Corn gluten meal is an organic herbicide that also works to fertilize your lawn. It's a protein by-product of the corn milling process and is safe enough to use in food for animals such as dogs and cows. However, it's lethal to weed seeds and can add a healthy nitrogen boost to an established lawn. If you're trying to establish a new lawn, give yourself a couple of months between spreading the herbicide and your seeds.
How Long to Wait
Corn gluten meal isn't particular about separating grass seeds from weed seeds; it kills them both. Give the corn gluten time to lose its effectiveness from exposure, at least six weeks. Eight weeks is even better, especially if there hasn't been much rain. If you must plant sooner than six weeks, water the area thoroughly for several days to wash away as much of the herbicide as possible.
How It Works
Corn gluten meal works as a pre-emergent herbicide. If you spread it while seeds are in the ground but before they become seedlings, the amino acids in the corn gluten protein stop the seeds from germinating. Spreading it in the early spring and late summer can stop both hot weather and cold weather weeds from getting a foothold. If you know you want to plant grass seed, spread the corn gluten meal early enough so that you can still plant the seeds during the right timeframe. For example, for spring planting, spread the corn gluten meal in March so you can sow your grass seeds in May. This should give your grass plenty of time to become established before the hot summer weather appears.
What It Kills
Corn gluten won't kill all weeds in your lawn, but it's effective against such weeds as crabgrass, dandelions, quack grass and curly dock. Because it works well with most grassy weeds, there's a downside: it also is effective at keeping your grass seed from germinating. Spreading the seed too soon after using corn gluten can leave you without a lawn. Corn gluten is not quite as effective against perennial weed pests, such as red clover.
If you must use a pre-emergent herbicide at the same time you're spreading grass seed, look for one that is safe for grass seed, such as siduron. This is especially effective against crabgrass and is included in many standard crabgrass preventers. It also works well on weeds like foxtail and barnyard grass, while allowing your grass seed to germinate normally.
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