Over the past decade, kaolin clay was introduced as a disease and insect control for various crops. Now, new research from the USDA suggests that this clay can be used to prevent weed growth as well.
In trials at the Agricultural Research Service lab in Kearneysville, West Virginia, researchers grew blackberries on soils treated with kaolin clay and those without the treatment. In one plot they mixed clay with soil at rates of 3 percent and 10 percent by volume. This created a kaolin clay "mulch" 1 to 2 inches thick. In another plot they sprayed a mixture of liquid kaolin clay directly on the soil to form a mulch layer. In both cases they found the clay treated plots had only a 3 percent weed cover - similar to an herbicide treatment.
However, blackberries that were planted prior to the kaolin clay treatments suffered phytotoxic damage after the clay was applied. No damage occurred in plots where the blackberries were planted after the treatment had dried, suggesting the wet kaolin clay can damage plants.
Kaolin clay was found to be an effective weed control because the 1- to 2-inch thick clay layer on the soil surface contained very little water and was very crusty, making it tough for weed seeds to germinate and grow.
Kaolin clay is available from garden centers and via mail order for pest and disease control, but more research is needed to determine how best to use it as a weed control. Stay tuned. For more information on this kaolin clay research go to the Agricultural Research Service's Web site.