Having 8+ years of experience with growing field corn and a master’s degree in crop science, I thought I knew all there was to planting sweet corn; however, my first time planting it was a flop. I planted the seeds as if I was raising 350-bushel field corn (who doesn’t want lots of sweet corn?), which resulted in lodged sweet corn plants. Come to find out, you don’t plant sweet corn exactly the same as field corn.
Sweet corn is sweeter than field corn due to a “sugary (su) gene”; sugary enhanced (se) and supersweet (sh2) varieties are also available, and to make the deal even sweeter, there are varieties with a combination of two and even three of the sugary genes; synergistic (sy) and augmented supersweet (shA). Depending on your sweet tooth, you have some options for sweetness level.
When planting sweet corn, it should be planted in a block formation rather than a single, long row to allow for the plants to be closer together for adequate pollination. Without pollination, corn kernels will not develop on the ear. The recommended spacing for planting sweet corn is 8 to 12 inches apart in rows 2.5 to 3 feet apart, with seeds being planted about 1 to 2 inches deep. Sweet corn does not tolerate cooler temperatures, so it is best to wait until soil temperatures have reached at least 60F (2-inch depth).
Corn is a nitrogen-loving plant, so it is important to apply nitrogen for healthy growth. Ideally, it is best to apply nitrogen in split applications. A preplant application of a general-purpose fertilizer (10-10-10) can be applied at 25 lbs per 1000 sq ft. Sidedress recommendations vary and can be custom fitted to growing conditions. It is best to get the young plants off to a good start, so an additional nitrogen application is recommended when the plants are 6 to 12” tall; apply 1 to 2 lbs of actual nitrogen per 100 feet of row. Spread fertilizer between the rows or on either side of a single row and lightly incorporate into the soil. It is recommended to make 2 to 3 sidedress applications throughout the growing season.
Sweet corn requires about 1 inch of water per week. Heat and moisture stress during pollination and grain fill can result in poor kernel set, so it is important to make sure plants get enough water during this time. During pollination, drip irrigation or soaker hoses are the best methods for providing additional moisture.
It is important to always start with a clean, weed-free planting area. Once the corn is planted, light, shallow tillage can be done to control weeds between rows; however, avoid getting too close to the root system of the plants. Mulching with grass clippings, straw, etc., can also be used to keep weeds down. Herbicides are also an option, but be sure to read your label for proper application.
Corn earworm, European corn borer, corn rootworm, and Japanese beetles are the most common insect pests of sweet corn in the Midwest. Some sweet corn varieties have the Bt (Bacillus thuringiensis) protein to help protect against corn earworm and European corn borer. For varieties without the trait, Bt is also available as an insecticide spray for high insect pressure. Corn rootworm beetles and Japanese beetles can cause issues with pollination as they often feed on the corn silks. Other problematic insects of sweet corn include fall and common armyworm, corn flea beetle, black cutworm, and corn leaf aphid. It is always best to scout the crop periodically to check for the presence of insects and insect damage. Control is not necessarily warranted unless damage or insect numbers have reached a threshold. Threshold information for sweet corn insects can be found in Purdue Extension's Sweet Corn Pest Identification and Management guide.
The diseases we see most often in sweet corn are Gray Leaf Spot (GLS) and Northern Corn Leaf Blight (NCLB). These two diseases overwinter on crop residue, which is why we often see it every year. Crop rotation, tillage, and resistant varieties are the best management practices for these diseases. Common smut is often seen when plant tissue is wounded by hail, wind, or mechanical damage. Conditions that negatively affect pollination can also lead to the presence of smut. Anthracnose leaf blight and stalk rot, as well as crazy top and common rust, are often seen in wet years as these diseases favor a moist environment. Southern rust can also be an issue in sweet corn; however, it is only an issue when the pathogen is blown in from the south and we have a hot, humid environment. Most of these diseases can be controlled through the use of resistant hybrids (if available), burial of crop residue, crop rotation, or application of fungicide. The Sweet Corn Pest Identification and Management guide is again a useful resource in identifying diseases and figuring out how to best manage them.
In addition to insects and disease issues, it is also common to face problems with vertebrate pests such as birds, raccoons, and deer. These can be a bit more difficult to control. The most common method of control includes an electric fence to keep raccoons and deer out. To keep bird damage to a minimum, it is suggested to select varieties with tight husks or good tip cover. Typically, the earliest and latest ripening fields are subject to the greatest damage, so try to plant at a similar time as neighbors. Repellents can be used for smaller home garden plantings but can be costly on a larger area basis. Repellents are most effective when coupled with other tactics, such as electric fences, to deter wildlife. If wildlife becomes too much of an issue, consult your state wildlife agency about the laws and regulations pertaining to shooting and trapping wildlife.
Depending on the variety, sweet corn can take 60 to 100 days to mature. By making successive 2-week plantings, sweet corn can be enjoyed for a longer period of time. Sweet corn should be harvested at the “milk stage,” which is when the kernels are fully formed but not completely mature. Once the silks dry out, start checking the firmness of the ear and the fullness of the tip kernels. Check frequently to make sure the ears do not become too mature. After picking, it is best to eat, can, or freeze the corn sooner rather than later before the sugars decrease and starch content increases.