Natural weed product is costly, often ineffective

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With lawn season here, scarcely any subject will spur more discussion than corn gluten meal, the corn byproduct 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 chemical weed controls 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 …

Some background

Corn gluten meal 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 weeds’ 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 grow 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 that begins right now here in Maine. The general rule of thumb is to apply the corn gluten just as the forsythia plants break into bloom. When applied before or after that time, the product essentially has little value for weed control.

The cost

The price of corn gluten meal has at least quadrupled in the past three years to approximately $1 per pound retail. 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 Maine 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. 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 heck 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, The Organic Lawn Care Manual, 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

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 GardensAlive: For goodness sake, don’t use the chemicals … no matter what!

Paul Tukey is the founder of and the producer of the movie A Chemical Reaction ( He can be reached at [email protected]

The natural weed control corn gluten meal must be applied at high rates and at the perfect time to be effective. (Contributed photo)