If you have called the Extension office about organic fertilizers, you were probably told to use corn gluten meal (CGM). The next question is invariable “what the heck is that and where do I get it?” This article should answer all your questions.
In about 1980 some bright farmer noticed that where he had spilled CGM, the grass was greener and had fewer weeds than nearby grass. This led to Iowa State University to conduct a study that continued into the 2000s. This is information from that study.
CGM will control crabgrass seedlings when used as a preemergence herbicide. It also acts against germinating broad-leaf weeds’ seedlings including dandelions. The nitrogen content is about 10% in an organic form and is considered to be a slow-release source. It is slower than urea, but the grass treated with it was greener over the growing season. If we have a dry summer and you don’t water, the grass obviously will not stay nice and green.
The bags will be just plain brown as this is actually cattle feed. The university suggested rate of application is 20 pounds per 1,000 square feet. You should see the fertilizer on the grass as it looks like powdered cheese. The first applications should be in late May or early June. The easiest way to remember this is to apply it when the daffodils just start showing color. That means the soil is an ideal temperature for crabgrass and some broa-dleaf weeds start to appear. The second application is recommended for late October. This will give your grass a “minimally acceptable” (university words) lawn color throughout the growing season. Putting down fertilizer this time of year is recommended because the nitrogen feeds the grass as it is pulling food down into its roots in the fall. This leads to a thicker lawn next spring.
One warning, this stuff will not kill your dandelions. It may reduce them a bit to start but then they all come back. This is not a bad thing as dandelions are the first pollen-laden blooms in the spring. The early pollinators depend on them for food after their long journey north. Another so-called weed, white clover, is actually good for your lawn. It is a nitrogen fixing plant. Besides, the bees love it, and we love clover honey.
Conclusion. A minimum of two CGM applications are needed to provide minimally acceptable lawn color throughout the growing season. It won’t control dandelions but will kill emerging crabgrass. You should set your lawn mower to cut the grass at 3 inches for better control of dandelions and other weed seeds that may not have been killed by the early application of CGM . Taller grass shades out many weeds. Grass grows slower from 2 inches to 3 than from 1 inch to 2. Conclusion, cutting grass tall saves you lawn-mower time.
Users have noted that it takes about three years for the full effect of this fertilizer to improve your lawn. Because it is organic, it improves the soil unlike artificial fertilizers.
Some stores, like the men’s toy store, now carry CGM, but you should be able to get it at any feed mill.
Bev Johnson is a Master Gardener with the University of Minnesota Extension. Her column appears in the Weekend Edition.