Corn Gluten Meal – Does it Work For Weeds?

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Robert Pavlis

Corn gluten meal is the new herbicide for lawns. The movement away from synthetic chemical herbicides has left a gap for managing lawns and researchers are scrambling to find an organic solution. One product that is showing promise is corn gluten meal. Its proponents claim that it prevents weed seed from germinating, and if seeds don’t germinate you have a weed free lawn. Sounds like a perfect solution.

There are scientific reports, both for and against the product. Anecdotal evidence from gardeners is also mixed. Does the product work? How should it be used? Are people using it correctly?

lawn and corn gluten meal
lawn and corn gluten meal

What is Corn Gluten Meal?

In the 1990s, Dr. Nick Christians at Iowa State University was doing some work on golf putting greens and stumbled upon the herbicidal qualities of a product called corn gluten meal. This natural material is a by-product of the wet milling process used to produce corn starch and corn syrup from corn.

Corn gluten meal is 60% protein and contains 10% nitrogen, by weight.

Corn gluten meal is not the corn meal found in grocery stores, as so many sites on social media claim. Corn meal has no herbicidal properties and as far as I can tell the only thing it will do in the garden is feed ants and slugs.

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Not All Corn Gluten Meal is The Same

There are different qualities of corn gluten meal and the one that is a herbicide contains 60% protein. This product is always labeled as a pre-emergent herbicide.

The true corn gluten meal herbicide is expensive and so many people have tried a cheaper product called corn gluten feed, or distillers grain. These animal feed products may even be called corn gluten meal but they will not be labeled as a pre-emergent herbicide.

One reason corn gluten meal may be getting bad press is that gardeners are trying to use the feed products and then reporting they don’t work. They don’t work because they don’t have a high enough protein level – they are the wrong product.

Another common problem is that corn gluten meal needs to be applied at a heavy rate of 20 pounds per 1,000 sq ft and most home spreaders can’t reach this level. If it is not applied thick enough, it won’t be effective.

Does it Prevent Seeds From Germinating?

Many sites report that corn gluten meal prevents seeds from germinating, but this is a myth.

After treatment with corn gluten meal, seeds will germinate normally, by producing a radicle (aka root). The food for growing the radicle comes from inside the seed and is unaffected by its new environment. Once the radicle is formed it starts to make roots which absorb water and nutrients from the soil. Corn gluten meal inhibits the formation of roots – it does not prevent seed germination.

The death of the seedling depends on a perfect storm of events. The developing roots need to absorb enough protein from the corn gluten meal to have an effect. This is why higher application rates generally result in higher weed control. The roots also need to be on the dry side after germination. Too much water dilutes the effect of the protein and roots keep growing. As discussed below, application of the product is critical.

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If corn gluten meal stops root growth, why does it not affect mature plants?

Mature plants have many more roots and they have roots that are located deeper in the soil. They are never exposed to enough protein to have a significant effect. Corn gluten meal does not harm existing plants, even if they are weeds.

Corn Gluten Meal – Does it Work?

Dr. Nick Christians’ original field work showed that corn gluten meal applied at 99, 198, 297, 396, 495, and 594 g/m2 reduced crab grass infestation by 50, 65, 80, 95, and 93%, respectively when applied 1 week before crab grass germination. Applying it 4 weeks before germination required higher amounts to have the same effect.

When 22 different weeds were tested they found that all were reduced, but the degree of reduction varied by both species and application rate. At low rates some weeds were unaffected. Since this work was done, other research has identified a few weeds that seem to be immune to corn gluten meal.

Most discussions refer to weeds, but non-weed seeds like grass, perennials and vegetables are also affected.

Others have also tested corn gluten meal. A study out of Oregon State University says that they could not replicate the initial field findings. I am not sure that this work was ever published? The work was part of a Masters degree and is available as a Thesis. It found that corn gluten meal did not reduce the number of weeds. In it’s conclusion it states that this could be due to the fact that the testing was done on clear soil, with no grass and therefore no competition, or that it might be due to an old product. The product was not tested in the lab to verify it worked. The work did not record rain fall during the tests and Oregon can be quite wet, so it is also possible that excess rain kept the product from working.

The University of Guelph Turf Grass Institute has researched corn gluten meal and concluded that the product does control weed seed germination but that it was not 100% effective.

Dave Gardner from Ohio State University made a video showing his results. He found that to be effective you needed to use twice the recommended amount of 20 lbs/1,000 sqft, which makes application very expensive. He also commented that you need to apply it for at least two years since “first year results are disappointing.”

You can find both positive and negative research for this product. The key might well be in using good quality product and using it correctly. Any research that does not provide rain data is not of much help since a dry period after application is required for the product to work.

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Too Much Nitrogen

Corn gluten meal contains about 10% nitrogen by weight in an organic form, mostly protein. The nitrogen is slowly released into the soil as it decomposes over a 3-4 month period.

This is an important fact since this nitrogen makes both turf grass and existing weeds grow better. It is actually a good, but expensive, lawn fertilizer.

Any weed seed that is not stopped, will be able to use the extra nitrogen to grow faster than if would in an untreated lawn. This can be a big problem if you apply it at the wrong time.

This points out one of the serious limitations of anecdotal reports. Almost none of these count actual weeds, so it is quite possible that people conclude the product did not work because it produced nice large weeds which cover a large area of the grass. The overall appearance of weeds was not reduced.

Is It Safe for Grass?

Corn gluten meal will not harm any existing type of lawn grass or other perennials. It should not be used at the same time as seeding a new lawn.

When and How Should It Be Applied?

Corn gluten meal needs to be applied just before weed seeds start to germinate. Most weed seed germinates in spring, with a second flush happening in fall. For crab grass control, it is recommended that you apply it when the forsythias start to bloom.

There are two problems with this advice; different weed species germinate at different times and germination is affected by the environmental conditions, which change from year to year. So it is tricky to apply it at the right time. Apply too late and the nitrogen feeds the already germinated seed. Apply too early and it has limited effect.

A rate of 20 pounds per 1,000 sq ft reduced crab grass by 60%. Higher rates should be more effective, but they will also cost much more. You can get 90% control, but the cost does not warrant the results.

Water it in right after application.

The next step is critical. It must remain dry for 7 days after it is applied. If you get too much rain, the excess water will reduce the herbicidal qualities of the product and you will see no weed reduction. How well do you trust the weatherperson?

Corn gluten meal will remain effective in soil for up to 6 weeks provided that it stays dry enough to prevent microbes from decomposing it.

More Corn Gluten Meal Myths

Alters pH

Corn gluten meal will not alter the pH of the soil to any significant amount.

Effective on All Weed Seed

It is effective on most types of seed, but not all.

Works by Drying the Seedlings

Many sites make the incorrect claim that corn gluten meal dries out the seedling. This is not correct. It has been shown that Alaninyl-alanine and 4 other dipeptides cause roots to stop their development.

Can be Used All Summer

Ads for product and some gardening sites recommend that the product can be used all summer long. It is true that it can be used all summer long, but few weed seeds germinate in summer. Using the product in summer, unless you are trying to get rid of summer germinating weeds, is a waste of money.

It Is Natural and Safe

Since this is a natural product everyone assumes it can be used without risk, but that is not quite true. Corn and corn by-products such as this are known to cause allergies in some people and this condition can be serious. If you or your family suffer from respiratory or hypersensitivity due to corn, avoid exposure to corn gluten meal.

Should You Use Corn Gluten Meal?

The product works but is not 100% effective. It must be used correctly or it won’t work. If you are located in an area which is particularly wet in spring, it is probably not going to work.

If your lawn has a lot of existing perennial weeds, the nitrogen in corn gluten meal will make them grow better and make the lawn worse. Deal with the perennial weeds first.

Corn gluten meal has become very expensive and to be effective it needs to be applied thickly. If you do use it, don’t skimp on the application.

This is a good product to try if you have a lot of crab grass (it is an annual), live in an area with a dry spring and you are not allowed to use, or don’t want to use synthetic herbicides.

References:

1) Corn Gluten Meal Research; https://www.hort.iastate.edu/horticulture-research/corn-gluten-meal-research/

 

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

32 thoughts on “Corn Gluten Meal – Does it Work For Weeds?”

  1. I’m at my 3rd years of trying to eradicate Poa Annua… I apply liquid form at 25% concentration, in 1 gallon sprayer on 1000 SQFT, starting mid March to mid April and mid September to mid October. I make an application every 2 week. I have some success and see good reductions of lime green patches but hardly completely eradicate. Any advice ?

    Reply
  2. Had some corn gluten meal that spilled in my gravel drive in the fall. In the spring, that area was weed-free, which was a first in many years for that area!

    Reply
  3. Has corn gluten worked for you. I would really like to try it, but do not know much about it. I would rather the advice of someone who has tried it.

    Reply
  4. I’ve used corn gluten for years with great success (better than 95%).
    A caution; expect optimal results the 2nd year. Corn gluten remains active for about three months so timing is everything. Apply at least twice a year starting in early spring. The 2nd year should see a marked reduction in weeds that can be spot treated. Last year I purchased it in bulk 50lb bags from the following link:
    https://www.7springsfarm.com/products/corn-gluten-meal-granular-9-0-0-50-lb-bag

    Reply
    • “great success (better than 95%)” -how did you measure that?

      “expect optimal results the 2nd year” – it does not work the second year. Even you say it only remains active for 3 months. – I don’t think it is even that long.

      You want to apply when seeds are germinating.

      Reply
      • I may be off on the 95%– in reality it may have been a greater percentage. My grass was Full of weeds, perennials were spot treated so any seeds blown in were affected by the gluten. Annual weed seeds failed to grow. I have approximately 4,000 SFT of grass, so when, after two years I may of had a few dozen a year to spot treat, yes, I’d say at least a 95% reduction. I live in Nassau County, Long Island.

        Reply
      • I’ve used Corn Gluten Meal for going on 5 years now and my lawn is thicker and greener that it ever was and I’ve lived here over 15 years, we have a clay soil and its somewhat dry in the summers but using it as a fertilizer I’ve not found anything better!

        Reply
  5. Decades ago I found out about the issue with flower and vegetable seeds not germinating AFTER I had put a 40lb bag of cat litter made with corn cobs on 4 beds around the outside of my house. My cat didn’t like the litter…so I had it to throw it out so I thought why not add it to my beds that desperately needed something to help the sandy soil. Then months later…in spring I keep seeding the beds…and it was a failure…flowers and veggies. I also noticed my prolific chickweed that just flourished in those beds was sparse to none at all. It was so odd and just kept happening all spring that I did some research and found the original info about corn gluten found to be pre-emergence inhibitor. I think Preen was out but I had never used it…and didn’t know it was made of corn. BUT…the brand of cat litter I used worked GREAT…and seemed to last a very long time. I couldn’t direct seed at all for 2 years in those beds. I am sure I put way more than the Preen would have been applied…but I was using it to put organic matter in my soil AND to not waste unused cat litter.

    Reply
  6. Corn gluten Applied under thick newspaper or cardboard on garden paths or in beds worked beautifully.
    Having used thick newspaper for years without corn gluten and then with corn gluten — I feel that I have done a controlled study ! ( smile )

    Reply
  7. I find elm seeds germinate like crazy. they are easy to pull but there are always HUNDREDS of little seedlings, making the process time consuming.

    Would applying corn gluten meal just as seeding season approaches be helpful or just a huge waste of money?

    Reply

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