“What is your opinion of using Cornmeal Gluten to prevent weeds starting from seeds?” Question from Kathy of Loomis, California
Answer: Corn gluten is a popular all-natural pre-emergent herbicide that will stop the germination of certain seedlings when properly applied. That means that it keeps weed seeds from sprouting. For this reason, it is important to apply it well before cool-season weed seeds get going in late winter and spring and warm-season weed seeds get going in summer.
Corn gluten is an all-natural byproduct of the corn industry. Essentially, it is comprised of corn protein. For this reason, it is not harmful to people or wildlife, while stopping some weed seeds from sprouting. With that said, there are some different opinions and studies with varying reports on its efficacy. Here are the two sides.
Corn Gluten As a Pre-Emergent Herbicide
A 1990s Iowa State University study showed that corn gluten was an effective pre-emergent herbicide for some weeds. They found that it was most effective in stopping weedy grasses, such as crabgrass, as well as some broadleaf weeds, such as chickweed and dandelions. Corn gluten also contains 10% nitrogen, so it helps feed plants as well.
Corn Gluten’s Herbicidal Short-Falls
Some studies show corn gluten, when not properly applied at the right time, can feed weeds due to its high nitrogen content. That’s because it does not negatively impact emerged weeds, so these will need to be hoed out or hand-weeded before applying any pre-emergent. It is also important to note that corn gluten does not work on all weed seeds. A Washington State Univerisity overview of corn gluten states: “Corn gluten meal is not a selective product, nor is it effective on all weed types. Several species of weeds, flowers, and vegetables are inhibited by corn gluten meal, while others are not. Effectiveness in greenhouse trials generally increases with [the] application rate (as does the cost).”
As for me, I rarely apply pre-emergents. This is because I favor various mulches and hand weeding to stop weeds in my gardens. For me, these are the two best methods to keep weeds away. Here is an article along these lines.
I hope that this helps!
Black Gold Horticulturist