How to Use Corn Gluten Meal as a Natural Herbicide to Prevent Weeds

Corn gluten meal is a natural way to thwart weeds and crabgrass in your lawn and garden. It does this by stopping the plants' roots from developing. Success with this method depends on timing. Apply corn gluten meal too late, and weed and crabgrass seeds may have already developed roots, meaning it is too late for the corn gluten meal to be effective. Here, we share everything you need to know about corn gluten meal and how to use it in the garden.

What Is Corn Gluten Meal?

Corn gluten meal is a byproduct of the wet corn-milling process, which is when corn is processed into corn starch, corn gluten feed, steep liquor, and germ oil meal, says Lucie Bradley, a gardening and greenhouse expert at Easy Garden Irrigation. "This makes it a natural product safe to use around children and pets," she says. As an herbicide, it prevents weed seeds from germinating by stopping their root growth.

Corn gluten meal also contains about 10 percent nitrogen by weight, which can be a benefit and a disadvantage. "On the positive side, by containing nitrogen, it acts as a fertilizer," says Bradley. On the negative side, unless you remove all existing weeds before you spread it, the nitrogen will boost the growth of existing weeds, she says.

How Corn Gluten Meal Works

Corn gluten meal works by preventing weed seeds from forming roots after germination. "It’s used to prevent weeds from growing quickly, and allows established grasses to outpace it," says Craig Elworthy, lawn expert and founder of DIY natural lawn care company Lawnbright. "It's a pre-emergent that prevents them from growing in the first place."

But corn gluten meal isn’t an instant solution. "After the first application, you may not notice any difference," Bradley says. "It’s only after you have used it over a couple of seasons that you will start to appreciate that it is working, and it could be up to two to three years of use that you will have managed to reduce your weeds by up to 90 percent." Hence, she recommends using corn gluten meal alongside other forms of weed control for the best results.

When and How Often to Use Corn Gluten Meal

Because corn gluten meal is a pre-emergent herbicide, applying it at the right time is essential. "Although you can research the germination times for certain weeds, I’d advise using corn gluten at the most common times of the year when weed seeds will be germinating," says Bradley.

Applying in spring (late March to mid-April, depending on the weather) should capture many weed seeds as the weather warms, she says. Another good time is in autumn, such as October, says Elworthy. This is when certain seeds from existing weeds will be in the ground, ready to overwinter through the colder months.

How to Use Corn Gluten Meal as an Herbicide 

For the best results, follow these tips from our experts when using corn gluten meal as an herbicide.

1. Remove any weeds already growing: Corn gluten only stops the production of roots on sprouting seeds, says Bradley. Any weeds that already have roots will not be affected by applying corn gluten meal, and must be removed using other methods, such as hand-pulling.
2. Rake the lawn or area of application: Rake the lawn to help break up the soil surface, making it easier for the granules of corn gluten meal to dissolve and start to inhibit root growth.
3. Apply the right amount: Bradley recommends applying 20 pounds per 1,000 square feet. "Any less than this, and it won’t be effective," she says. Use more, and the nitrogen in the corn gluten will accelerate existing weed growth.
4. Water the application site: Water helps the corn gluten meal dissolve into the soil. Water by hand immediately after application using a watering can, hosepipe, or sprinklers, says Bradley. Wait too long to water, and this herbicide is ineffective.