Corn gluten meal is a powdery byproduct of the corn milling process. Originally used as a supplement in hog feed, its weed-suppressing properties are usually compared to that of chemical pre-emergent herbicides. Corn gluten is usually purchased as an organic alternative to chemically derived herbicides.
Corn gluten meal is also 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 Does Corn Gluten Work?
Corn gluten inhibits seeds from forming roots during germination. The application must be carefully timed before germination of crabgrass seeds, for instance. The seed will germinate and form a shoot, but not a root. Prior to germination, a short drying period is needed to kill the germinated, but rootless, plant. If conditions are too wet during germination, the plant will recover and form a root.
Corn gluten provides no post-emergent weed control. If seeds have already germinated, a late application of corn gluten will only serve as fertilizer for the weeds.
Applications of corn gluten should be timed with rainfall. If it doesn’t rain within five days of application, it needs to be watered in with 1/4 inch of water. A dry period of a day or two must follow the watering in to prevent the seedling from growing another root.
How Much Corn Gluten is Needed?
The first application of corn gluten will only suppress up to 60 percent of the weed seeds. One 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 repeated application in late summer.
The initial results may be disappointing but after several applications, it sometimes reaches 80 percent effectiveness.
Application rates vary by form: powder pelletized or granulated. The standard seems to be 20 pounds/1000 square feet.This rate also provides about 2 pounds of nitrogen per 1,000 square feet.
The effects of corn gluten are cumulative, meaning results improve with repeated use over time.
Downside of Using Corn Gluten
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 are still costly.
Timing is critical for both organic and synthetic chemical pre-emergents. It's very important to remember that all pre-emergents suppress seeds, including grass and flower seeds. When using non-selective pre-emergents, most of the seeding needs to be done in the fall.
Why Use This Pre-emergent at All?
While it may seem as though the nitrogen in corn gluten is a benefit, it is actually problematic. Some turf specialists, organic and conventional, do not recommend any early spring application of fertilizer.
They argue that the plant is growing enough on its own at this time, and fertilizingonly gives weeds the advantage.
Crabgrass is a filler weed. It will thrive in areas with thin turf or bare patches. Many organic turf growers contend that a bag of seed can be as effective at suppressing crabgrass as any pre-emergent herbicide.
Dense, healthy turf will naturally crowd out crabgrass, so growing more grass and filling in those thin areas and bare patches will result in minimized crabgrass pressure.