Sweet Corn

Sweet Corn

By Josie Borlongan, Garden Guides Contributor

About Sweet Corn

Sweet corn is an annual that grows at least 30 inches and 5 feet (75 cm to 1.7 m) and has an average spread of 18 inches (45 cm). Sweet corn is a variety of maize with high sugar content, which is why it is sometimes referred to as sugar corn. Sweet corn needs a long growing season about 70 to 110 frost-free days after planting. The temperature requirement for planting sweet corn is between 61 and 95 degrees F (16 to 35 degrees C).

Site Preparation

Sweet corn is best planted during frost-free days. Sweet corn seeds will not germinate at soil temperatures below 50 degrees F (10 degrees C). In warm climates, avoid sowing seeds during hot summer days. Sow seeds during spring in their natural environment in place. In cool climates, grow early maturing cultivars in a frost-free sheltered site. Sweet corn is shallow rooting and grows in a wide range of fertile, well drained soils with medium nitrogen. Nitrogen requirements (using fertilizer with 21 percent N content) should be medium, approximately 1.5 to 2 oz. per square yard (45 to 55 g per square meter).

Special Features

Both male and female flowers are carried on the same plant. The male flowers that release pollens are produced in tassels up to 16 inches (40 cm) in length at the tip of the plant. The female flowers (cobs) are silky strands where the ear forms. The strands are sticky and collect the pollens through wind pollination.

Choosing a Variety

The recommended sweet corn varieties are: Early (Early Sunglow, July Gold and Kandy Kwik); Late (Argent, Delectable, Peaches 'n Cream and Silver Quee') and Supersweet (Fantasy, Ilini Extra-Sweet, Indian Summer and Northern Xtra-Sweet). The supersweet types need higher temperatures to germinate and grow and should not be planted with other types because when they are cross-pollinated the sweetness is lost.


In warm climates, plant sweet corn seeds in their natural environment, 1 inch (2.5 cm) deep and 3 inches (7 cm) apart, thinning to the correct spacing after germination. In colder climates, you can plant seedlings indoors in cell packs when temperature reaches 55 degrees F (13 degrees C). Use floating cloches to cover your plants. Remove the float covers at the five-leaf stage. When planting in wet soil, use treated seeds to avoid rotting. Sweet corn seeds may also be planted through plastic mulches. Since the female flowers are wind pollinated, plant in a block rather than a row to ensure good pollination. Plant in blocks at least four plants each way. Leave enough space for growth, approximately 12 inches (30 cm) apart.


When using a hoe to remove weeds, do it shallowly to avoid damaging the roots of the sweet corns. Stabilize the stems in exposed areas to prevent breaking during strong winds. Watering is not necessary except in very dry conditions. Watering at a rate of 5 gallons per square yard (23 ltrs per square meter) is necessary when the flowering starts and when the kernels start to swell. Add mulch to prevent or decrease the rate of evaporation.
Watch out for pests and diseases. Spotted cucumber beetle larvae, asparagus beetles, cutworms, smuts, corn root-worms, armyworms and raccoons have been know to attack sweet corn.

Harvesting and Storage

To avoid deteriorating or losing the sweetness, pick just before required. Sweet corn's sweetness can deteriorate within hours after picking. Supersweet types can retain their sweetness up to three days. Sweet corn freezes well, especially if removed from ears before freezing. To determine if a sweet corn is ready for harvesting, check if the silks have turned brown. Peel back the husks and press into a kernel with a fingernail. The liquid that appears should be milky, a sign that the ear is ripe. If the liquid is watery, it is under ripe and if the liquid is doughy, it is overripe.

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