Before I explain corn gluten further, you need to understand the difference between the terms "post-emergent" and "pre-emergent" in weed control.
Post-emergent controls work after weeds have germinated. By employing often-misunderstood "pre-emergent" weed control, you're simply attempting to cut weeds off at the pass, before the seeds germinate and begin to emerge from the soil. Primarily marketed by the traditional lawn-care community as weapons against crabgrass, synthetic pre-emergent weed controls are cocktails of chemicals that create barriers at the soil surface through which seeds cannot come to life. The products are powerful, but nonetheless often fail because their use requires proper timing of application and patience. By their nature, these products do not break down quickly in the soil and are therefore among the most controversial lawn care herbicides.
In the natural organic lawn care community, the only pre-emergent control of note is based on corn gluten meal, a protein-rich byproduct of the cornmeal milling process. Marketed under a variety of brand names, corn gluten was patented for use with weeds by Iowa State University in 1991. As the corn gluten dissolves, it also creates a weed barrier, but the results, frankly, have been mixed. Natural turf care professionals use corn gluten effectively because they understand the issue of timing; the product must be on the ground two to three weeks prior to the expected germination of the target weed. For crabgrass in the North, that date can vary from early April to early May -- whenever the forsythia and daffodils begin to bloom. That means that it's already getting a bit late to use corn gluten products as crabgrass control this season.
Potential corn gluten users must be aware of four key points:
1) the product inhibits seed germination of all types and therefore cannot be used within six weeks of overseeding your lawn. That means that in any given spring or fall you will usually not opt to apply corn gluten and overseed with new grass seed;
2) corn gluten does absolutely no good combating previously established perennial weeds, or annual weeds that are already growing;
3) researchers at Iowa State admit that, on average, corn gluten is only about 65 percent as effective as synthetic pre-emergent weed controls;
4) corn gluten is an excellent source of the macronutrient nitrogen and, if used, needs to be factored into your lawn's overall fertilization program for the year. A 40-pound bag of corn gluten will generally contain 8- to 10-percent nitrogen, or between three or four pounds per bag. For some natural lawn-care professionals, the nitrogen included in a spring application of corn gluten is often the only nitrogen they apply on customers' lawns all season.
One newer fertilizer manufacturer in the marketplace, in fact, markets corn gluten meal strictly as a lawn fertilizer. Bradfield Organics' product known as "Luscious Lawn" lists 9 percent nitrogen in its analysis, but doesn't tout any weed 'n feed properties.
"Our concern is that a lot of customers would have unrealistic expectations about this product for use in weed control," said Bill Sadler, the director of product development for Bradfield Organics, a subsidiary of Ralston-Purina in St. Louis, Mo. "We do tell people not to put down corn gluten at the same time they're applying grass seed, but in general we have found that corn gluten is only marginally effective as a weed control. On the other hand, we think corn gluten is a great source of organic nitrogen and we've had great results in our lawn tests and great feedback from customers."
The bottom line tip for the week is to go ahead and use corn gluten as a fertilizer, but don't expect great results on weed control, especially since many annual weeds have already germinated this year. Experiment with corn gluten as a weed control in the future before you make it the backbone of your weed control program.
For more on natural lawn care each week, click on www.safelawns.org.
-Paul Tukey: May 10, 2006.
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