Growing Sweet Corn
Sweet corn (Poaceae Zea mays) is a member of the grass family and, other than sweet sorghum, is the only member of that family that is intentionally grow in the garden.
There are many types of corn, including popcorn, sweet corn, dent corn, pod corn, flour corn and flint corn. Sweet corn is distinguished from other corns by its high sugar content when in the milk, early dough stages and wrinkled, translucent kernels when dry.
Sweet corn is a warm-season vegetable that can be easily grown in any garden with sufficient space. It is especially popular with home gardeners because it tastes great harvested fresh from the garden.
Sweet Corn Planting Time
Sweet corn requires warm soil for germination (above 55 degrees Fahrenheit for normal sugary sweet corn varieties). Early planting should be made in mid to late April if weather permits. Sugar-enhanced and supersweet varieties will not germinate in cool soil and should not be planted until soil temperatures are above 60 degrees Fahrenheit. Sweet corn may be planted from late April until mid-July. The success of the crop will be limited by cold weather at the beginning or the end of production.
For a continuous supply of sweet corn throughout the summer, plant sweet corn two weeks apart. Once three to four leaves have appeared on the seedlings from the previous planting, you can make a second planting of the same variety or successive plantings of a late variety or your favorite main crop.
Sweet Corn Spacing and Depth of Planting
Plant the kernels (seeds) 1/2 inch deep in cool, moist soil and 1 to 1 1/2 inches deep in warm, dry soil. Space the kernels 9 to 12 inches apart in the row. Plant two or more rows of each variety side by side to ensure good pollination and ear development. Allow 30 to 36 inches between rows.
Plan your garden arrangement and planting schedule to prevent cross-pollination between your sweet corn, field corn and popcorn. If sweet corn is crossed with field corn or popcorn, it will not develop a high sugar content and will be starchy. Isolation of supersweet corn from all other corn is necessary to allow the full potential of sweetness of the kernels to develop. Cross-pollination between yellow and white sweet corn varieties affects only the appearance of the white corn, not the eating quality.
Soil Preparation for Sweet Corn
A deep, well-drained, fertile, sandy loam soil is the ideal soil type. The soil pH needs to be above pH 6.0. If the soil pH is too low, liming the soil will be necessary. Use a soil test to determine specific requirements of the crop. Corn benefits from deep plowing before planting and cultivation during the growth of the crop. This will promote a strong root system and help prevent lodging (falling over) of the cornstalks.
Care for Sweet Corn
Sweet corn will require about 1 to 1 1/4 pounds of nitrogen per 100 feet of row to produce a crop. Corn is moderately sensitive to salts, and care must be taken to avoid salt injury. The most effective way of applying fertilizer is to band it 2 inches to the side and 2 inches below the seed. Half of the nitrogen should be applied prior to planting and the other half when four to five leaves are fully expanded. Sweet corn benefits from a split application of fertilizer. This is quite important on sandy soils with low organic matter content because nitrogen is easily leached from these soils. The second application of nitrogen (for example, urea) is made when the corn is approximately knee-high (12 to 18 inches tall).
Phosphorus and potassium should be applied before the crop is planted. The most effective way of applying phosphorus is banding it at the rate of 1 1/10 to 1 2/10 pounds per 100 feet of row. If soil potassium levels are high, excess application will not improve the crop.
Cultivate shallowly to control weeds. Although corn is a warm-season crop, lack of water at critical periods can seriously reduce quality and yield. If rainfall is low, irrigate thoroughly during emergence of the tassels, silking and maturation of the ears.
Hot, dry conditions during pollination result in missing kernels, small ears and poor development of the tips of the ears.
Some sweet corn varieties produce more side shoots or “suckers” than others. Removing these side shoots does not improve yields.
The practice of removing the tassels from the stalk is a research and breeding practice and is not a gardening practice.
Cultivars of Sweet Corn
Incredible (yellow), Bodacious (yellow), Temptation (bicolor), Delectable (bicolor), Argent (white); all sugar-enhanced.
There are three distinct types of sweet corn that may be divided according to their genetic background: standard, supersweet and sugar-enhanced.
Standard sweet corn varieties contain a “sugary gene” that is responsible for the sweetness and creamy texture of the kernels.
Supersweet varieties contain a unique gene that makes the kernels sweeter than those of the standard varieties. The sugar of the supersweet varieties is also converted to starch more slowly, preserving the sweetness for a longer time. The kernels of the supersweet varieties have a crispy texture and contain low amounts of the creamy texture that other sweet corn varieties possess. Although this lack of creamy texture is not especially noticeable in fresh corn on the cob, it affects the quality of frozen and canned corn.
Sugar-enhanced varieties contain multiple gene combinations that impart a creamy texture and increase sweetness. The sugar content is not as high, however, as that of the supersweet varieties, but the texture is better.
Standard sugary sweet corn is the first to be planted in the spring. Seed will germinate in cool soils (near 60 degrees Fahrenheit). Isolate this type from popcorn, field corn and supersweet sweet corn or the flavor will be starchy.
Sugar-enhanced sweet corn has less seed vigor and requires warmer soil temperatures to germinate. Isolate this type from popcorn, field and supersweet sweet corn for the best flavor.
Supersweet sweet corn has a high sugar content and shrunken kernels that are weaker and need warmer soils (above 60 degrees Fahrenheit) to germinate. Isolate this type from popcorn, field corn and sugary sweet corn or the flavor will be starchy.
|Days to Maturity
|Disease Resistance or Tolerance
|Maize dwarf mosaic virus
|Large, white ears, excellent quality, widely adapted
|Maize dwarf mosaic virus
|Good yields, large yellow ears, good quality
|Sweet yellow kernels
|Burgundy stalks, red husks
|Honey and Pearl
|All-American Selection, bicolor
|How Sweet It Is
|White supersweet type, plant in warm soil, All-American Selection
|Recommended for baby corn and late season bicolor
Harvesting Sweet Corn
Days to maturity – 63 to 100
Harvest when the husk is still green, silks are dry and brown, kernels are full size and yellow or white in color to the tip of the ear and at the milky stage. Use your thumbnail to puncture a kernel – if the liquid is clear, the corn is immature; if milky it’s ready; and if no sap, you’re too late. Cover unharvested ears checked by this method with a paper bag to prevent insect or bird damage. Experienced gardeners can feel the outside of the husk and tell when the cob has filled out. Corn matures 17 to 24 days after first silk strands appear, more quickly in hot weather, slower in cool weather.
Each cornstalk should produce at least one large ear. Under good growing conditions (correct spacing; freedom from weeds, insects and diseases; adequate moisture and fertility), many varieties will produce a second ear. This second ear is usually smaller and develops later than the first ear.
Sweet corn ears should be picked during the “milk stage” when the kernels are not fully mature. This stage occurs about 20 days after the appearance of the first silk strands. The kernels are smooth and plump, and the juice in the kernels appears milky when punctured with a thumbnail. Sweet corn remains in the milk stage less than a week. As harvest time approaches, check frequently to make sure the kernels do not become too mature and doughy. Other signs that suggest the corn is ready for harvest are drying and browning of the silks, fullness of the tip kernels and firmness of the unhusked ears.
To harvest, snap off the ears by hand with a quick, firm, downward push, twist and pull. The ears should be eaten as soon as possible, processed or refrigerated. At summer temperatures, the sugar content in sweet corn quickly decreases and starch content increases.
Cut or pull out the cornstalks immediately after harvest and put in a compost pile. Cut the stalks into 1-foot lengths or shred them to hasten decay.
Approximate yields (per 10-foot row) – 5 to 10 pounds or roughly 10 to 20 ears.
Amount to raise per person – 20 to 30 pounds or about 40 to 60 ears.
Storage of Sweet Corn
Refrigerate immediately to prevent sugars from turning to starch. In cold (32 degrees Fahrenheit), moist (95 percent relative humidity) conditions, sweet corn will keep 4 to 8 days, but standard varieties will become starchy after a few days.
Preservation of Sweet Corn
Sweet corn can be frozen on or off the cob or canned.
Author: Brandy Brabham, WVU Roane County Extension Agent – Agriculture and Natural Resources