How to use corn gluten meal for weed control

Question: I heard you talking on your radio program about using corn gluten meal to keep the weeds from coming up in my beds. Can you give me a little more information on how and when to use this product?

Answer: Though they will not rid your lawn or garden of existing weeds, organic pre-emergent herbicides based on corn gluten meal will prevent any new weed seedlings from growing by drying out the emerging plant’s initial root. When used correctly, they’re a great weed preventative, particularly for annual weeds. They’re also a source of nitrogen as well.

Organic pre-emergent herbicide products are made from corn gluten meal, a byproduct of the corn milling process. The granules are distributed over the surface of the soil or mulch, forming an invisible barrier to weed growth. Be aware, however, that corn gluten meal kills the initial root of all seedlings, so do not use it where you intend to grow any plants from seed.

The timing of weed seed germination is based on soil and air temperatures as well as the type of weed in question, so it’s important to apply corn gluten at the right time. The product only remains effective for five to six weeks after application, so if you put it on at the wrong time, you’ll miss your window of opportunity for preventing weeds.

The best time to apply corn gluten meal depends on what types of weeds you’re trying to control.

• If you’re trying to prevent summer annual weeds whose seeds germinate in the spring, such as crabgrass, purslane, prostrate spurge (Euphorbia supine/ E. prostrata), and pigweed, corn gluten meal is typically applied to lawns and gardens in the early spring, when the soil temperature reaches about 50 degrees F four inches beneath the surface (which is usually around the same time the forsythia are mid-bloom and the redbud trees start to flower).

• If you’re trying to prevent winter annual weeds whose seeds germinate in the late summer or fall, such as bittercress, deadnettle, henbit and chickweed or perennial weeds whose seeds germinate in fall, apply the corn gluten meal in the late summer, as soon as daytime temperatures start to wane (here in Pennsylvania, that’s typically around the first week of September).

• The best weed control is obtained when applying the corn gluten meal twice a year, once in the spring and again in the early autumn.

• The more diligent you are when using these products the better. Each year you use them, the results are greatly improved. A study at Iowa State found that a huge reduction in weeds occurs with two to three years of use. Five years of use often results in 100% control of new weed seed germination.

There are many different brand names for these products, including Concern Weed Prevention and Espoma Organic Weed Preventer. If you choose to include organic pre-emergent herbicides in your weed management arsenal, follow all label instructions for application rates and safety precautions. I do not recommend using pre-emergent herbicides made from synthetic chemicals, such as those found in weed n’ feeds and other granular or spray products.

I’m an organic gardener and do not consider these products either safe or necessary, especially when corn gluten meal works so beautifully.