime. Unfavourable weather conditions - either too hot

and dry or too wet - may alsoaffect pollination and result inuneven kernel set.

Sweet corn is a shallow rooted plant and deep mulching is usefulto help maintain even soilmoisture. Drip irrigation underthe mulch is the most efficientmethod of watering. Leaf rollingis a sign of water stress and canoccur on hot dry days even ifthere is sufficient soil moisture.

Pests and diseasesSweet corn plants are generally

untroubled by disease or insect pests. Heliothis caterpillars may be an occasional problem and candamage the tips of ripening cobs.The main pests are mice and

birds which can quickly destroymost of the harvest. Netting thecrop after flowering will preventmost bird damage.

HarvestingCobs are harvested by twisting them off the main stem

when the silks have turned brown and dried and thekernels near the tip are well filled and have started tocolour. The sheath can be peeled back from the top ofthe cob to check kernel maturity. Very hot weathernear maturity can result in rapid deterioration of thecobs which become tough and starchy. Sweet corn is

best eaten as soon as possible after harvest but willkeep for a few days if refrigerated.

References Dimsey,R 1995, Sweet corn production , AG0378

State of Victoria DPI Bird, R 2003 Growing Fruit and Vegetables

Adrienne Fazekas

GROWING SWEET CORN

Canberra Organic Growers Society www.cogs.asn.au Autumn 2008