Since the 1990's, corn gluten meal (CGM) has taken the gardening world by storm. CGM is the protein by-product of milling corn, and this high-nitrogen compound was discovered by researchers at Iowa State University to be an effective pre-emergent herbicide, reducing seed germination by inhibiting root development. Organic gardening and farming communities have quickly adopted this natural miracle substance as a method of weed control.
There are many lessons in the continuing saga of CGM. I've seen the step from laboratory efficacy to field efficacy fail often in pharmaceutical trials and surgical procedure trials in my chosen profession of veterinary medicine. There are a couple of hidden messages here to gardeners as well, though: First, organic gardening principles are great in theory, but it's obvious that weeding is so much of a chore that even organic gardeners will seize on any chance to reduce the work involved. So just who is kidding who? Second, just because a substance is natural does not mean it's a miracle cure or that it is economical to use. We're going to be driving the price of corn high enough with all our driving around on the ethanol we derive from corn; we shouldn't throw our gardening budgets out of whack by using up even more corn as a partially-effective pre-emergent herbicide. And if it is not useful as a herbicide, but we use it anyway as an organic fertilizer, somebody out there had better be doing some calculation on whether we use more inorganic fertilizer on Iowa and other Midwestern fields to grow the corn for a bag of CGM than the bag of CGM provides us back as organic fertilizer. As the grandson of Indiana crop farmers, I guarantee you that no dirt farmer is growing 200 bushel/acre field corn without artificial nitrogen and herbicides. Is CGM really "organic" or is it organized hype?