Corn gluten meal (often simply called CGM) is a byproduct of corn (maize) processing that has historically been used as an animal feed. It can also be used as an organic herbicide.
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In 1985, Dr. Nick Christians of Iowa State University discovered that CGM displayed pre-emergent herbicidal effects during a series of turf grass experiments.[1] The use of corn gluten meal as an herbicide was patented in 1991,[1] but, like many food-related substances used for gardening, is not regulated in the US.[2]
CGM targets a range of plants include small-seeded annual and perennial herbs. It is most frequently used in lawns,[3] but may be applied to gardens and fields as well. Large-seeded weeds seem unaffected.
The corn gluten meal breaks down over time as an organic nitrogen source (NPK rating of 10-0-0).[4]
Proteins in CGM inhibit root formation on newly-germinated seeds, killing the plant. Applications must be timed so that the CGM is present and effective as seeds are germinating.
CGM is applied using a spreader or even by hand: the material is essentially harmless if not inhaled, and is, in fact, edible (though not particularly palatable). On lawns, CGM is applied in early spring (usually timed phenologically by the blooming of crocus or forsythia), and again in the autumn. If the lawn is overseeded, CGM should either be applied at least six weeks before sowing, or two weeks afterwards.
Though very safe to use and nontoxic,[3] CGM should not be applied to areas where it is likely to wash directly into watersheds (it is a nitrogen source). Otherwise it is ecologically safe.
CGM is used as an inexpensive protein source for pet foods. However, some dogs and cats may develop an allergy to corn after eating CGM for an extended amount of time. It is an especially good source of the amino acid cysteine,[5] but must be balanced with other proteins for lysine. It is also used for livestock and poultry feeds.