From gardeningknowhow.com, an interesting list of home-made weed klllers.
By Susan Patterson, Master Gardener
Cornmeal gluten is the by-product of corn wet milling. It is used to feed cattle, fish, dogs, and poultry. Cornmeal is known as a natural substitute for chemical pre-emergent herbicides. Using cornmeal as weed killer is a great way to eradicate weeds without the threat of toxic chemicals. If you have pets or small children, gluten meal is a great option.
Cornmeal as Weed Killer
Researchers at Iowa State University discovered by accident that cornmeal acts as an herbicide while they were doing disease research. They saw that cornmeal kept grass and other seeds, such as crabgrass, dandelions and chickweed, from sprouting.
It is important to note that cornmeal is only effective against seeds, not plants that are mature. For annual weeds that are growing, cornmeal products will not kill it. These weeds include foxtail, purslane, pigweed and crabgrass. Perennial weeds, including dandelions, quack grass and plantain, will not be damaged either. They pop back up year after year because their roots survive under the soil over winter.
However, cornmeal will stop the seeds that these weeds shed in the summer so that the weeds will not increase. With consistent use of cornmeal products, these weeds will gradually decline.
How to Use Cornmeal in the Garden
Many people use corn gluten on their lawns, but it can be safely and effectively used in gardens as well. Using cornmeal in gardens is a great way to keep weed seeds from sprouting and will not damage existing plants, shrubs or trees.
Be sure to follow the application instructions on the package and apply before weeds start to grow. Sometimes this can be a very tight window but is best done in early spring. Be sure to wait to apply in flower and vegetable beds where seeds are sown at least until the seeds are grown up a bit. If applied too early, it can prevent these seeds from sprouting.
Using Cornmeal to Kill Ants
Cornmeal is also a popular method to control ants. Pouring cornmeal where you see ants travelling is the best option. They will pick up the cornmeal and take it to the nest where they will feed on it. Because the ants cannot digest the cornmeal, they will starve to death. It may take up to a week or so before you see your ant population dwindling.
Tip: If you have large areas to cover, you can try a spray form for ease of application. Apply every four weeks, or after heavy rains, during the growing season to maintain effectiveness.