Corn gluten meal to be exact-is a by-product of the corn milling process used to make corn meal and corn syrup. It has been used for years as a supplemental nutrient in hog feed and is VERY effective on lawns and in gardens as a plant food and weed suppressant. This is a great non-toxic alternative to the typical chemical products out there on the market and thankfully this is becoming widely available in "big box stores."
As a plant food, corn gluten has a N-P-K (Nitrogen-Phosphours-Potassium) ratio of 9-1-0, or 10% nitrogen by weight. As a weed suppressant, corn gluten acts as a natural "pre-emergent" meaning it stops seed germination by drying out a seed as soon as it cracks open to sprout. This is GREAT for stopping new weeds seeds from germinating, it is also great for stopping new grass seed from germinating, so do NOT put this on your lawn if you are over-seeding with grass seed or you will NOT get a good-lookin lawn!
(Image from www.eartheasy.com)
To successfully kill weeds with corn gluten meal, timing is crucial. You want to apply this as seeds as sprouting. Spring application for Northern Virginia, DC and MD when "forsythia begins to bloom," or "two weeks before the first crocus, early daffodils, and blooming tulips" emerge.
If you are seeding your lawn and would still like to prevent weeds you want to use a product called Tupersan®. This will still allow grass seed to germinate but will kill any emerging weed seeds such as crabgrass. When seeding, the soil temperature needs to be in the 60 degree range for the seed to germinate, so some weeds may be up, tupersan will kill anything in the "two leaf stage", so you can still get a jump on any early weeds by using this product.
(Image from www.pbigordon.com)