Corn gluten meal (CGM) is a natural substitute for synthetic pre-emergence herbicides. Pre-emergence herbicides attack seeds before the seedlings emerge from the soil. CGM is a by-product of commercial corn milling that contains the protein fraction of the corn (60%). Its use poses no health risk to people or animals. In addition, corn gluten meal is 10% nitrogen, by weight.
CGM is effective only against seeds, not existing plants. Annual weeds will die on their own by the end of autumn. But most of the seeds they produce later in the season shouldn’t sprout – provided you’ve applied the CGM properly and at the correct time. The same goes for perennial weeds.
Apply corn gluten meal first in late April/early May, then a second time around mid-August. Spread the product evenly, at a rate of twenty pounds per 1,000 square feet of lawn — use a fertilizer spreader if you have one. Water it lightly into the soil in order to activate it. The CGM should remain effective for five to six weeks each time you apply it. Applying Corn Gluten Meal at this rate, twice a year, will provide your lawn with four pounds of nitrogen fertilizer annually, more than enough to meet its needs.
CGM does not give instant results; but each year, weed control will improve. Keep in mind that CGM prevents most seeds from sprouting, so use it only on lawns and beds that you do not plan to seed into.
Adapted from the University of Minnesota Extension Office Website. http://www.extension.umn.edu/