Fertilizer-herbicide: corn gluten efficiency against weeds

One of the most important breakthroughs in organic lawn care was discovered by accident. Researchers at Iowa State University were using corn gluten meal (CGM) to grow a fungus for a study of lawn diseases in newly established golf greens.  

To their surprise, they noticed that no grass seed germinated wherever they put down CGM. 

When they looked at it more closely, while trying to figure out why their seeds didn’t germinate, they concluded that CGM had a naturally occurring protein that suppressed the root formation of germinating seeds. 

And it did not affect existing grass. In fact, at 10% nitrogen, it turned out to be a great organic fertilizer. Once broadcast on a lawn, it was an ideal natural weed & feed fertilizer that did not contain any synthetic fertilizers or pesticides. 

 

What is corn gluten meal? 

CGM is a powdery by-product of the corn milling process. 

The corn kernel has four main parts: 

• Hull, also called fibre, which is the outer skin
• Germ, which is the part containing oil
• Gluten, known for its high protein content
• Starch, the carbohydrate part of the kernel

This process involves isolating the germ and hull fibres, then the remaining starch and gluten are finally separated. 

The gluten part is what is used in animal food. Because it has a high 60% protein content and is extremely digestible, CGM has always been used as an ingredient in hog feed and in pet food.

 

Not really gluten

Confusing sometimes: there is no gluten in corn gluten meal. By the name of the product, you would think that corn gluten meal contains gluten, when in fact, it is 100% gluten-free. It’s a misnomer. 

So, how did the word creep in? The story goes back to the early 1900s, when corn processors called everything that had protein in it “gluten”. Today, some animal food processors would like to see the name officially changed to something more accurate and to avoid any confusion on the part of consumers. 

 

How does corn gluten meal work?

CGM has a natural plant protein that stops root growth when seeds germinate, causing the seedlings to die. 

The seeds will germinate and usually form a shoot, but with CGM, they cannot form a root. CGM does not kill existing weeds, but it will suppress new seeds from forming. It also keeps crabgrass from getting established. 

Over time, the lawn keeps getting thicker every year from the fertilizer part, by squeezing existing weeds out. The inhibitor part keeps weed seeds from starting. In the end, you get a greener, thicker lawn with few weeds.

 

When to spread corn gluten?

CGM works best if watered after application, which helps to break the granules back to powder. This powder forms a roadblock for seeds that may be present in bare or thin spots. Apply on a dry lawn, when the forecast announces two days with no rain, but water immediately after spreading. The idea is to wet the lawn once you’ve applied the product, then let it dry for 2 days.

In short, apply on a dry lawn, water immediately afterwards, and then let it dry for two days.

 

Which weeds are sensitive to corn gluten?

Among the weeds controlled according to the University of Guelph, with this pre-emergent application, if applied correctly and at the right time:

• dandelion 
• white clover 
• Canada thistle 
• crabgrass 
• catchweed bedstraw 
• curly dock 
• purslane
• redroot pigweed
• giant foxtail
  
   

Corn gluten meal products for lawns and gardens

As a by-product, it comes out of the milling process as a fine powder. However, this is much too dusty to use outside. To overcome the dustiness, most corn gluten products available for lawns and gardens are pelletized, like you might see in animal feed. 

Pelletizing typically refers to an extrusion process, where cylindrical pellets are formed by forcing material with extreme pressure through a dye. These are quite hard and resist breaking apart with handling.

For the CGM to be effective on lawns and gardens, the pellets need to break down back to powder form right after application on the lawn. Our research has found that these hard pellets did not break down very quickly, and were often still intact later in the season, rendering them less efficient. 

C-I-L developed a water-dispersible granule that returns to powder quickly after watering. The CGM is gently granulated with no compaction compared to the necessary extreme pressure of pelletizing. C-I-L BIO-WEED & FEED benefits from this process, which makes it a product that is both effective and easy to use, allowing you to obtain great results every time.

 

Advantages of water-dispersible corn gluten meal granules:

• readily disperse when moistened 
• work significantly faster than hard-compressed granules 
• more effective inhibition of weed seeds
  
   

University-tested

Conclusion from the study: 

“The granulated corn gluten meal treatment, particularly at the higher rate, showed very effective control of crabgrass, not significantly different from the chemical pesticide, and over 90% control. None of the treatments had significant effects on the existing mature broadleaf weed presence in the plots, though there was a general reduction in weed presence, which may again be attributed to the competitive effects of the fertilized lawn. The corn gluten meal at the higher rate had generally the best effect on lawn performance as rated by colour, quality, uniformity and density over the course of the experiment.”

CGM needs a “perfect storm” to work effectively on weeds: 

• Broadcasting CGM around the germination time of weed seeds
• Applied with a 2-day dry spell afterwards
• Using the correct amount
  
   

How and when to apply

Broadcast the CGM with a fertilizer spreader in a criss-cross pattern. Use 9 kg per 1,000 ft2. CGM will not work until wetted, so moisten it lightly with 0.6 cm (1/4”) of water. 

One application can suppress weeds for 4-6 weeks. 

Apply to established lawns twice a year: 

• Once in the early spring, two weeks before weed seed germination (before tulips go dormant). The spring application timing for crabgrass is around mid-April, and for dandelions, mid-May.
• Once in the late summer or early fall after heat stress has passed. The effects are cumulative. Results improve with repeated use over time. For the fall application, best to broadcast CGM in mid-August to mid-September.

The inhibitory effect of the product to weed seeds generally dissipates in five weeks following application. 

NOTE: Do not apply the product on newly seeded grass as it may inhibit grass seeds from germinating. Wait until after the first mowing when root systems are established. 

PRO TIP:CGM can also be used in the vegetable garden. Not to be used when sowing seeds, as this would prevent them from germinating. It is extremely useful in the garden with transplants. Some gardeners put down a band of CGM, work it into the upper inch layer of soil and then transplant.