If you have looked for an alternative to synthetic preemergent lawn herbicides that prevent annuals like crabgrass or foxtail, you may have noticed products containing corn gluten meal (CGM). An added benefit of CGM is that it also provides a healthy amount of nitrogen, allowing you to both “feed” and “weed” your lawn at the same time. Does this sound too good to be true?
CGM does inhibit root formation of seedlings and fertilizes the lawn, but certain steps are needed for it to work effectively. Let’s explore how CGM works and what you should consider if you decide to try it.
The corn wet-milling process separates corn into starch, oil, and other products; however, a byproduct is the spent corn kernel. This kernel, lacking starch and germ, still contains a significant amount of protein and is typically called corn gluten meal. CGM is used in livestock and pet foods and, in recent decades, has been marketed as a preemergent herbicide for lawns.
Iowa State University researcher Dr. Nick Christians discovered the herbicidal qualities of CGM. It turns out that the high-protein kernel contains specific amino acids called bioactive peptides that inhibit root formation in germinating seeds.
As CGM slowly breaks down, these peptides are water-soluble, which is beneficial because water applied after CGM helps carry the peptides to weed seeds in the soil. Unfortunately, prolonged rainfall can cause these peptides to leach deeper into the soil, away from the weed seeds. To effectively combat weed seedlings, the material must be spread, watered in, and then left in fairly dry soil for a few weeks so the peptides can prevent root development in germinating seeds. Spreading CGM happens in spring, a time that tends to be quite rainy in Illinois.
For CGM to serve as an effective preemergent herbicide, the bioactive peptides need to be at a higher concentration. That’s why most CGM products recommend applying at a rate of 20 pounds per 1,000 square feet. One drawback of this high application rate is that CGM also contains about 10 percent nitrogen by weight. Applying the recommended amount for herbicidal action results in doubling the amount of nitrogen the grass can absorb.
Applying CGM at 20 pounds per 1,000 square feet is also quite high, and most spreaders can’t dispense that much in a single pass, often requiring multiple applications.
Compared to traditional synthetic preemergent herbicides, CGM is quite expensive. This higher cost makes cheaper knock-off products labeled as “corn gluten” more attractive. However, these products do not contain enough protein to act as herbicides. The EPA requires all products claiming to control weeds to be labeled as herbicides, so look for CGM products that have an herbicide label. If you only want an organic fertilizer without the herbicide effect, corn gluten is an option.
Additionally, long-term use of CGM offers weed control benefits that many people overlook. While we focus on weed prevention, proper fertilization over many years can strengthen your lawn’s resistance to weeds, leading to a more resilient yard.
In summary, CGM can potentially serve as a preemergent herbicide, but certain conditions may limit its effectiveness. University studies often show limited immediate control of weed seeds, but consistent use has demonstrated positive results in preventing crabgrass and other annual weeds. Furthermore, significant value may come from the nitrogen content in CGM, which nourishes your soil and helps your lawn resist weed pressure.
Good Growing Fact of the Week: Contrary to its name, there is no “gluten” in corn gluten meal or corn for that matter.
By Chris Enroth, Horticulture Educator, University of Illinois Extension
