Corn Gluten Meal as Weed Control?: 20 Years Later, the Jury is Still Out
Scarcely any subject in organic lawn care has spurred more discussion in the past two decades than corn gluten meal, the corn bi-product that was patented by Iowa State University in 1991 for its pre-emergent weed control properties. In the past decade, as the demand for alternatives to toxic chemicals has risen, the use of corn gluten meal on lawns has grown exponentially. In many cases, though, so has the frustration of consumers who expect the corn gluten meal to work as efficiently as its chemical counterparts.
My standing answer to anyone who asks about this natural weed alternative is that corn gluten meal has been vastly oversold by an overeager industry. With the rising prices of corn gluten meal in the past three years, homeowners can go broke trying to buy enough product to really make a difference in their weed population.
That does not mean, however, that the product has no value in lawn care or gardening . . .
Dr. Nick Christians, one of the most widely respected figures in the lawn care industry, is credited with developing corn gluten meal as a pre-emergent lawn herbicide. His product kills the dicot weeds (clover, plantain, dandelions etc.) before they grow to adult size. The weed seeds actually do germinate, but the corn gluten meal inhibits the expansion of the plants’ roots and they quickly die of dehydration. So far, so good.
Iowa State’s own research on the subject, however, shows that to achieve anything close to full control requires the application of at least 20 pounds of corn gluten meal per 1,000 square feet — at exactly the right time in the spring — just before the weed seeds germinate. Corn gluten meal doesn’t inhibit weeds that already have root systems; in fact it makes fully formed weeds grown even faster due to the nitrogen content of the product.
MORE ABOUT TIMING
One of my pet peeves about the overselling of corn gluten meal is that the companies market the product as a pre-emergent control 52 weeks a year. And while they’re technically not lying, any gardener knows that the majority of weed seeds — especially the dreaded crabgrass seeds — germinate during a very short window in late winter and early spring depending on the climate. The general rule of thumb is to apply the corn gluten just as the forsythia plants break into bloom in the North, or the dogwoods begin to bloom in the South.
If you apply corn gluten meal anytime before or after that window, the product’s efficacy for weed control falls through the floor. The unsuspecting consumer can get ridiculously frustrated by unfulfilled expectations . . . especially given the price.
For a long time, corn gluten meal was a good deal. Given the volatility of the commodity markets that began in 2007, however, the price has at least quadrupled in the past three years. A quick Google search today reveals just how out of whack the market has become: High Country Gardens sells a 7-pound bag for $21.95: http://www.highcountrygardens.com/catalog/product/H0033/; Amazon is offering a 25-pound bag of Espoma Organic Traditions for $30.95. That’s a better deal per pound. But when you need to apply 20 pounds per 1,000 square feet to achieve decent weed control, you’re still looking at hundreds of dollars of cost for an average 8,000-10,000 square foot American lawn.
That cost factor drives the organic lawn care industry crazy. The companies who rely on corn gluten meal for their weed control can’t possibly compete on price with the chemical industry, which dumps its poisons onto people’s lawns at pennies to the dollar compared to corn gluten meal.
CORN GLUTEN MEAL’S UPSIDE
Having said all of that, I am not completely anti-corn gluten meal. I was impressed by the tactic of one of our former sponsors, Bradfield Organics, which began selling corn gluten meal as a straight fertilizer in 2007 — while not making any claims about the product’s ability to control weeds. In my lawn trials for my book here in Maine, I found corn gluten meal to be an amazing grass fertilizer — which makes sense if you think about it because corn and grass are from the same plant family. Corn gluten meal gives the lawn a nice, natural dark green hue and, at least anecdotally from many folks in the organic lawn industry, seems to provide a large measure of disease resistance.
So, as a once-a-year fertilizer — if you can afford it — on your lawn, it’s a hell of a product. And if you’re just using it as a fertilizer, you can drop the rate to 10 pounds per 1,000 square feet and still get substantial value. Corn gluten meal contains 10 percent nitrogen by weight, so at 10 pounds per thousand, you’re putting down a pound of nitrogen. That, in combination with recycling your grass clippings back into the lawn and allowing 5-10 percent clover to grow in the lawn, will give you more than enough nitrogen for your lawn for the entire season. AND if you happen to apply that 10 pounds per thousand right now in the north, just as the forsythia are about to bloom, you will get some weed control. Just don’t set your expectations too high.
SO WHAT ABOUT WEED CONTROL?
I wrote a whole chapter in my book about weed control that had very little about corn gluten meal, for all the reasons stated above. If your lawn is mostly weeds, it’s because your soil wants to grow weeds and not grass. The sustainable way to manage weeds on the lawn is to change the soil conditions so the soil wants to grow grass. We review this at length in our book and in the how-to videos at http://www.safelawns.org/video.cfm. Other weed control factors include: 1) mowing height, the taller the grass, the fewer the weeds; 2) avoiding raking in spring so weed seeds don’t get stirred up and germinate; 3) overseeding whenever thin or bare spots appear on the lawn; 4) pulling or spot spraying weeds with organic herbicides when necessary. We also have high hopes for the new iron-based selective herbicide, which is now available from our sponsor, GardensAlive: http://www.gardensalive.com/product.asp?pn=3721.
ONE LAST NOTE
Several companies are selling liquid corn gluten as a weed control product. Iowa State University’s research indicates that this liquid hydrolosate does have slightly better weed control efficacy than the granular or pelletized corn gluten meal, but the same cost and timing issues stated above still apply. In other words, buy it with your eyes open.