Recent social media posts suggest using household cornmeal to control garden weeds. Looks simple enough, but does it work?
Cornmeal is simply ground corn that we use in cooking. It is an essential ingredient in cornbread and corn muffins. Although it might add some nutrients when sprinkled on the garden, it likely does not have any effect on weeds.
Corn gluten meal (CGM), on the other hand, is an industrial by-product of grain wet-milling. It is used as feed material for cattle, poultry, fish, and dogs. Kelly Allsup, horticulture educator with University of Illinois Extension explains more about using corn gluten for organic weed control in lawns and gardens.
In 1988, Iowa State scientist Nick Christians discovered that CGM is a growth regulator by accident. During an experiment, he studied the effects of five corn derivatives, among them corn gluten meal, on the survival of potted creeping bentgrass. In a surprise result, CMG had a profound effect on the growth and development of the grass, suppressing its growth by 80 percent at the lowest dose applied and 100 percent at twice the dose.
Eager to find out more about the weed-suppressing ability of corn meal gluten, Christians tested it as a herbicide against grasses such as crabgrass. Field tests in the late 1980s that applied 20 pounds of CMG per 1,000 square feet in the spring with another application in the later summer to early fall gave good control. This procedure controlled 60 percent of weeds in the first year, 80 percent in the second, and 90 percent in the third.
He also showed that CMG is an effective pre-emergent herbicide, suppressing other grasses and broadleaf weeds, such as annual bluegrass, black medic, buckhorn plantain, lambsquarters, dandelion, foxtail, purslane, and redroot pigweed. Growers can use it for controlling weeds in strawberries, radishes, onions, garlic, saffron, herbs, and grapes. As a bonus, CMG is an excellent fertilizer.
Allsup notes that success of CMG depends on some environmental factors. "Application timing is critical because it must be done before weed seeds germinate. The highest efficiency is observed during the third and fourth year of treatment. Weed plants that have already germinated will not be controlled," she explained.
Equally important, Allsup noted that CMG must contain 60 percent protein. There are brands on the market that do not contain enough protein to be effective. Allsup also advises against watering the lawn after application, or applying CMG soon after a rainfall, because wetness will reduce its effectiveness.
The take-home message is that a homeowner who would like to try organic weed control with corn meal gluten should acquire the appropriate product, apply it at the right time before weeds germinate, and apply from year to year. Check local garden centers and nurseries to see if the product is available.