Corn gluten is a product that can be used for 2 purposes depending on the rate of application.
There is a lot of misinformation out there put forth by advocates of organic and all-natural products that are really hopeful to see a 100% successful natural herbicide invented (authors note: so am I!).
Unfortunately, Corn gluten is not the wonder-product many would like to believe.
Typically it contains approximately 10% nitrogen by weight. (you need to apply 20 lbs. per 1000 sq. ft.) to use for weed-inhibiting activity. (by law, only Health Canada registered products with a PCP# include this recommended rate) other “fertilizer-only” versions are only allowed to offer the 10 lbs./1000 sq.ft. rate.
Corn gluten, the by-product of corn processing, contains proteins that inhibit root growth during seed germination for a number of small-seeded annual and perennial weeds that frequent our lawns, including crabgrass and pigweed. Not only does this product offer a natural herbicidal alternative to toxic “weed and feed” lawn products, but it, also, contains a significant amount of nitrogen that our full-grown turf grass loves.A by-product of commercial corn milling, corn gluten meal contains protein from the corn. It poses no health risk to people or animals when used as an herbicide. With 60 percent protein it is used as feed for livestock, fish and dogs. It contains 10 percent nitrogen, by weight, so it acts as a fertilizer as well.
Applying corn gluten to established weeds, however, will only help them flourish. Corn gluten is most effective when it attacks a weed just before germination or sprouting. Generally, weed germination, specifically for crabgrass, occurs in April and we recommend applying corn gluten in the first few weeks of the month or when forsythias begin to bloom. If you wish to take a more deliberate approach to weed evasion, we recommend purchasing a soil thermometer that reaches at least four inches deep and acting once the soil temperature hits 50 degrees. Once you decide to apply, check the weather forecast and pick a time when it will not likely rain over the next few days. Wet the corn gluten with a soft spray and you are ready to start suppressing weeds!