How to Sow
- Growing corn is easy provided you have enough space and plenty of sun. Corn is wind-pollinated, so you need to plant in blocks to ensure pollination. You should have a minimum 10 foot by 10 foot area. The exception to this rule is ‘On Deck’ corn, which has been bred to grow in containers. If you are growing ‘On Deck’, choose a container that is at least 24 inches wide and deep and plant nine seeds evenly spaced.
- Corn is classified as Sh2, SE, SU, or SY. These refer to the sweetness and how long the corn may be stored. Sh2 is is supersweet, lasts 4-6 days in the refrigerator and is more challenging to sow in cool soils; SE is sugar-enhanced and lasts over a week in the refrigerator; SU is normal sugary, more cool soil tolerant but with a shorter shelf life; SY combines SE and Sh2 traits. Isolate Sh2 corn varieties from others by planting seeds at least 250 feet apart, or select varieties that mature at least 2 weeks apart, so they will not cross pollinate.
- When choosing a site for corn, plant on the north side of your garden so the tall plants do not shade other plants in your vegetable garden.
- Corn is a warm season crop and should not be planted in cool soils. The non Sh2 varieties tend to be more tolerant of cool soils, but in general the soil should be about 65 degrees F or warmer.
- Sow corn seed 1 inch deep, 5 to 6 inches apart in rows 2 to 3 feet apart.
- Seedlings emerge in 7-14 days.
- When corn seedlings are 3-5 inches tall and healthy, thin to 1 foot apart.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating.
- Keep plants well watered during dry periods to promote uninterrupted growth. Corn needs 1-2 inches of rain per week for best production. Use a rain gauge to check to see if you need to add water. Corn is also a heavy feeder and will benefit from side dressings of fertilizer applied as directed through the growing season.
- Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
- Suckers tend to form at the base of the plants; they help support the stalks and make food for the plant. The stalks may have to be staked in windy areas, but in general they are self-supporting.
- Sunflowers are good companion plant for corn. Direct sow sunflowers in rows parallel to corn rows to help separate corn varieties that need isolation from each other. Choose sunflower varieties of comparable height to the corn plantings. The sunflower border, with vibrant hues in russets to golden-yellow, will add sparkle next to the almost all-green corn plot. The ‘Three Sisters’ (corn, bean and squash) are traditional companion plantings with Native American gardeners.
Harvest and Preserving Tips
- Ears of corn are ready to harvest about 17-20 days after the silks appear. The kernels should be firm. Open an ear and pierce a kernel with your fingernail. If the liquid is watery, the corn is not ripe yet. It should be milky. If it is creamy, it is overripe and will not taste as sweet.
- Firmly grip the ear and twist downward to harvest. Take care not to break the plant when harvesting the first ear, or the second ear will not develop. Most corn produces two ears.
- Store unhusked corn in the fridge and consume as soon as possible. Sh2 and SE varieties keep the longest in the fridge, up to one week.
- Corn freezes well after blanching and may also be canned using a pressure cooker. Immature ears may be pickled.
Common Disease Problems
Bacterial Wilt: This causes yellow streaking on the foliage. It is soil borne and spread by flea beetles. Burpee Recommends: Rotate crops and control flea beetles. Many hybrid corn varieties are resistant.
Corn Smut: This fungus infests corn ears causing them to expand and turn black as they fill with fungus spores. The ears become quite disfigured. The disease can also affect the foliage. Burpee Recommends: Remove and discard all infected plant parts as soon as you see the disease. Rotate crops as the disease can overwinter in the soil.
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation.
Leaf Blights: This causes tan spotting on the foliage and causes plants to lose vigor. Burpee Recommends: Rotate crops. Check with your Cooperative Extension Service for fungicide recommendations.
Rust: A number of fungus diseases that rust colored spots on foliage, stalks and husks. Burpee Recommends: Plant early as these diseases tend to be worse later in the season. Plant resistant varieties. Practice crop rotation. Remove infected plants.
Common Pest and Cultural Problems
Corn Earworm: This very destructive pest lays eggs on corn silks and the larvae tunnel into the ears and feed on the kernels at the tip. Burpee Recommends: Some varieties are tightly husked and tend to be resistant. You can apply mineral oil to silks every 2-3 days to help prevent damage by the larvae.
European Corn Borer: This insect overwinters as a worm in corn stalk plant debris. They emerge in spring as yellow/brown moths which lay their eggs on the undersides of corn leaves. The larvae feed on pollen and plant tissue and bore into the stalks. They can damage ears and damage stalks to the point of breaking. Burpee Recommends: Look for signs of boring in the plant stalks, which will be holes. You can try to probe the stems and kill the borer if possible. Rotate crops and remove plant debris at the end of the season. Check with your Cooperative Extension Service for pesticide recommendations.
Flea Beetles: These small hopping beetles feed on plant foliage and spread diseases. Burpee Recommends: Rotate crops with plants in a different plant family. Use floating row covers to prevent damage to young foliage.
Japanese Beetles: Burpee Recommends: Hand pick early in the morning into a bucket of soapy water.
Raccoons and other Mammals: Raccoons, ground hogs and deer, as well as birds can be a problem. Burpee Recommends: Ground hogs and raccoons may be trapped. It is difficult to control deer without fencing.
Corn FAQs
Does corn have to be direct sown, can I start it indoors? We recommend direct sowing corn, not starting it indoors. Transplanted corn is prone to stunting or exhibiting deformed growth.
Why do I have spotty germination on my Sh2 corn? The sweeter the corn, the warmer the soil must be for sowing. Sh2 varieties require a warm soil, at least 65 degrees F, and can rot in the soil if they are sown in cooler soils.
Why is my corn leaning over? Corn grows buttress roots and suckers to stay upright: shallow or undeveloped roots will cause the plants to lean over in rain or wind. Use a balanced fertilizer to grow strong roots. Check for soil pests that would stunt roots. Heavy rains and soil erosion can also undermine corn plants.
Why don’t my ears of corn have kernels? Every individual silk makes a corn kernel. Incomplete pollination of every silk will cause spotty kernel formation. Corn plants require even, consistent moisture. Plants need cross pollination to develop full ears. If corn is stressed by high temperatures or too little water it can tassel early and the pollen can die on the tassels before the silks are produced.
Why did my On Deck corn not produce ears? There are a number of possible reasons for this, including too cool or too warm temperatures, too little or too much fertilizer, too little water or not enough sun. A very common cause of this is that the container is too small or the plants are overcrowded. In our trials we have found that the smallest container that will produce good quality corn is 24 inches in diameter and depth, with nine plants. Smaller containers or too many plants will cause nutrient deficiencies and water stress because of the restricted space.