By Linda Naeve
Urban Agriculture Specialist
Iowa State University Extension
Many homeowners strive to have a healthy, weed-free lawn yet at the same time are concerned about the effects of herbicides and synthetic fertilizers on the environment. If you fit that description, there is an effective, all-natural product that will ease your conscience and reduce weed growth in your lawn and garden - corn gluten meal.
Corn gluten meal (CGM) is a natural by-product from the wet milling process of corn. It contains 60 percent protein and is used as a supplement in feeds for livestock, poultry and pets. The idea of spreading CGM on lawns to control weeds came quite by accident and through close observation. In 1986, Nick Christians, professor of horticulture at Iowa State University, was using CGM as a growth media in a study of turfgrass diseases. During his research, he observed that the CGM reduced grass seed germination. Curious about the possibilities, he directed his attention to finding out if and how this was possible.
Christians' research revealed that a naturally occurring compound in the protein faction of CGM had an inhibitory effect on the root formation of germinating seeds. In 1991, he was granted a patent on CGM as a natural, preemergence herbicide for use on all crops. As a preemergence herbicide, CGM only controls germinating seeds and has no effect on weeds that are already established. Currently, it is labeled for control of crabgrass, barnyard grass, foxtails, dandelion, lambsquarter, pigweed, purslane, smartweed and several others at the time of germination.
During the past 10 years, CGM has gained national attention as being the first effective "organic" herbicide. It is marketed and distributed under several trade names.
As a weed control product, CGM is available in two forms, powdered and granulated. The powdered form is the same as that sold at mills for animal feed. Although both forms are effective, the granulated form is easier to apply.
Proper timing of the application is critical for good weed control. Apply it in late March to mid-April, at least three to five weeks before the crabgrass seeds germinate. Spread it evenly over the lawn at a rate of 20 pounds per 1,000 square feet and water it lightly into the soil. After watering, let the soil dry out somewhat so that the sprouted weed seedlings dry up and die. CGM can also be applied in mid-August to control late-season annual weeds.
Besides its high protein content, CGM also contains 10 percent nitrogen by volume, making it an excellent, natural, slow-release fertilizer for lawns. It promotes thicker lawns resulting in fewer places for weeds to become established.
CGM can be used to control germinating weeds in established perennial flower gardens. It can also be used in a vegetable garden after transplants and seedlings have become established. Follow label recommendations for application rates.
CGM has some limitations and variability as an herbicide. For example, results may not be obvious after a single application the first season. Control improves with every year it is used on lawns. It is often more expensive than other preemergence herbicides. Also, extensive rainfall or irrigation after application can reduce its effectiveness.