weed seed inhibitor

Water it in right after application.

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.

lawn and corn gluten meal.

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.

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.

Effective on All Weed Seed.

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.

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.

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

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.

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

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.

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.

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 .

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.

Dr. Nick Christians’ original field work showed that c orn 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.

Corn Gluten Meal – Does it Work?

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.

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.

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.

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.

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

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.

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.

What is Corn Gluten Meal?

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.

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

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.

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.

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.

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 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.

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

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.

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.

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

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.

How Much Is Needed?

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.

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.

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.

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.

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 Downside.

Application Timing.

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.

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.

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.

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.

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.

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 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.

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.

“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.

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.

“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.”

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.

“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.”

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.

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.

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

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.

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.