Home Vegetables Corn Growing and Harvest Information

Corn Growing and Harvest Information

by chuck.mcmullan

Corn is one of the most popular crops for the vegetable garden. Generally speaking, corn takes a large amount of room, water, sunlight, and nutrients compared to other home garden crops, but the rewards can be sweet. There is only one way to truly enjoy the flavor of fresh corn: Grow it yourself – for corn loses much of its sweetness within minutes after picking. True corn lovers start water boiling on the stove before they pick the corn so that they can run the tender ears straight from the garden into the pot.

Corn is a warm-season crop, tender to frost and light freezes. Many types are grown, including field corn, ornamental corn, popcorn, sweet corn, and even broomcorn. Corn may be white, yellow, bicolor, and many shades of red, blue, or even black. Typical sweet corn, probably the most popular for home gardens is usually either white or yellow, we will focus on these. The other types of corn, namely dent or field corn are not commonly grown in the backyard and are more popular with industrial farmers. The field corn is harvested in the dent stage after it has had a chance to dry out, and is either fed to livestock or used in the food industry. Sweet corn is harvested fresh and typically grown near where it is consumed.

The earliest corn matures in about two months, the latest in about 3 months. Many gardeners plant early, mid, and late-season varieties at the same time to extend the harvesting season. Another option to extend harvesting would be to make succession plantings of an early, fast-maturing variety every 10 days or so until midsummer. A second planting should not be made until the first planting has 3-5 leaves. It should be noted that the later sweet corn matures, the more difficult insect control will be.

Where to Grow Corn

Corn requires three months of warm, sunny weather to mature, and can grow wherever ample water is available. In cold, northern climates with shorter growing seasons (65 days) such as Alaska and northern Canada dwarf varieties can be grown.

Recommended Varieties of Corn

There are three major types of sweet or supersweet corn marked to home gardeners. The traditional type is referred to as “sugary” and is typically denoted by the letters “su.” The second type of supersweet corn has a very high sugar content and extremely shrunken seeds due to a small, weak embryo. This type is often marketed as “extra sweet” or “ultrasweet” and is usually referred to by the letters “sh2” for shrunken. The third type is also a supersweet corn. It tends to have a higher sugar content and to maintain or extend this sugar content longer on the plant and after harvest. It is usually referred to as “se” for “sugar extended.” Se corn tends to be very sweet, tender, and crisp and usually retains these qualities after harvest. However, its requirements for warm soil temperatures at germination and isolation from some other corn types at pollination make it more difficult to grow. There are also the ornamental varieties, with colored kernels. These varieties should be grown away from sweet corn, to avoid any cross-pollination. The trick to enjoying an extended corn harvest is planting a span of varieties (early, midseason, and late) to spread the harvest over a long season.

There are several hundred good varieties of sweet and super sweet corn available. Our favorite variety is bi-colored corn called Providence. Incredible is another excellent bi-colored corn. Recommended early varieties include (our favorites are in bold) :

Early – Spring Gold, Seneca Explorer, Early Sunglow, Early Xtra-Sweet
Midseason – Sundance, Wonderful, Northern Bell, Gold Cup, Golden Cross Bantam, Barbeque(yellow), Snowcrest(white)
Late – Seneca Chief, Silver Queen and Country Gentleman Hybrid (white), Sweet Sue, Butter and Sugar (aka Honey and Creme), Sugar and Gold (all bicolor)
Dwarf – White Midget, Golden Midget, Midget Hybrid
Popcorn – White Cloud, Japanese Hulless

Germination60 - 95 F
For growth60 - 75 F
Soil and Water
FertilizerHeavy feeder; apply manure in the fall, or compost a few weeks before planting.
Side-dressingApply every 2 weeks and additionally when stalks are 8-10" and knee high
pH5.5 - 7.0
Seed Planting Depth1/2 - 2"
Root Depth18" - 6'
Height7 - 8'
Width18 - 48"
Space between plants
In Beds8 - 12"
In Rows18"
Space Between Rows30 - 42"
Average plants per person12 - 40
Sweet corn: About 18 days after silks appear, when they're dark and dry, make a small slit in the husk (don't pull the silks down), and pierce the kernel with a fingernail. If the liquid is (1) clear, wait a few days to pick, (2) milky, pick and eat, or (3) pasty, the ear is past its prime and best for canning.
Popcorn: Pick when the husks are brown and partly dried. Finish drying corn on the husks. A solar drier is the most rapid method, drying the corn in about 5 days. The kernels are ready for storage if they fall off easily when rubbed by a thumb or twisted. Before using, store in bags or jars to even out moisture content. The ultimate test, of course, is to pop them. After harvest: Cut stalks and till under or compost immediately.
First Seed Starting Date: 4 - 11 days before last frost date
Last Seed Starting Date: 97 - 127 Days before first frost date
Companionscucumber, melon, pumpkin, squash
Incompatiblestomato (attacked by similar insects)

Soil for Corn

Average garden soil will support a good corn crop, but the best results are obtained when the ground is deeply prepared with well-rotted manure and compost to provide a light, well-draining texture. Corn is a heavy feeder and needs generous quantities of nutrients, especially phosphorus and potash. Work in one pound of 5-10-10 or 4-8-12 per 25 feet of row, or work bone meal and wood ash into the top 8-10 inches of soil before planting. Remove any weeds, rocks, and trash as you work the soil As always, only work the soil when it is dry enough not to stick to the garden tools. If hills are planted, place a scant handful of fertilizer in the bottom of the hill and work it in well before planting the seed.

Planting Corn

Germination in 7-10 days.

When –

Sweet corn is a warm-season crop that germinates and grows poorly during cool weather, and should only be planted when there is no more danger of frost. The soil must be warm (55-60 degrees) and days and nights warm before corn can be planted, as it is susceptible to frost and cool weather. The easiest way to prolong harvest is to plant early, midseason, and late varieties at the same time. If your family has one favorite variety, then plantings (of that same variety) can be made every two weeks until 3 months before the first frost. The supersweet and extra sweet varieties are even more sensitive to cool weather and are not normally planted until the soil temperature reaches 60 F. Corn should generally be planted on the northern side of the garden because they get tall and can easily shade the other garden crops, reducing their yield.

How –

Corn should be planted in a square block area with at least 4-6 adjacent rows of the same variety, never in one long row, as it is open-wind pollinated and needs neighboring corn plants for good formulation of well-filled (pollinated) ears of corn. Gaps in ripe ears are caused by poor pollination. The best planting depth varies with soil types and with the time of planting. Plant deeper in light soils and shallower in heavy soils. Early plantings should be shallower than later plantings because better moisture and warmer temperatures exist near the surface. If late plantings are shallow (1/2 inch) there is less likelihood that the seed will germinate. A good rule of thumb is to plant seeds 3 times deeper than their average diameter. Place rows 3 feet apart. Plant 4-5 seeds per foot, 1/2 – 2 inches deep, thinning to 10-12 inches between plants. (Plant dwarf variety seeds 1 inch deep, 30 inches between rows, 8 inches between plants.) Or place corn in hills 3 feet apart, with 4-5 seeds per hill, thinned to the 3 strongest plants. The seeding rate should be about 1 to 2 ounces of large-seeded varieties or about 1 oz of sh2 types per 100 feet of row. Seeding at this rate will provide a good plant population if growing conditions are favorable.

Corn field

Plant Spacing for small gardens

In areas with unlimited space, sweet corn is usually spaced 10-15 inches apart within the rows, with each row about 36-42 inches apart. A common mistake made by home gardeners is to plant sweet corn in only one or two rows at a time. This typically results in poor pollination and low yields. Sweet corn grows best when planted in several short rows instead of one long row. Corn has male flowers on top of the plant and female flowers called silks at leaf axils along the main stem. The tassel can produce up to a million pollen grains. Pollen moves by wind and gravity, so single rows of corn don’t pollinate and produce as many ears of corn as do rows side by side.

Plant small quantities of sweet corn in rectangular blocks that consist of a minimum of three rows. Plant the seed about 3-4 inches apart in the row, and space the rows 2 1/2 to 3 feet apart. After the plants are up, thin them to 12 inches apart. If planted closer together, the corn will have small, poorly filled ears. In small areas having limited space, but with good soil moisture and organic matter, it is possible to plant double rows that are 10-12 inches apart with 30-42 inches between each double row. Plants within each row are spaced about 12 inches apart. Planting at this spacing will provide good pollination and good yields as long as the blocks are no more than three or four sets of double rows wide and proper moisture, nitrogen, and weed control are provided. This method offers the most efficient use of the garden area. Otherwise plan on spacing the plants 1 foot apart within the row, and the rows about 2-3 feet apart.

Most gardeners know that sweet corn may not be as sweet if it crosses with field corn. Likewise, some of the supersweet or extrasweet corns may not be as sweet if they cross with other types of corn or even with other supersweet varieties. Corn varieties can be prevented from crossing by isolating them from each other. They can be isolated by either planting them 100 yards or more apart or by timing plantings so each variety sheds pollen at a different time. It is also a good idea to isolate different sweet corn types from each other unless the effects of crossing them is established.

How Corn Grows

Corn is a monocotyledon, a grass-like plant, as are wheat, oats, lilies, and orchids. It will grow to 4-7 feet tall on a thick, hollow stalk that supports long (2-3 foot) leathery leaves. As the plant matures, the tassel or pollen flowers will appear at the top, and from the leaf axil the small, sheathed ears will appear, with soft silk threads hanging from them. These are the female seed-bearing parts of the corn plant, the ones that receive the pollen. The ears will swell and develop into corn kernels along a central cob as pollination takes place. Suckers may also develop from corn plants, and sometimes they may even produce an ear. Usually, two ears grow on each corn plant. Once pollinated, corn matures rapidly, usually 15-20 days after the first silks appear.

Corn tassel

Cultivating Corn

Corn must be kept weed-free, and shallow cultivation is important until the tassels appear. Then stop cultivating. The extra “prop” roots will start to develop above ground as the corn matures, and these can be hilled up to give the plants extra strong footing. Watering will be important if the growing season is dry, especially after tassels form. Water deeply weekly if there is no rainfall. Corn has shallow roots, so mulch heavily and avoid cultivating deeper than 1 1/2 inches. In small patches, don’t remove suckers, they may bear corn if well side-dressed.


Sweet corn is a heavy user of nitrogen, so good yields depend upon adequate levels being present. Once it sprouts, it grows rapidly and consumes large amounts of soil nutrients; so it is important to fertilize. When stalks are 6-10 inches tall spread a band of 5-10-5 fertilizer on both sides of each row – about 1/2 pound per 25 feet of row. If you have covered the ground with mulch, pull it aside before applying the fertilizer, or use a water-soluble fertilizer that you can pour over the mulch, and respray at 5-day intervals at least 3 times. When sweet corn is about 2 feet tall, apply 1 cup fertilizer for every 10 feet of row. Scatter evenly between the rows, mix lightly with the soil, and water when finished. Proper nitrogen fertilization is very important to develop a strong tall stalk with the se or sh2 types. Side dress corn twice as it is growing, once when plants are about 6 inches high, and again when they are about knee-high. Spread a band of fertilizer along the row and work in lightly, using either 5-10-10 of 4-8-12 or a favorite organic high in phosphorous and potash. If corn leaves are yellowing or “firing” they need nitrogen.

Weed Control

If fertilized as recommended, weeds will flourish in the rich soil and rob nutrients from the corn. Weeding is vital, but be sure not to damage the corn’s shallow roots. Control weeds by preventing them from becoming established. This means that weeds should be removed while both the corn and the weeds are small. If double rows are grown, a rototiller can be used between each set of double rows, and hand tools can be used between the double rows. If weeds are removed while they are small, corn will grow at a rapid rate and will reduce weed seed emergence as the corn gradually shades the soil.


Sweet corn is a high user of water and requires adequate moisture throughout the growing season to keep from wilting, especially if the double-row technique used. Water may be applied by a trickle or sprinkler irrigation. It should be provided throughout the season but is more important during germination, tassel and silk formation.

Water for irrigation can be applied with a sprinkler. A common mistake of home gardeners is to assume that wetting the surface is all that is needed when using the sprinkler. It is important to wet the effective root zone of the plant. This means that the depth of the soil containing a larger percentage of active roots should be moistened as well. Usually, this is the top 8-12 inches. An easy way to do this is to physically check the depth of wetting after the system has run for a period of time. When the soil is moist to the required depth, shut the system off.

A trickle system can also be connected directly to the household watering system through a hose and filter connections. It only requires 8-10 pounds of inline pressure to operate a trickle system. Plastic hose with properly spaced emitters can be laid down each row to deliver water to the base of each plant. This places water where it is needed most and is utilized the most efficiently. Trickle water systems are more efficient and consume considerably less water than sprinkler systems with the same end results, but are more laborious and costly to install and manage.

Storage Requirements
Corn is best eaten immediately. Some gardeners won't even go pick their ears until the cooking water is already boiling.
TemperatureHumidityStorage Life
40 - 45F80 - 95%4 - 10 days
MethodTasteShelf Life
CannedExcellent12+ months
FrozenGood8 months
DriedGood12+ months

Harvesting Corn

2 1/2 to 3 months. There is an old New England saying that “corn is picked when the cooking water starts to boil”. Corn sugar will start to turn to starch as soon as the ear is taken from the plant. To capture the sweetest flavor, pick just before preparing the dinner, or leave unhusked and refrigerate until cooking time.

In general, harvest corn while it is young, or it will lose its sweetness, as the sugar turns to starch. The best time to pick corn is early in the morning or evening when it is cool. Test each ear for ripeness. Juice from the kernels should be milky white and the kernels should be soft. The silk on the ears should have turned dark brown. The ears should be firm. Kernels on the tips of the unhusked ears should be plump and milky. Sweet corn is not ready when the juice of the kernel is watery. It is overripe when the kernels get large, chewy, and pasty like dough. To harvest ears, hold the stalk below the ear. Twist the tip of the ear toward the ground until it breaks off. To protect your next year’s crop, destroy old corn stalks and stubble, which can harbor corn borer larvae over the winter.

Handling and Storage

If sweet corn is to be frozen or canned, it should be shucked, de-silked, and brought to a boil for a period of three minutes immediately after harvest. Cool it as rapidly as possible after boiling. It may then be either frozen or canned. Immediate processing in this manner reduces sugar loss and greatly improves flavor. Avoid holding sweet corn for long periods of time at ambient temperatures after it is harvested.

Corn Pests

  • Corn earworm – A very destructive pest of corn that works its way down into the ears and destroys the kernels. Control with mineral oil squirted down into the silks 3-7 days after they appear. Some of the newer varieties offer some resistance to earworms: Honeycross, Seneca Chief, Spring Gold, Butter, and Sugar.
  • European corn borer – Corn borers feed on the foliage and internal portions of the stalk. They are usually identified by insect holes bored into the stalk and droppings on the foliage. They will bore overwinter in corn stalks, so fall cleanup is essential. Delay planting of corn to miss the first brood, then plant the mid-season varieties. European corn borer control is difficult for home gardeners because sprays are effective only during the two to three day period after eggs hatch and before larvae bore into the stalks. Pay close attention to the presence of eggs. Eggs are white and one-half the size of a pinhead. They are laid in masses that overlap like fish scales. Eggs darken just before hatching. To control, use the recommended insecticides. Two or more treatments may be needed weekly, since four generations may occur each season.
  • Japanese beetles – Japanese beetles normally congregate on the tip of the ear and feed on the silks. This may reduce pollination and yields. Japanese beetles can usually be effectively controlled by applying recommended insecticides as a foliar spray directly to the silk when it first appears and continuing weekly until harvest.
  • If birds are a problem in your garden, stealing seeds or eating seedlings, cover your corn patch with a floating row cover immediately after planting seeds.

Corn Diseases

  • Corn smut – A disfiguring parasitic fungus that forms large “boils” on stalks, leaves, tassels, or ears, prevalent in hot, dry weather. The case splits apart and spreads inky black dusty spores. At first appearance, the spore cases should be cut off and burned. It is essential to cut off the cases before they burst, as the spores are viable for 5-7 years.

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