Cornmeal

Sprinkle cornmeal in the garden to stop weed seeds from germinating! 

​Cornmeal prevents fungal diseases, too! 

Wouldn’t that be convenient?

Cornmeal (Popo le Chien) CC BY-SA 3.0

Like many other garden fantasies, the fallacy about cornmeal originated in fact, but the above claims have not been able to withstand the tests of time and science.

How the cornmeal myth began

In 1985, Dr. Nick Christians, from Iowa State University, found that corn gluten meal, a byproduct of the corn milling process, showed herbicidal effects during a turfgrass experiment. The corn gluten meal was found to desiccate newly forming roots of small-seeded plants in highly controlled greenhouse environments. As such, corn gluten meal can act as a pre-emergent herbicide, an idea that was patented in 1991, but those results have not been repeatable in outdoor environments, such as family gardens.

What is corn gluten meal?

Corn gluten meal is not the same thing as the cornmeal you find at the grocery store. Instead, it is what is leftover after the corn has been ground up to make cornmeal. Corn gluten meal is a byproduct used in livestock and pet food. It is the primary protein found in corn and does not actually contain true gluten. 

Corn gluten meal is not species specific, so it will, when conditions are just right, desiccate any new, small-seeded plant roots, including your lettuce, carrots, and many others. On the other hand, corn gluten meal contains 10% nitrogen, so sprinkling it on your lawn or garden will provide this important nutrient, leading to lush growth and healthier plants, weeds included. [Cornmeal has practically zero nitrogen.]

Cornmeal as fungicide

Popular claims also state that cornmeal will help control fungal diseases, such as brown patch, black spot, and dollar spot. That’s strikes me as funny, because cornmeal agar is produced as a medium specifically designed to grow fungi for laboratory work! 

Finally, for the record, ants do not “explode” or die in any other fashion when they eat corn gluten meal, cornmeal, or other foodstuffs. In fact, ants, rats, squirrels, and many other garden pests love cornmeal and corn gluten meal, so choose your battles wisely.

If you want to get rid of weeds, cut them off at ground level before they go to seed, and apply a thick layer of mulch.

Now you know.