Chemical herbicides are a tempting alternative to pulling weeds by hand or hoeing them out of a garden. The potential damage to the environment, however, can be a deterrent. Corn gluten meal, a byproduct of the processing of corn, is a natural product that can kill the seedlings of broadleaf plants in lawn grass or among established plants.
In the mid-1980s, Iowa State University researcher Nick Christians accidentally discovered corn gluten's herbicidal properties while using cornmeal to study a fungus that attacks golf course turf. He did a study on its effect on 22 different weeds. Though the gluten reduced survival rate of all 22, it worked best at killing black nightshade, lambsquarters, creeping bentgrass, curly dock, purslane and redroot pigweed. He also found that the corn gluten meal contains 10% nitrogen by weight, making it a significant fertilizer as well.
Corn gluten meal is a waste product of the process that produces corn syrup and corn starch that is fed to pigs, chickens, cows, cats and other animals. It is available as a yellow powder or brown pellets and is registered as a "minimum risk" pesticide by the Environmental Protection Agency.
Corn gluten acts by inhibiting the growth of the roots of seedlings, causing them to die by dehydration when the soil dries out. It acts on sprouting plants but does not affect more established ones. In fact, due to its nitrogen content, it causes larger plants to grow more vigorously.
Corn gluten can be applied to lawns with a fertilizer spreader at the rate of 12 to 20 pounds per 1,000 square feet. Because it acts as an herbicide on small seedlings, the application needs to be timed at their emergence to be effective. It also requires a period of dry weather after application to kill the root-damaged sprouts. In spring, this is said to be about the time when forsythia blooms and in fall, an application is suggested for lawns between mid-August and mid-September. In flower beds and among shrubs, it is raked into the soil and then watered. The soil should dry for several days after that.
High cost is one of the main drawbacks to using corn gluten. It is more expensive to apply at the recommended strength than chemical herbicides; however, some people feel that the advantages of safety and added nitrogen are worth the expense. In areas with rainy spring weather it may be difficult to find a spell of dry weather during the recommended application period. For home gardeners, it may be best to experiment with small areas first.