Prevent weed seeds from sprouting with corn gluten meal

Corn gluten meal did not prevent weeds from germinating in OSU study

CORVALLIS, Ore. – Corn gluten meal is a natural substitute for a synthetic “pre-emergence” herbicide and has been advertised as a more environmentally friendly way to control weeds.

A pre-emergent herbicide is one that kills seedlings as they germinate. Pre-emergent herbicides generally have to be applied and watered in before weed seeds germinate. Other herbicides, such as glyphosate (e.g. Round Up) kill plants after they have emerged.

A by-product of commercial corn milling, corn gluten meal contains protein from the corn. It poses no health risk to people or animals when used as an herbicide. With 60 percent protein it is used as feed for livestock, fish and dogs. It contains 10 percent nitrogen, by weight, so it acts as a fertilizer as well.

The use of corn gluten meal as an herbicide was discovered by accident during turfgrass disease research at Iowa State University. Researchers noticed that it prevented grass seeds from sprouting. Further research at Iowa State showed that it also effectively prevents other seeds from sprouting, including seeds from many weeds such as crabgrass, chickweed, and even dandelions. Components in corn gluten meal called dipeptides are apparently responsible for herbicidal activity.

Researchers at Oregon State University were not able to duplicate research results reported by Iowa State researchers, said OSU turf grass specialist Tom Cook. A former graduate student, Chris Hilgert completed his masters thesis by investigating corn gluten meal use as a pre-emergent herbicide in shrub beds and on lawns.

In their trials with corn gluten meal, Hilgert and Cook found the following:

Corn gluten meal did not control any weeds in any trials under any circumstances over a two-year period. They found no evidence of pre- or post-emergence weed control in any of their trials. Because it contains 10 percent nitrogen, corn gluten meal proved to be a very effective fertilizer, causing lush, dense growth of turfgrass and of weeds in shrub beds.

James Altland, nursery crops specialist at OSU’s North Willamette Research and Extension Center in Aurora, spoke to his observations when corn gluten was used in plant nurseries as a pre-emergent herbicide.

“I’ve seen nursery situations where the applied product caused a bad odor, as do some herbicides, and attracted rodents,” said Altland. “In nursery situations where the goal is complete weed suppression, my overall impression is that it doesn’t work that well.”

“My overall impression has been that in turfgrass it provides a lot of nitrogen,” added Altland. “Thicker, denser turf from high nitrogen rates will reduce weed numbers alone, without the help of herbicides.

“Applying 20 pounds per 1,000 square feet of corn gluten meal would be equivalent to two pounds of nitrogen per 1,000 square feet. That’s a lot of nitrogen! Applying that much nitrogen is not good for the environment. It doesn’t matter if it’s a ‘natural’ fertilizer or not. That nitrogen will ultimately be converted to nitrates, which potentially could leach into groundwater.”

It is not clear why the commercial version of corn gluten meal used in OSU trials was not effective, said Cook. One possibility is that the product as formulated for sale has a short shelf life and loses potency during manufacture, shipping and storage. Further research needs to be done to test this hypothesis, he said.

If you want to discourage weeds from germinating and growing in your garden beds over the winter, try adding mulch to soil surfaces. Use a minimum of three to six inches of composted material. Tuck mulch up to the shoulders of your perennials, but don’t cover the growing crown until freezing cold weather sets in. If you cover plant crowns too soon, they may begin to grow under the mulch and could be killed when temperatures dip.

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Shredded bark, leaves, mint hay, wood chips, or yard waste all offer benefits. Large chunky material such as fresh clean wood chips and bark nuggets work best for weed control, as they are low in available nutrients so won’t fertilize germinating weeds.

Avoid mulching with hay or with ryegrass straw. Their seeds will sprout to create an unnecessary headache for you in the spring. And don’t use grass clippings from a lawn treated with a weed-and-feed preparation. The herbicide in the clippings can damage your shrubs.

A low-nutrient mulch such as well-rotted sawdust will benefit shrubs such as roses, azaleas, rhododendrons and hydrangeas. Lilies, dahlias and spring bulbs will do better with this type of mulching also. But be aware that composted sawdust or other fine organic material may contribute to weed growth.

Caneberries benefit from higher-nutrient mulches such as composted manure. Dormant vegetable beds can use a six-inch blanket of manure and leaves. Rhubarb and asparagus beds do best covered with a mix of well-composted straw and manure.

Over the winter, the composted material will mix with the soil, so a second application of mulch in March or April will keep your garden soil in better condition.

Corn Gluten: An Organic Pre-Emergent Herbicide

Kelly Burke is a professional turf manager for a manicured corporate campus in New England. He is accredited in organic land care and is a licensed pesticide applicator. He formerly managed the turfgrass as a golf course superintendent and has held several senior management positions at private country clubs overseeing high maintenance lawns.

Kathleen Miller is a highly-regarded Master Gardener and Horticulturist who shares her knowledge of sustainable living, organic gardening, farming, and landscape design. She founded Gaia’s Farm and Gardens, a working sustainable permaculture farm, and writes for Gaia Grows, a local newspaper column. She has over 30 years of experience in gardening and sustainable farming.

Emily Estep is a plant biologist and fact-checker focused on environmental sciences. She received a Bachelor of Arts in Journalism and a Master of Science in Plant Biology from Ohio University. Emily has been a proofreader and editor at a variety of online media outlets over the past decade.

Corn gluten meal is a powdery byproduct of the corn milling process. Originally used as a supplement in hog feed, corn gluten has become a common organic alternative to synthetic chemical herbicides. It can be effective as a pre-emergent herbicide used to control crabgrass and other lawn weeds, and it also has nutritional properties. Corn gluten meal is about 10 percent nitrogen by weight, meaning 100 pounds of corn gluten contains 10 pounds of nitrogen. This organic source of nitrogen is slowly released over a three- to four-month period.

How Corn Gluten Works

Corn gluten does not prevent weed seeds from germinating, but it does inhibit those seeds from forming roots after germination. This means that applications must be very carefully timed. When the application of corn gluten is timed correctly, crabgrass seeds germinating will form shoots but not roots, and will therefore die, provided there is a short dry period after seed germination. However, if conditions are too wet immediately after seed germination, the weed can recover and establish a root.

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Application Timing

Corn gluten is useful only as a pre-emergent herbicide; it provides no post-emergent weed control. If crabgrass and other weed seeds have already germinated and taken root, a late application of corn gluten will only serve as fertilizer for the weeds. Further, applications of corn gluten need to be precisely timed around rainfall or watering. After application, corn gluten needs to be watered in, either by rainfall or by artificial watering, within five days of application. Rainfall of about 1/4 inch, or a comparable artificial watering, is ideal. After this, a dry period of one or two days is required to prevent weed seedlings that have germinated from growing roots.

In other words, corn gluten needs water just after application, but a dry period is then required in order for germinated weed seeds to have their root production inhibited. It can be quite difficult to get this application timing precisely correct.

The first application of corn gluten won’t suppress all of the weed seeds, and a single application may help suppress weeds for four to six weeks. Heavy soils, extended rainy weather, and hot spells may require a monthly application or a second application in late summer. The initial results may be disappointing but after several applications, corn gluten sometimes reaches 80 percent effectiveness at controlling crabgrass.

How Much Is Needed?

Application rates vary by form: powder, pelletized or granulated. The standard application rate is 20 pounds of corn gluten per 1,000 square feet of lawn. This rate also provides about 2 pounds of nitrogen per 1,000 square feet.

The effects of corn gluten are cumulative, meaning that the results improve with repeated use over time.

The Downside

Some experts are critical of using corn gluten as a pre-emergent crab-grass killer, pointing to several points:

  • Corn gluten is costlier than conventional pre-emergent herbicides. Because multiple applications are often required, you could be handling hundreds or even thousands of pounds of the product, depending on the size of the yard. Sprayable, liquid forms of corn gluten can make applications easier, but they are still costly.
  • Timing is critical for both organic and synthetic chemical pre-emergents. It’s very important to remember that all pre-emergents, including corn gluten, will suppress all seeds, including grass and flower seeds. If you are using non-selective pre-emergents in the spring and summer, any lawn seeding should be done in the fall.

Definition

A synthetic chemical pre-emergent is a non-organic herbicide that is applied to the landscape prior to weeds and other unwanted plants growing. In essence, it prevents those plants from emerging from the soil where seeds might lie.

  • The nitrogen in corn gluten has drawbacks. Some turf specialists argue that extra nitrogen only gives weeds the advantage.
  • Encouraging new grass is more effective. Crabgrass is a filler weed that thrives in bare spots or areas with thin turf grass, and organic turf specialists contend that seeding with new grass is just as effective as applying pre-emergent herbicides such as corn gluten. Dense, healthy turf will naturally crowd out crabgrass, so growing more grass and filling in those thin areas and bare patches may be a better solution.
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Bottom Line

Corn gluten does work as a pre-emergent herbicide, through a mechanism that inhibits germinated weed seeds from establishing roots. But timing the applications correctly is tricky, and it may require repeated applications in order to really see the desired results. Further, corn gluten can also inhibit new turf grass seeds from becoming established.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Cornmeal As Weed Killer And Pest Control: How To Use Cornmeal Gluten In The Garden

Cornmeal gluten, commonly referred to as corn gluten meal (CGM), is the by-product of corn wet milling. It is used to feed cattle, fish, dogs, and poultry. Gluten meal is known as a natural substitute for chemical pre-emergent herbicides. Using this cornmeal as weed killer is a great way to eradicate weeds without the threat of toxic chemicals. If you have pets or small children, gluten meal is a great option.

Gluten Cornmeal as Weed Killer

Researchers at Iowa State University discovered by accident that cornmeal gluten acts as an herbicide while they were doing disease research. They saw that corn gluten meal kept grass and other seeds, such as crabgrass, dandelions, and chickweed from sprouting.

It is important to note that cornmeal gluten is only effective against seeds, not plants that are mature, and is most effective with corn gluten having at least 60% proteins in it. For annual weeds that are growing, plain cornmeal products will not kill it. These weeds include:

Perennial weeds will not be damaged either. They pop back up year after year because their roots survive under the soil over winter. Some of these include:

However, cornmeal gluten will stop the seeds that these weeds shed in the summer so that the weeds will not increase. With consistent use of gluten meal products, these weeds will gradually decline.

How to Use Cornmeal Gluten in the Garden

Many people use corn gluten on their lawns, but it can be safely and effectively used in gardens as well. Using gluten cornmeal in gardens is a great way to keep weed seeds from sprouting and will not damage existing plants, shrubs, or trees.

Be sure to follow the application instructions on the package and apply before weeds start to grow. Sometimes this can be a very tight window, but is best done in early spring. In flower and vegetable beds where seeds are sown, be sure to wait to apply at least until the seeds are grown up a bit. If applied too early, it can prevent these seeds from sprouting.

Using Cornmeal Gluten to Kill Ants

Cornmeal gluten is also a popular method to control ants. Pouring it wherever you see ants traveling is the best option. They will pick up the gluten and take it to the nest where they will feed on it. Since the ants cannot digest this cornmeal product, they will starve to death. It may take up to a week or so before you see your ant population dwindling.

Tip: If you have large areas to cover, you can try a spray form for ease of application. Apply every four weeks, or after heavy rains, during the growing season to maintain effectiveness.