Only by accident was the weed-killing aspect of corn gluten meal discovered, thanks to research by Nick Christians of Iowa State University. Rather than relying upon manual pulling of annual weeds, or the application of man-made chemical herbicides, gardeners and turf grass managers have a natural, organic product to consider. Gluten acts as a pre-emergent herbicide, killing sprouting seeds. Scattering the meal on the soil's surface, at a rate of 20 to 40 lbs. per 1,000 square feet is standard.
Traditionally used as hog, cattle, dog or bird feed supplement, corn gluten meal is a byproduct of corn milling and the production of corn starch. Gluten is 60 percent protein and 10 percent nitrogen by weight and contains phosphorus.
According to the web site EarthEasy, corn gluten is available in three forms. Unprocessed meal is a fine powder and resembles pollen when scattered onto the soil. The fine particles can be problematic since they fuse to moisture on plant leaves or ground cover mulch rather than fully fusing to the soil surface alone. Granulated gluten consists of slight larger particles that are best applied with a mechanized spreader, while pelleted gluten are coarse and easily spread by hand and best used on lawns where the pellets will remain intact to drop through the grass blades and then dissolve on the soil.
According to research conducted by Nick Christians, corn gluten meal effectively stopped or inhibited the formation of roots on germinating seeds. Sprouting seeds of both grass and broadleaf weed species were killed. Among the common landscape, weed seeds killed include crabgrass and foxtail grass, dandelion, shepherd's purse, speedwell, smartweed, chickweed, pigweed, purslane and lambsquarters. Moreover, as the gluten decomposes, it releases nutrients into the soil, acting as a fertilizer to mature desirable plants already growing in the area.
As a natural organic material, corn gluten degrades once wet and exposed to natural conditions in the environment, such as rainfall, warmth and micro-organisms. Based on various dosages in different soil types, corn gluten continues to suppress seed germination anywhere from 30 to 60 days. After which, another application is necessary. Christians notes that with repeated, consistent use, the number of weed seeds eventually diminishes as they germinate, die and no new sources of weed seeds grow in the treated area.
Corn gluten meal is non-selective in action as an herbicide. That means it will effectively prevent germination or kill young seedlings on a wide variety of plant species, including desired crops in the garden. It does not harm transplanted plants that are placed into a zone treated with the gluten, such as placing large cabbage or tomato seedlings from a nursery into garden rows. One solution to use in flower and vegetable beds is to scatter gluten only in the inter-row areas where you would walk to access the crop rows. Create long, alternating bands/rows or treated and untreated areas, planting your flower or vegetable seeds only in the bands that are free of corn gluten meal particles. Meal can be applied around growing plants without detriment, including interspersed in lawns to prevent the sprouting of weeds.