Use Corn Gluten Meal to Kill Lawn Weeds

Corn Gluten Meal (CGM), a by-product of corn milling, is one of the few organic herbicides used in organic lawn care. As a bonus, it’s also a great organic fertilizer due to its high nitrogen content.

There are few organic ways of effectively controlling weeds: homemade remedies like salted water, white vinegar, and citrus oils, all intended for weeds already growing. But there’s only one organic pre-emergent treatment known and that is Corn Gluten Meal (a pre-emergent herbicide is one that keeps the weed seed from germinating properly).

The active ingredient [in Corn Gluten Meal] is a protein found in corn kernels. It is not harmful to humans, to other non-target organisms, or to the environment. Furthermore, it provides a safer alternative to toxic chemicals commonly used for weed control on lawns.

EPA Corn Gluten Meal fact sheet (download pdf here)

What is corn gluten meal?

Corn Gluten Meal is a by-product of commercial corn milling and its active ingredient is a protein. Because of its protein content, CGM is commonly added to livestock feed and pet food. A secondary benefit is that it contains 10% nitrogen by weight, which makes CGM an excellent lawn fertilizer as well.

CGM doesn’t work the same way as a chemical herbicide like Roundup. Chemical herbicides work selectively on targeted plants while leaving others intact. In general terms, a chemical herbicide enters via the leaves, stems or roots of the target plant and the active ingredient moves on to the plant’s cells, disrupting growth and ultimately causing the plant to die.

Corn Gluten Meal interferes with a weed seed’s root development, so the seed never becomes a weed. It’s not selective about which seeds it smothers so it’s imperative that CGM is applied at the right time of the season, so you don’t inadvertently destroy new grass seed.

You won’t see immediate results from CGM, as it’s incapable of killing growing weeds. But annual weeds in your lawn re-seed late in the summer before dying off in the fall and that’s the time for a second application. It takes a few seasons to get weeds under control with Corn Gluten Meal, but if you’re stopping weeds from developing in the first place, there will be fewer weed seeds to treat each year.

When to apply corn gluten meal to your lawn

Apply [Corn Gluten Meal] in late March to mid-April, at least three to five weeks before the crabgrass seeds germinate. Spread it evenly over the lawn… and water it lightly into the soil. After watering, let the soil dry out somewhat so that the sprouted weed seedlings dry up and die. CGM can also be applied in mid-August to control late-season annual weeds.

Besides its high protein content, CGM also contains 10 percent nitrogen by volume, making it an excellent, natural, slow-release fertilizer for lawns. It promotes thicker lawns resulting in fewer places for weeds to become established.

Iowa State University Extension

As Iowa State University recommends, the time to apply Corn Gluten Meal is in spring around Easter before weed seeds germinate, and again in mid-August to suppress late season weed seeds.

Check your weather forecast before applying CGM, as it needs at least a few days of dry weather to go to work after the initial light watering-in. Constant moisture like rainfall on your lawn interferes with Corn Gluten Meal’s action, as the active ingredient has a drying effect on the seeds an germinated seedlings.

CGM can be used in your gardens as well, but make sure you’re not applying it to any areas where flowers or herbs are re-seeding, or transplants have not taken hold yet, as it may interfere with young root development.

For more info see the Corn Gluten Meal research page from Iowa State University, Department of Horticulture.