Corn gluten meal products have been used as herbicides for over 30 years, but there’s still a lot of controversy around them. Does corn gluten meal work on weeds? How does it prevent weed growth? What results should one expect from it? Is it worth using?
Since it’s a natural product, healthier for the environment, soil, and crops than the synthetic alternative, it’s worth the debate. If you’re considering using it on your lawn or garden, read this article. We included all the information you need to decide if corn gluten meal is a suitable herbicide for you or not.
- What makes corn gluten meal a weed killer?
- Types of corn gluten meal products and herbicides
- Does CGM work on all types of weeds?
- How to use corn gluten meal as a herbicide
- How effectively does corn gluten meal kill weeds?
- Where to buy corn gluten meal and how much it costs
- The fertilizer side of CGM
- Pros and cons of using corn gluten meal
- Natural weed control alternatives to CGM
What makes corn gluten meal a weed killer?
Corn gluten meal (CGM for short) is a by-product of the corn milling process containing 60 to 65% protein. This high protein content makes it an excellent option as animal feed and also gives it herbicidal properties.
In the soil, CGM’s protein breaks down into dipeptides that inhibit root development in the seed germination stage.
Historically corn gluten meal has been used as a valuable protein source for feeding livestock and, more recently, for making pet food. Its weed-killer abilities were discovered by accident in 1986 at Iowa State University by Dr. Nick Christians and his research team.
They were studying a fungal pathogen of golf course turf and using CGM as a growing environment when they noticed their test grass seeds didn’t germinate as expected.
How does corn gluten work on weeds? Studies indicate that CGM prevents weed seedlings from growing roots. CGM action is not selective, and it’s time-limited. It stops all sprouts from rooting – weeds, grass, and veggies alike – and only acts during that narrow window of time when plants form their first roots.
With these properties in mind, corn gluten meal was patented as a weed killer in 1991. By 1997 over 15 manufacturers were producing and selling it across the U.S.
Types of corn gluten meal products and herbicides
Various products based on corn are often confused with the corn gluten meal that kills weeds. Make sure you’re getting the right kind of product, or it won’t work on weeds.
Corn meal is the food-grade product people use as flour in muffins and pancake recipes or to coat chicken thighs, fish, or meat before throwing them into the frying pan. It only has 8% to 9% protein content, too low to be effective as a herbicide.
Corn gluten feed (CGF) is a by-product of wet milling corn obtained by producing corn starch, corn syrup, or corn oil. Highly available in the South, CGF is low in starch but rich in protein and fiber, making it a popular food source for cattle, sheep, goats, horses, and other farm animals. CGF has an average protein content of 23.5% and is not the herbicide form of corn gluten.
Corn gluten meal is also a secondary product of corn processing, but it’s much richer in protein, with a 60% to 65% protein content. This is the one to use as a herbicide. You’ll also find products labeled as “corn gluten meal” meant for feeding animals. Avoid them, and look for corn gluten meal specifically labeled as a herbicide or pre-emergent weed killer.
Does CGM work on all types of weeds?
Corn gluten meal effectively controls most common lawn weed types but to different degrees.
Grassy vs. broadleaf weeds
Unlike post-emergent contact herbicides, CGM’s effectiveness doesn’t depend on the contact surface’s size. Corn gluten meal damages roots emerging from the seed, so it’s effective on grassy and broadleaf weeds alike.
It’s typically used for crabgrass prevention, but it also works on smartweed, dandelions, redroot pigweed, lambsquarters, purslane, common Bermudagrass, and invasive creeping bentgrass.
Annual vs. perennial weeds
Corn gluten meal is the most effective on annual weeds because they propagate only through seeds. Attacking the weeds in their germination stage, CGM is the perfect solution to prevent annual weeds in gardens and lawns.
With perennial weeds, it is less effective but still useful. Perennials regrow from their established roots and spread through seeds vulnerable to corn gluten meal. You’ll need to remove the already-grown perennials differently, but you can use CGM to limit the germination of a new generation of perennials.
What’s the difference between perennial and annual weeds? Annuals only live for one growing season and then die off, while perennials can live for several years. That’s why annuals are so much easier to control than perennials.
Sprouts vs. established weeds
What is essential to understand is that corn gluten meal is a weed preventer included in the category of pre-emergent herbicides. It prevents the weed seedlings from forming roots and growing, but it has no herbicidal effect on established weeds.
How to use corn gluten meal as a herbicide
Corn gluten meal needs a “perfect storm” to work effectively on weeds. Three essential factors need to come together so CGM can act as a herbicide:
- Getting the CGM into the soil around the germination time of weed seeds
- Catching a dry spell
- Spreading the proper amount of CGM
Pro tip: The general timing and method of applying corn gluten meal is about the same as applying any weed and feed.
Weed germination time
For corn gluten meal to be effective as a weed killer, you must apply it before seed germination. That’s late March to mid-April for most summer weeds and late August for winter weeds. But these average germination periods are seldom precise enough for pre-emergent herbicides, so let’s dig a little deeper.
Germination time varies by location
The United States stretches across multiple climate zones, so the weed germination period differs from state to state.
Suppose you live in North Dakota, Minnesota, or Montana. In that case, you’ll most likely spread CGM mid-spring, from early April to early May, when daffodils and forsythias open their flowers.
On the other hand, in the far South, in Texas, Arizona, and Florida, the best time for pre-emergent herbicide use is in early spring, around March 15, when the dogwood blooms.
Soil temperature is an excellent indicator of germination time
Using the soil temperature to estimate the correct application time for CGM (and any other pre-emergent herbicide) is the key to accurate timing. You measure it with a soil thermometer at a depth of about 3 to 4 inches. Or use an online map like this to check your area’s soil temperature trend.
Here are the germination temperatures for the most common lawn and garden weeds.
|Type of Weed||Soil Temperature for Germination|
Rain forecast and dry spells
Corn gluten meal needs a dry period to be effective. It works by drying out the young roots of new sprouts. If it rains and the soil gets moist, weeds can grow new roots and recover from the weed-killer treatment. Plan the application when the weather forecast shows at least 48 hours without rainfall.
How much CGM to apply and steps to apply it
You must apply at least 20 pounds per 1,000 square feet using corn gluten meal with 60 to 65% protein to see results. Tests done by Turf Science researchers at Ohio State University show that 40 pounds per 1,000 sq. ft. is even better.
Once you find the right time to apply corn gluten meal and are set on a proper application rate, follow these steps:
1. Hand-pull all visible weeds from your lawn. They are too old to be damaged by CGM. Instead, the nitrogen in corn gluten meal helps them grow.
2. Dethatch the lawn and rake the soil surface to help corn gluten get near the weed seeds.
3. Use a garden spreader to apply the herbicide evenly over the lawn. Check if the spreader allows an application rate of 20 pounds/1,000 sq. ft. – for most models, this rate is over their maximum level. If that’s the case, make more runs to ensure the proper rate to control weeds effectively.
4. Lightly water the lawn. Corn gluten meal needs to be watered in to activate. Ensure about ¼ inch of water using a garden hose with nozzles or the sprinkler system. Do not overwater at this stage, or you can render the herbicide ineffective.
How effectively does corn gluten meal kill weeds?
After a correct first application, you can expect 40% to 60% effectiveness. Like most natural herbicides and pesticides, corn gluten meal works slowly and is a long-term treatment.
The second application can result in a 70% – 80% reduction in the weed population, and if used repeatedly for 2 or 3 years, it can eliminate over 90% of the weeds in your lawn and garden.
Note that these percentages are for the best-case scenarios where you apply CGM at the right time, spread it correctly, and there’s no unexpected rain to moisten the soil too soon after the application.
Results can also vary with soil type, temperature, and microbiome.
Where to buy corn gluten meal and how much it costs
Corn gluten meal is sold as a powder, in granular form, and pelletized. It’s also used as a main ingredient in various natural weed killers in both solid and liquid forms. Granular CGM is the most common and easy to use.
You can buy raw corn gluten meal from local farms and feed stores (be sure to check the protein content if it’s labeled as animal food – you’re looking for 60 – 65% protein) and from garden stores, where you’ll have a better chance of finding the herbicidal kind.
Corn gluten meal and CGM-based natural weed killers are available online in home & garden and retail stores. Here are some examples of popular products:
- Amazon – Jonathan Green 11591 Corn Gluten Lawn Fertilizer
- Home Depot – Purely Organic Weed and Feed Lawn Food
- Lowe’s – Preen Natural Vegetable Garden Weed Preventer
- Walmart – Old Cobblers Farm Corn Gluten All-Natural Weed Prevention
The average price of corn gluten meal (powder, granular, or pelletized) ranges from $1.40 to $4 per pound. It costs about $50 – $65 per gallon in liquid form. Compare these products to the best weed and feeds on the market, including synthetic chemicals and other organic options.
The granular price is in a similar range to chemical herbicides. The costly part comes from the higher amount of CGM you need for effective results. While CGM needs 20 to 40 pounds per 1,000 sq. ft. to be effective, synthetic fertilizers use a rate of 1 to 5 pounds.
The fertilizer side of CGM
Corn gluten meal is also a natural slow-release nitrogen fertilizer. It contains 9 to 10% nitrogen by weight and no phosphorus, making it excellent for classic and eco-friendly lawn care.
When you use it only as fertilizer, spreading 5 to 10 pounds per 1,000 sq. ft. covers the recommended nitrogen for one application on turfgrass, which is 0.5 to 1 pound.
If you use it as weed and feed, you’ll need to spread at least 20 pounds per 1,000 sq. ft. for good herbicidal results, meaning 2 pounds of nitrogen per 1,000 sq. ft.
The high nitrogen content can be a problem, but not always. Corn gluten meal releases nitrogen slowly over 3 to 4 months, and it’s unlikely to burn roots or cause nitrogen pollution.
Still, talk to your cooperative extension agent before using it if you live in an area with high rainfall during spring, soil poor in organic matter that is easily flushed, or bans on high-nitrogen fertilizers.
Pros and cons of using corn gluten meal
Here are, in a nutshell, the main advantages and disadvantages of using corn gluten meal as weed and feed.
|✓ Natural and safe for kids and pets|
✓ Improves soil water retention
✓ Protects the soil microbiome, supporting nutrient absorption and plant growth
✓ Natural source of slow-release nitrogen
✓ Has a cumulative effect – results get better and better
✓ Does not change soil pH
✓ Safe for established plants
|✗ If timing is off, it supports weed growth instead of preventing it|
✗ Rain can reduce weed killer efficiency drastically
✗ Requires a high amount of herbicide per 1,000 sq. ft.
✗ More expensive than other options
✗ Can lead to nitrogen excess in some cases
✗ Challenging to find OMRI-listed products with CGM for organic gardening
Natural weed control alternatives to CGM
Even if attractive as a natural weed and feed, corn gluten meal costs can make it prohibitive for some landowners. Here are a few excellent natural alternatives to keep weeds under control with a better cost/efficiency rate.
1. Mulching flower and vegetable gardens
A thick layer of mulch, about 3 to 6 inches, spread over the ground prevents sunlight and heat from reaching the soil and weeds from germinating and growing. You can use grass clippings, dry leaves, bark, hay, etc. as mulch in your veggie garden or flower beds.
2. A good, steady lawn care routine
Aerate and dethatch yearly, mow and water the turf grass correctly, fertilize like a pro, and overseed every year. Proper lawn care is how you keep the turf healthy and dense enough to keep weeds at bay without herbicides.
3. Choose other natural herbicides
You can prepare homemade weed killers with natural ingredients like salt, vinegar, and essential oils or buy natural products from local garden stores and online retail shops. Here are some examples of popular natural herbicides you can try:
- Amazon: ECO Garden PRO – Organic Vinegar Weed Killer
- Walmart: Green Gobbler Vinegar Weed & Grass Killer
- HomeDepot: Mighty Mint Weed & Grass Killer
- Lowes: Natria Grass & Weed Control With Root Kill Herbicide
4. Hand-pulling weeds
While they’re in a small number in your lawn and garden, hand-pulling is a great method for removing weeds. Ensure you get all the roots out to prevent regrowth and remove the weed before it starts flowering and making seeds.
FAQ about corn gluten meal as weed killer
Corn gluten meal acts on all seeds, no matter the origin, including grass seeds, vegetable seeds, or flower seeds. It’s to be used only on established lawns. If you plan to overseed cool-season grasses in the fall, don’t apply CGM in late summer. If you need to reseed warm-season grasses, wait 4 to 6 weeks after application before spreading the seed.
Corn gluten feed is another product of wet-milling corn. Corn gluten feed has half the amount of protein compared to corn gluten meal, and it’s used mainly as animal feed and less as a herbicide.
Corn gluten meal is made of corn through a process called wet-milling. It has 60 to 65% protein content and 10% nitrogen.
Get your lawn back to its beautiful, weed-free look!
Weeds can become a nasty problem if they get out of hand. Since natural herbicides are a little pickier than chemical ones, it’s worth having a professional by your side when weeds become bossy. Take advantage of your area’s experienced lawn care companies and call a weed control expert to help you get your lawn back to its beautiful, weed-free look!
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