Until 1986, corn gluten meal was simply a corn milling byproduct. No one had thought to use the meal for any other purpose, until Iowa State University researchers noticed the corn gluten meal suppressed seed germination. The byproduct is now a useful, natural herbicide that also acts as a nitrogen fertilizer.
Animal feed manufacturers use the meal byproduct as an inexpensive source of protein. In addition to a high protein content, corn gluten meal also contains 10 percent nitrogen. Nitrogen is the primary ingredient in most lawn fertilizers and encourages both deep green color and fast growth. At the recommended application rate of 20 pounds per 1,000 square feet, this equates to a generous 2 pounds of nitrogen per 1,000 square feet.
Most homeowners use corn gluten meal to suppress weed seeds rather than to fertilize lawns. It cuts new weed germination rates by 50 to 60 percent without resorting to synthetic and sometimes dangerous herbicides, but does not affect growing weeds or perennial weeds. After four to five years of regular use, however, it fully controls weed growth. The nitrogen also contributes to a thick, weed-free lawn.
The nitrogen in corn gluten meal breaks down over time, acting as a slow-release fertilizer. This reduces chances for fertilizer burns on the lawn and ensures a long-lasting release. Corn gluten meal is not a complete fertilizer, however, and lacks phosphorous and potassium; test your soil and add these nutrients as necessary.