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Sweet Corn: How to Plant, Grow, and Harvest Sweet Corn at Home | The Old Farmer's Almanac

Corn

Photo Credit
Pixabay
Botanical Name
Zea mays
Plant Type
Vegetable
Sun Exposure
Full Sun
Soil pH
Slightly Acidic to Neutral
Bloom Time
Summer
Flower Color
White
Yellow
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Planting, Growing, and Harvesting Sweet Corn

Catherine Boeckmann
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Mmm! Homegrown corn has always been a favorite of ours! Want to know how to get the very best full cobs of corn from your garden? Learn how to plant, grow, and harvest sweet corn in the garden for a perfect, oh-so delicious crop!

About Corn

Sweet corn is a tender, warm-season annual crop that produces ears of yellow, white, or bi-colored kernels. A long, frost-free growing season (60 to 100 frost-free days) is necessary to grow and harvest corn.

Native to the Americas, sweet corn has been cultivated for thousands of years; it’s famous as one of the Three Sisters—corn, beans, and squash—grown by Native Americans.

Corn is a Grass! And Wind-Pollinated

A member of the grass family (Poaceae), corn relies on wind to pollinate its flowers! This is why we plant corn in blocks of short rows instead of long, single rows. 

Types of Sweet Corn

Corn comes in early-, mid-, and late-season varieties. Early-season varieties are the quickest to mature, while late-season may take the entire growing season. For an extended harvest, plant varieties with different “days to maturity.” 

There are four main types of hybrid sweet corn: sugary (su), sugar-enhanced (se), shrunken (sh, sh2), and synergistic (sy). Each one contains a different level of sucrose, changing the flavor and texture of the corn. Sweeter varieties will also stay sweeter for longer after harvest. Read more about the differences between these types in the “Recommended Varieties” section below.

Planting

Plant in full sun (at least 6 to 8 hours of direct sunlight). Corn plants are picky about their soil. It should be well-draining yet consistently moist, as corn tends to suck up a lot of water. Ideally, aged manure or compost should be worked into the soil in the fall. If that’s not possible to do, simply mix in aged compost prior to planting.

When to Plant Corn

  • Starting corn indoors is not generally recommended. It’s best to start them directly in the garden so that their sensitive roots aren’t disturbed when transplanting.
  • Corn is very sensitive to frost; do not plant soil temperature is at least 60°F (16°C), or 65°F (18°C) for super-sweet varieties. Usually, this is 2 or 3 weeks after the last frost in spring. It’s vital to plant early, since corn requires a long growing period of frost-free weather. See average frost dates and our Planting Calendar for corn based on frost dates (keep in mind these dates are average or typical and simply a guide).
    • If you live in an area with a shorter growing season, choose an early variety that will mature well before the first fall frost
    • Also, in colder zones, the ground can be warmed by a black plastic cover; sow seeds through holes in the plastic.
  • A couple of weeks after planting your first round of corn, plant another round in order to extend the harvest.

Corn in the garden

How to Plant Corn

  • To speed germination, moisten seeds, wrap in moist paper towels, and store in a plastic bag for 24 hours.

  • Sow seeds about 1½ to 2 inches deep and 2 to 4 inches apart in short, side-by-side rows to form a block, rather than one long row.
  • For decent pollination, we recommend a modest block of, say, 10 to 50 plants.
  • You may choose to fertilize at planting time with a 10-10-10 fertilizer; corn is meant to grow rapidly. If you are confident that the soil is adequate, this step can be skipped.
  • Water well at planting time.

Check out this video for great tips on growing juicy corn:

Growing
  • When the young corn plants are about 4 inches tall, thin them so that they are 12 to 18 inches apart for short varieties and 18 to 24 inches apart for tall varieties.
  • Be careful not to damage corns’ roots when weeding around the plants.
  • Keep corn well watered, as it has shallow roots and can become stressed by drought. About 2 inches of water per week is sufficient; water more if conditions are especially hot or if your soil is sandy. If the soil remains dry, soak the soil again.
  • Side-dress plants with a high-nitrogen fertilizer when corn is 8 inches tall. Repeat when it is knee high (18 inches).
  • Mulch helps to reduce evaporation around the plants.
  • To keep stalks standing straight during high winds, mound soil around the base of 12-inch-tall plants.

  • Wind pollination is critical to develop full cobs of kernels. To help this along, gently shake the the stalks of the plants every few days for as long as the tassels are viable to increase the chances of every silk being pollinated.  Mornings are best. Learn more about corn pollination, including how to hand-pollinate to guarantee pollination success.

Note: Tillers, or “suckers,” are secondary shoots that may develop low on the stalk later in the season. They do not adversely affect the main stalk.

Recommended Varieties

Types of Sweet Corn

Hybrid corn varieties are divided into four main categories based on their sugar content and genetics: sugary (su), sugar-enhanced (se), shrunken (sh, sh2), and synergistic (sy). These categories are namely used to indicate a variety’s sweetness and are usually listed right on the seed packet. It’s important to be aware of which type of corn you’re growing—not only because of the sugar content, but also due to how easily the types can cross-pollinate. If the wrong combination of types cross-pollinates, the ears that are produced may be of subpar quality.

  • Sugary (su) sweet corn is the classic sweet corn. Sugary varieties grow vigorously and are stress resistant. The kernels aren’t too sweet and are said to have a “traditional” taste. However, the sugars in sugary sweet corn quickly turn to starch after the ears are picked, so they need to be eaten right after picking. Do not plant near shrunken or synergistic types.
  • Sugar-enhanced (se) sweet corn is slightly sweeter than sugary varieties. They keep their sweetness for a longer period of time after harvest (a few days) than sugary varieties. They grow well with few issues. Do not plant near shrunken types.
  • Shrunken (sh, sh2) sweet corn—also called “supersweet”—are the sweetest varieties, containing two to three times more sugar than sugary varieties. The sugar in their kernels lasts even longer after harvest (up to a week) than the other types, but kernels tend to be more crunchy and not taste as “corny.” Shrunken types are also more finicky overall. Do not plant them near any other types; hybrid kernels turn out starchy and tough.
  • Synergistic (sy) sweet corn combines sugar-enhanced with one of the other two types to create varieties that have the best of both worlds. Synergistic types tend to have very sweet, tender kernels with a good taste and some synergistic varieties can keep up to a week after harvest. Do not plant near sugary or shrunken types. 

Recommended varieties include:

  • ‘Argent’: sugar-enhanced variety, good taste. White kernels.
  • ‘Iochief’: midseason, normal-sugar variety. Yellow kernels.
  • ‘Luther Hill’: dwarf, normal-sugar variety. Produces 4- to 6-inch ears on 4- to 5-foot stalks. White kernels. Grow at least nine dwarf plants in a block of three or four rows.
  • ‘Silver Queen’: normal-sugar variety. Resistant to some bacterial diseases. White kernels.
  • ‘Sweet Sunshine’: supersweet variety. Disease resistant and high yield. Yellow kernels.

Corn can be a feast for the eyes, too! Look for these ornamental varieties:

Harvesting
  • The warmer the air, the more quickly corn matures. It is usually ripe about 15 to 23 days after silking and sooner if temperatures are exceptionally high.
  • When two ears grow on a stalk, the upper ear matures 1 to 2 days before the lower one.
  • At harvest, ears should be rounded or blunt, not pointed, with tassels turning brown and kernels full and milky.
    • To test, pull down some husk and pierce a kernel with a fingernail. If it’s white, or milky, it’s ready. The milk stage is brief; in hot weather (over 85°F/29°C), sweet corn is at peak for only 1 to 2 days, so check it frequently. Corn harvested a few days after milk stage will not be as sweet.
  • Pull ears downward and twist to remove from stalk.
  • Sugary (su) varieties begin to lose their sweetness soon after harvesting, so use them as soon as possible.
  • Prepare for eating or preserving immediately after picking.
  • If immature corn suffers a late-season frost, the plants and cobs can be damaged and result in the death of the plant or poor-tasting corn.

Corn cob on the plant

How to Store Corn

Wit and Wisdom
  • Baby corn is produced from regular corn plants that are harvested early, while the ears are immature. Regular sweet corn, sugar-enhanced sweet corn, and supersweet corn varieties can be used, along with a few varieties that are specific for baby corn.
  • Corn sometimes produces aerial roots a few inches above the soil. These are not meant to absorb water or nutrients, but rather to stabilize the tall stalk. 
  • A cornstalk grows slowly until it reaches about 24 inches; then it grows 3 to 4 inches per day in hot weather.
  • It’s said that corn planted under a waning Moon grows more slowly but yields bigger ears. Learn more about gardening by the Moon!
  • If your corn shucks harder than usual, prepare for a cold winter.
  • Corn is one of the Three Sisters; its growing style pairs perfectly with beans and squash. Learn more about companion planting.
  • Corn is great for eating but also has so many other uses including medicinal. Learn more about corn for natural health.
  • Learn more fun, witty facts about corn.
Pests/Diseases

Corn Pests and Diseases
Pest/Disease Type Symptoms Control/Prevention
Anthracnose Fungus Yellow/brown/purple/black spots on leaves; sunken, dark spots on stems; spots may develop a salmon-pink, gelatinous mass; eventually, rot; in corn, tops die back and stalks rot Destroy infected plants; choose resistant varieties; provide good drainage; avoid overhead watering; apply compost; use mulch; rotate crops
Corn earworms Insect On corn, eaten silks and kernels; excrement; larvae also attack tomatoes and other plants, eating fruit/pods/leaves/flowers Remove larvae; apply mineral or vegetable oil to tips of corn ears; select corn varieties with tight husks; plant early; add native plants to invite beneficial insects; till soil in fall; spray Bt
Cucumber beetles (spotted) Insect Holes in leaves; plants stunted/die; larvae feed on roots; may spread bacterial wilt Handpick; mulch heavily; use row covers; destroy plants infected with bacterial wilt
Cutworms Insect Wilting; severed stems of seedlings just above or below soil line; whole seedlings disappear Handpick; in spring before planting, cultivate soil to reduce larvae; wrap a 4-inch-wide collar made from cardboard or newspaper around each stem, sinking 2 inches into soil; weed; use row covers; destroy crop residue
Earwigs Insect Many small holes in leaves/stems; corn silks eaten Trap in tuna can filled with 1/2 inch of fish oil and sunk in soil such that edge is slightly above ground level; remove plant debris
Deer Mammal Chewed stalks (especially on young plants); chewed ears Scatter human-scented items, coyote urine spray, or blood meal around plants; enclose corn with fence (at least 8 feet tall)
Downy mildew Fungus Yellow, angular spots on upper leaf surfaces that turn brown; white/purple/gray cottony growth on leaf undersides only; distorted leaves or corn tassels; defoliation Remove plant debris; choose resistant varieties; ensure good air circulation; avoid overhead watering
Flea beetles Insect Numerous tiny holes in leaves, like birdshot from a shotgun Use row covers; mulch heavily; add native plants to invite beneficial insects
Japanese beetles Insect Leaves skeletonized (only veins remain); in corn, damage to husks/kernels/silk; grubs feed on roots Handpick; use row covers; plant tansy near infested plants to lure beetles away
Raccoons Mammal Broken stalks; half-eaten, missing ears Scatter human-scented items, coyote urine spray, or blood meal around plants
Wireworms Insect Seeds hollowed; seedlings severed; stunting/wilting; roots eaten Trap by digging 2- to 4-inch-deep holes every 3 to 10 feet, fill with mix of germinating beans/peas or potato sections as bait, cover with soil or a board, in 1 week uncover and kill collected wireworms; sow seeds in warm soil for quick germination; provide good drainage; remove plant debris; rotate crops
Recipes
Summer Corn Salad
Cooking Notes
  • If too much hot pepper or spice has been added to a soup or stew, adding a can of sweet corn can help.
  • Popcorn is also a favorite snack if you have leftover kernels. Learn how to make homemade popcorn here.
Corn

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Comments

John (not verified)

1 year 3 months ago

Thanks for the excellent growing tips for corn. I live in zone 7a and was surprised to see the planting times. I realize it's a guide but would stress to others that average soil temps should determine actual planting dates. I rarely plant corn before mid may. Last year with the sugar enhanced variety it was May 28th, which according to my log is the latest planting in 30 years of growing corn.
Starting earlier when the soil is cooler than optimal has no advantage and may have the opposite effect when the weather is cool and wetter than normal. Thanks again.

Aaron Olofia (not verified)

1 year 10 months ago

The basic information provided on sweet corn its verities and farming is enlightened indeed.

Thank you from Solomon Islands South Pacific Ocean.

Tracy Diehl (not verified)

1 year 10 months ago

My corn has extra large kernels. Wondering why?

The Editors

1 year 10 months ago

Good question! We looked into a few educational resources and while few explain kernel size directly, they emphasize ear size on which, of course, the kernels form. So, from Purdue University:

Optimum growing conditions set the stage for maximum ear size potential and exceptional grain yields at harvest time. 

(and) Kernel number (ear length) is strongly affected by environmental stresses. This means that potential ear length will vary dramatically from year to year as growing conditions vary. Severe stress can greatly reduce potential kernel number per row. Conversely, excellent growing conditions can encourage unusually high potential kernel number.

See more here https://www.agry.purdue.edu/ext/corn/news/timeless/EarSize.html 

Hope this helps–

Sam (not verified)

2 years ago

When you say brown....could that mean dark maroon? Or is my corn Almost ready for harvest? It's be 83 days. The cobs don't appear to be very big. I'm in zone 8a and my stalks are in a raised garden bed.