Corn gluten meal is a great fertilizer — but its value as a weed control product is marginal.
Due to the Ontario Pesticide Ban, there has been an increased demand for organic weed control products and 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 effectively as its chemical counterparts.
In my opinion, corn gluten meal has been vastly oversold by an overeager industry and with the prices of corn gluten meal rising in the past several years, homeowners can go broke trying to buy enough product to really make a difference in their weed population. This doesn’t mean that corn gluten meal doesn’t have any value in lawn care or gardening.
The development of the corn bi-product and patented by Iowa State University in 1991 as a pre-emergent lawn herbicide. This product is touted to kill 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 lbs. 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 does not 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 the problems about over-selling of corn gluten meal is that the companies market the product as a pre-emergent control 52 weeks a year. 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 the late winter and early spring depending on the climate. The general rule of thumb is to apply corn gluten meal just as the forsythia plants break into bloom. If you apply this product 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.
Since commodity markets have been very volatile since 2007, the price has at least quadrupled in the past few years. The lawn care companies who rely on corn gluten meal for their weed control can’t possibly compete on price with consumers’ knowledge of pricing in the chemical weed-control industry pre-2009.
CORN GLUTEN MEAL’S UPSIDE:
This product makes an amazing fertilizer which makes sense because corn and grass are from the same plant family. Corn gluten meal gives the lawn a nice, natural dark green hue and 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 great product. Also, if you’re just using it as an organic fertilizer, you can reduce the rate to 10 lbs. per 1,000 square feet and still get substantial value.
Corn gluten meal contains 10% nitrogen by weight and by recycling your grass clippings back into the lawn and allowing 5-10% clover to grow in the lawn, you’re getting more than enough nitrogen for the entire season. AND if you happen to apply at 20 lbs. per 1,000 square feed right now, just as the forsythias are about to bloom, you will get some weed control — Just don’t set your expectations too high.
SO WHAT ABOUT WEED CONTROL?
If your lawn is mostly weeds, it’s because your soil wants to grow weeds and not grass. The best way to manage weeds on the lawn is to change the soil conditions so the soil wants to grow grass by incorporating organic matter/compost into your lawn, over-seeding on a regular basis as weeds don’t like competition with grass for their ‘turf’ and fertilize on a spring/fall basis to keep the grasses ahead of the weeds.
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) over-seeding whenever thin or bare spots appear on the lawn; 4) pulling or spot treating weeds with an organic herbicide or iron-based selective herbicide when necessary.