Updated: Feb 14, 2022
ORGANIC WEED PREVENTION
Any weed expert will tell you that the best way to keep weeds out of your lawn and flowerbeds is to never let them get started. Keeping your turf thick and healthy, and mulching flowerbeds does a lot to help prevent weeds. The other key is regular applications of a pre-emergent herbicide. For organic gardeners, that product is Corn Gluten Meal.
A happy accident back in 1986 led researchers at Iowa State University to discover that Corn Gluten Meal prevents seed germination. Since then, lots of research has been done on whether Corn Gluten Meal is, in fact, an effective weed control, and the answer is a resounding “YES!”
There are some tricks, though. Here’s an overview of what it is and how it works, along with the secrets to getting the most out of it.
Make Sure You Get The Real Thing
Corn Gluten Meal is a by-product of the corn milling process. Long before it became famous as a weed suppressant, it was used as a supplement in hog feed. Corn Gluten Meal is 100% organic, and entirely edible, which means it is completely safe to use around pets and children.
Unprocessed Corn Gluten Meal has a very fine, powdery texture. It can be broadcast by hand or by a fertilizer spreader. It will look like a layer of pollen on the soil. Apply to lawns, or directly on bare earth, or around new plantings.
Corn Gluten Meal is more effective for weed suppression than granulated (spreadable) Corn Gluten. But both make excellent all-nitrogen fertilizers.
In recent years, some suppliers have been substituting dry-milled corn gluten feed and distillers grain for real Corn Gluten Meal. These are often sold at other garden stores as a gardening product. They are not Corn Gluten Meal and they will not work. Real Corn Gluten Meal has a higher level of protein (60%), which is critical to seed suppression.
Marshall Grain ensures that the Corn Gluten Meal we sell is registered with the State of Texas as real Corn Gluten Meal for horticultural use.
Marshall Grain also offers spreadable, or granulated, corn gluten.
Either product can be distributed using any type of fertilizer spreader. The powdery meal is a bit messy to apply, especially on windy days. The granules are easier to spread and much less messy, but they don’t cover the ground as well, which reduces the product’s effectiveness for weed control. For maximum effectiveness, the meal is the best choice for your lawn. On the other hand, the granules can be mixed with water into a paste to use as a patch for localized weed suppression. The patch will keep weeds from sprouting up between plants.
Both types of Corn Gluten contain 9% nitrogen by weight (i.e., 100 lbs of corn gluten contains 9 lbs of nitrogen) to help make your lawn greener, so it’s a great organic fertilizer, plus it adds organic material for increasing microbial activity. Thanks to this dual function, many people refer to it as an organic “weed and feed” product.
No Other Organic Pre-Emergent
For now at least, Corn Gluten Meal is the only organic pre-emergent available. American Lawns explains how it works as an herbicide. Turns out that it has some naturally occuring chemicals called peptides that actually inhibit root formation of a seed at the time of germination.
One application of Corn Gluten Meal keeps working to suppress seed germination for 4 to 6 weeks. (Heavy soils, extended rainy weather, and hot spells may require additional applications. It works on all types of seeds — and only on seeds. It does not harm existing plants. When used correctly, over time you will have fewer broad leaf and grassy weeds, including Crabgrass, Dandelions, Clover, Henbit, and many others. But because it is non-selective, you should avoid applying it in areas where desirable plants might be germinating. If you plan to overseed your lawn, start flowers, or grow vegetables from seed, be sure to wait at least 6 weeks after applying it.
Timing Is Crucial
Get the timing right: Most weeds germinate when over-night temperatures are in the mid-50s.
Timing is critical, says About.com, for both organic and synthetic chemical pre-emergents. Weeds don’t have calendars. They sprout as soon as the weather is right. Sunny days and temperatures in the mid-50’s begin the cycle of germinating and re-seeding. This is the signal that it’s time to put out your pre-emergent.
In North Texas, weed sprouting season usually starts around mid-February and continues throughout the growing season. The process slows down considerably during the heat of summer, but then picks up again when temperatures cool in the fall.
The seedling stage of a weed can last 8 to 15 weeks, depending on temperature and growing conditions. Since they are usually well-hidden within your lawn, this means that the weeds you see in the springtime actually germinated in the fall. Likewise, seeds that germinate in the spring don’t become visible until fall. All this boils down to the need to treat at least twice per year – once in the spring and once in the fall.
The easiest way to tell when it’s time to apply it, is to watch for dandelions. As soon as you see your first dandelion, put it out. Don’t wait! Apply it at a rate of 20 lbs per 1000 square feet to make sure you get sufficient coverage.
If applied consistently, at the rate of 20 – 40 lbs per 1000 square feet of lawn, Iowa State University research shows, the results of using Corn Gluten Meal are cumulative: The longer you use it, the better your lawn will look!
Too Much of a Good Thing
One problem with Corn Gluten Meal can be too much water. Some is helpful, but too much can spoil the job.
Corn Gluten Meal needs to be watered in within 5 days of application. If no rain occurs within that window, you should water it in with 1/4 inch of water. But heavy rain or excessive irrigation will wash it away before it can dissolve into the soil. This means that the watering-in process must also be followed by a dry period of a day or two to prevent the seedling from growing another root. If heavy rain is predicted, it may be best to wait for drier weather before putting it down.
You may prefer to water your lawn before you apply Corn Gluten Meal — especially if you plan to use a broadcast spreader. Being a fine powder, Corn Gluten Meal easily blows around, getting on you and everything else in your yard. Broadcast spreaders cause the powder to fly out to the sides, rather than just dropping straight to the ground, which encourages more mess. Windy days are also problematic. Watering lightly first will help keep the dust to a minimum and make it stick to the lawn immediately.
Corn Gluten Meal Facts
The only 100% organic pre-emergent herbicide available
Safe for people and pets
Inhibits root formation at the time of seed germination
Only “real” Corn Gluten Meal (“wet milled”) will work for seed suppression
Works on all types of seeds
Timing is critical. Application must be synchronized with weed germination
Must be watered in by rainfall or irrigation within 5 days of application to activate
Too much rainfall or hot spells can reduce effectiveness
Must be applied 2x yearly in spring and fall
Effects last for 4 to 6 weeks
Provides a slow-release 9% nitrogen source
Apply 20 – 40 lbs per 1000 square feet of lawn
A dry period of a day or two must follow the watering in to prevent the seedling from growing another root.
Effectiveness improves over time
Corn Gluten Meal only works on seeds. It will not harm existing plants.
Adds nitrogen and organic matter to the soil, which increases microbial activity
If you’ve followed these guidelines and used Corn Gluten Meal consistently you can expect weed suppression equal to or better than a chemical pre-emergement. And you will rest easier knowing that your garden is a safer place for you and your family to enjoy.
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