Corn: Sow and Grow Guide

Corn: Sow and Grow Guide

Corn conjures memories of summer barbeques, warm evenings, and gatherings with friends and family. Because it's such a common food, you might think you know all about it. But there are several different types of corn-for eating fresh, popping, ornamental use, and for flour.

Five types of corn:
SWEET CORN has the most sugar; it is the kind that we eat, and are most familiar with.
FLOUR CORN is high in starch and is usually ground to make cornmeal and flour.
FLINT CORN, also known as Indian corn, is very hard, and comes in many colors. It is grown for livestock feed, and as an ornamental. Popcorn is a type of flint corn, with small, hard kernels that retain moisture until they explode when heated.
DENT CORN is so named because of the dents on each kernel. The kernels are hard, but not as hard as flint corn. It is used for livestock feed and as an ingredient in many commercial foods.

Sweet corn has a few sub-categories of its own:
1) Sugary (su) is the original type of sweet corn with higher amounts of sugar than field corn. For best flavor, su corn should be enjoyed within a couple of hours of harvesting as sugars begin to convert to starch very fast.
2) Sugary enhanced (se) types were first developed in the 1970s. They have higher amounts of sugar and are more tender than su types. The conversion of sugar to starches after harvest is slower, and ears retain their eating quality for a couple days after harvest. Heterozygous se types have 75% su kernels and 25% se kernels. Homozygous se types have 100% se kernels.
3) Shrunken (sh2) gets its name from the appearance of the dried seed kernels. They are also called Supersweet because the kernels contain high sugar levels and hold their sweetness the longest in the field and after harvest. The seed is less vigorous and prone to rotting if sown in cool soil. Newer types of sweet corn such as syngergistic, augmented, and other trademarked types have different mixes of the three main genotypes.

When to sow outside: RECOMMENDED. 1 to 2 weeks after average last frost, and when soil temperature is at least 60°F; ideally 65°?90°F.

When to start inside: Not recommended. Corn does not transplant well, as roots are very sensitive to disturbance, which can cause poor performance as compared to direct sown. If transplanting, corn seedlings are most successful at 2 weeks old; success decreases with age.

Special sowing instructions: Since pollination occurs by wind, corn should be sown in short, parallel rows or blocks rather than one or two long rows.

All sweet corn will cross-pollinate with other sweet corns, field corn, and popcorn. If cross-pollination occurs, the resulting ears are of poor eating quality. To minimize cross-pollination, it is best to stagger sowings of different varieties with similar harvest dates by at least 14 days. Corn that is being grown in a nearby garden or farm can also cause cross-pollination if pollen is being shed at the same time your corn is producing silks.

How many do I plant? Each corn plant produces 1-2 ears. By succession-sowing sweet corn, which has a short storage life, you can prolong the harvest to enjoy week after week of luscious, fresh, sweet corn.


Corn grows best in well-drained soil that is rich in organic matter, and tilled to a depth of at least 10". Sow 2 seeds 1"-1 1/2" deep, 12" apart. Once seedlings are 4" tall, thin to 1 seed per space. Cut the extra seedling off below the ground; unlike other plants it can grow back if only the top growth is removed.

Incorporate a well-balanced, slow-release fertilizer into the soil at sowing time. Corn is a heavy feeder. It benefits from the addition of fertilizer during the growing season, if soils are deficient. Corn needs all three macro-nutrients (nitrogen, phosphorous, and potassium/potash) to be successful, but it needs more nitrogen that the other two. Nitrogen is the first number in the series of three numbers separated by dashes listed in fertilizer analysis, so look for a higher first number, indicating a higher ratio of nitrogen. Liquid fertilizers are taken up by plants more quickly and can be applied more regularly (see fertilizer instructions). Slow-release fertilizer should be side dressed (scratched in around the base of the plant) 4 to 6 weeks after seedlings emerge.

Corn needs a significant amount of water-1" per week. It is important to keep plants watered when tassels emerge and silks appear and during ear formation for best ear and kernel development. For corn types harvested when dry (popcorn, flour, dent), water should be withheld once kernels begin hardening.

Keep plants well weeded, as weeds compete for nutrients and water.

Corn is a grass, and like other grasses, it is wind pollinated. Tassels, which carry pollen, emerge from the top of the plant, usually just ahead of the silks, which emerge lower on the plant and look like long, silky hairs. Each strand of silk needs to be pollinated to become a kernel in the ear of corn. Poor pollination results in "skips" in the ear of corn where a kernel did not form, and leaves a blank space. Once both tassels and silks have emerged, you can ensure good pollination by shaking plants or snapping off a tassel and brushing it against the silks of up to 10 plants, using a new tassel for additional plants.

Sweet Corn
Sweet corn is ready about 3 weeks after the silks appear. Harvest when the silks are brown, but not dried, and the husks are dark green; ears should be plump, and rounded rather than pointed at the tip. To test for ripeness, gently pull back the husk and pop a kernel with your fingernail; the liquid should be whitish; if it is still clear, ears are not quite ready.

Once harvested, enjoy as soon as possible, as sugars quickly convert to starch making the freshest corn the sweetest and most tender. If you would like to store ears, dunk them, with husks intact, in ice water for 1 to 2 hours to cool, to slow sugar loss. Drain excess water. Store ears in the vegetable drawer of the refrigerator in husks, in a container or plastic bag for up to a week.

Dry Corn (flour, dent, popcorn)
Let the ears dry on the stalks. They are ready for harvest when the kernels are hard and you can no longer leave a mark on them with your fingernail. Before the first fall frost, give each ear a twist until it breaks off. Peel back the husks, then hang the ears in a cool, dark, dry place for 4 to 6 weeks to cure. This is important to prevent mold. To strip off cured kernels, twist the cobs back and forth to loosen them (gloves are recommended).

Corn Earworm, also called tomato fruitworm, is one of the most destructive agricultural insect pests in the U.S. Adults are tan moths that lay white, round eggs on corn silks and the undersides of leaves; larvae are 1"?2" long caterpillars, light yellow, green, pink, or brown with white and dark stripes along sides. The larvae feed on the ear tips of sweet corn and the pods of green beans, burrow into ripe tomatoes and peppers, and feed on a wide range of other plants.

There are several ways to control corn earworm. Attract beneficial insects that eat earworm eggs and larvae, such as lacewings, ladybugs, and parasitic flies and wasps, by interplanting pollen and nectar plants. Sweet alyssum is particularly attractive to parasitic wasps. Inspect your developing corn ears for signs of infestation. Two to three days after silks have fully developed and are just starting to turn brown, apply Bacillus thuringiensis (Bt) mixed with vegetable oil to the tip of each ear. Neem or spinosad may also be used in place of Bt; be sure the formulation is approved for use on corn. Alternatively, you can apply a few drops of mineral oil just inside the ear about 5 days after silks appear.

Corn Comparison

Variety Subcategory
(Shape/ Color)
Size Days to
Disease/ Pest
Cold/ Heat
Corn Dent Bloody Butcher Organic HEIRLOOM Seeds 'Bloody Butcher' Dent Heirloom 10'-12' 105-120
Corn Flint Glass Gem Organic Seeds 'Glass Gem' Flint 6'-10' 100-110
Corn Flour Rio Grande Blue Organic Seeds 'Rio Grande Blue' Flour 5'-7' 90-100
Corn Popcorn Dakota Black Organic Seeds 'Dakota Black' Popcorn (butterfly/ snowflake shape) 6' 95-100
Corn Popcorn Robust Pop 400MR Seeds 'Robust Pop 400MR' Popcorn (mushroom shape) Hybrid 6'-7' 95-100
Corn Popcorn Strawberry HEIRLOOM Seeds 'Strawberry' Popcorn (butterfly/ snowflake shape) Heirloom 4' 100-105
Corn Ornamental Striped Japonica Organic HEIRLOOM Seeds 'Striped Japonica' Ornamental/ Flour Heirloom 5'-6' 85
Corn Sweet (su) Honey and Cream Seeds (LG) 'Honey and Cream' Sweet (su)
(bicolor kernels)
Hybrid 7'-7½' 84
Corn Sweet Argent (white) Seeds 'Argent' Sweet (se)
(white kernels)
Hybrid 6'-7' 86 Stewart's wilt, Northern corn leaf blight
Corn Sweet Bodacious (yellow) Seeds 'Bodacious' Sweet (se)
(yellow kernels, adapted for short seasons)
Hybrid 7' 75
Corn Sweet Delectable (bicolor) Seeds 'Delectable' Sweet (se)
(bicolor kernels)
Hybrid 7' 84 Maize dwarf virus, Rust, Northern corn leaf blight, Stewart's wilt
Corn Sweet Painted Hill Organic Seeds 'Painted Hill' Sweet (su)/ Flour
(multi-color kernels, adapted for short seasons)
5' 70 Germinates in wet, cool soils better than other cultivars
Corn Sweet Sugarbaby (bicolor) Seeds 'Sugarbaby' Sweet (se) Hybrid 6' 65 Tolerant to stewart's wilt Good cool weather endurance

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