Stop weeds before they emerge with corn gluten meal

dandelion with seeds blowing
Pre-emergent herbicides can inhibit dandelion seeds and other seeds from germinating, but won’t kill taproots or established plants. Photo by Herbert Goetsch on Unsplash

by Connie Oswald Stofko

Stop weeds before they even pop out of the ground–that’s what pre-emergent herbicides do. Pre-emergent herbicides act on seeds at the germination stage.

Corn gluten meal is an organic pre-emergent herbicide. There are synthetic pre-emergent herbicides, too.

These can work well on grass seed and broad-leaf seeds. However, like every herbicide, they don’t kill every type of weed. They don’t kill existing weeds. And they don’t work on plants with tap roots, such as dandelions.

They may kill seeds that you want, so don’t use a pre-emergent herbicide within a foot or two of an area where you want seeds to grow.

These pre-emergent herbicides “don’t distinguish between weeds and cultivated plants,” said said John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County.

Using pre-emergent herbicides isn’t an issue for transplants, he noted. You can transplant a new perennial into an area where you have spread these products.

Timing is critical when using pre-emergent herbicides.

Timing is critical

forsythia in Buffalo NY area
This is what a forsythia looks like in bloom. Photo by Connie Oswald Stofko.

The optimal time to use pre-emergent herbicides is early in the spring, just before the forsythias bloom or while they are in bloom, Farfaglia said. This is usually at the beginning of April; sometimes earlier and sometimes later. (The forsythias are blooming now in my neighborhood.)

Once the plants pop out of the soil, it’s too late to use pre-emergent herbicides.

Some weeds emerge in early autumn, he said. For those weeds, apply the pre-emergent herbicides in the beginning of September.

Corn gluten meal

Corn gluten meal isn’t the same as corn meal that you have in your pantry; corn meal won’t help with weeds.

Corn gluten meal is derived from corn and is mostly used as a livestock feed ingredient, according to this profile from the New York State Integrated Pest Management Program and Cornell Cooperative Extension.

As a pesticide, corn gluten meal has been shown to inhibit germination of both grassy and broad-leaf weeds. See more specific information on weeds that it controls in the section on herbicidal activity here.

No incidents of adverse incidents to human health, non-target species or the environment have been reported.

Synthetic pre-emergent fertilizers

One synthetic pre-emergent fertilizer is Preen. See a list of weeds that Preen controls here.

Its active ingredient is trifluralin. Trifluralin doesn’t pose adverse effects to humans or the environment, according this fact sheet from the Environmental Protection Agency.

It is practically non-toxic to birds and mammals. However, it can be toxic to fish and other aquatic animals, so you have to make sure it doesn’t get into ponds, creeks or other waterways.

Trifluralin generally is of low acute toxicity, but has been classified as a possible human carcinogen, according to this fact sheet. The main concern is for people who work with it a lot. They can reduce their risk by wearing protective clothing.

The home gardener should also read and follow package directions, Farfaglia said.

“Does Preen worry me if it’s used properly?” Farfaglia said. “No.

“Whether you’re using an organic or synthetic product, the directions for use are important.”

9 Comments on “Stop weeds before they emerge with corn gluten meal

  1. I have purchased corn gluten meal from Urban Roots Garden Center, Buffalo, NY in the past.
    I had very good luck using it.
    Do remember that it is “somewhat” a “preemergent” herbicide, but it acts differently than synthetics.
    You may want to rethink its use if you are contemplating spring overseeding of your lawn. If you apply now, you have to wait at least 6 weeks before over-seeding.
    #DidYouKnow: as corn gluten breaks down, it releases Nitrogen (the first number on fertilizer bags) and will feed your lawn. Its N profile is 10%, and the N will continue to feed for 3-4 months after application.
    *Note: Corn gluten does not prevent weed seeds from germinating. What it does do is to stop (burns) the root growth of nefarious lawn plant seeds, i.e. Crabgrass after they germinate. You want to water it in or pray for rain within 5 days of applying, a 1/4″ of moisture is adequate… we are not doing a full, deep root drench. After that, a dry period for 1 or 2 days is necessary to complete the root kill.
    Should there be rainfall within the 1st wet day forward to the 2-day dry period, the corn gluten becomes fertilizer and not an herbicide. Timing is very important. Check your weather forecast.
    BTW- my Mom, a very talented gardener swore by Preen, especially in her rose and perennial gardens. It does work.
    Remember: Labels are there for you to read. Not once, not twice, but three times to understand how the product works or won’t work.

  2. You can get it on Amazon.
    A local feed store like Thiele’s Country Max might have it too.

  3. Ugh. The weeds have taken over my planting beds. Going to local farm store today. Reposting this article on my facebook.page for my PNW garden buddies to read. Our forsythia are in full bloom in Portland. Oregon. Happy weed free gardening!

  4. I’ve also been told by a woman who grew up on a Farm & used this, that if you have a Rat problem, it will help to kill them. Not exactly sure why this works, but she says that it does. I have not tried this yet because I want to Fertilize my lawn & over-seed it. I will try the Corn Gluten Meal in Fall.

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