Controlling Crabgrass and Dandelions Organically
by Erin Hynes
If you want a green lawn with few weeds, but you don’t like the idea of using synthetic fertilizers and weed killers, the answer just might be an ingredient used in pet food: corn gluten meal, a byproduct of corn milling used in food for cattle, poultry, fish, cats and dogs.
Corn gluten meal is proving to be the magic lawn-care bullet — it kills the seeds of crabgrass, dandelions and many other weeds, while the nitrogen in it feeds the lawn. Pretty impressive for a material your pet can safely eat.
A Corny Discovery
The weed-killing, grass-feeding powers of corn gluten meal were discovered accidentally at Iowa State University, where researchers were studying the effect of a specific fungus on common bentgrass, a turf used on golf courses. To get enough of a fungus for the study, they grew it on food-grade corn meal — the same stuff in corn meal muffins.
When they transferred the fungus to outdoors test plots, they noticed that the bentgrass grew poorly, and they traced the cause to the corn meal. Eventually, they figured out that the weed-killing compound in the corn meal was the corn gluten.
Where to Find It
Corn gluten meal packaged for use on lawns is available at garden centers and online. Stores that sell feed for livestock stores usually carry feed-grade corn gluten meal. Iowa State University’s position is that feed-grade corn gluten meal does not work as well. However, many gardeners claim to get good results with the feed-grade material.
Timing Is Everything
Whichever type you choose, timing is critical. Corn gluten meal kills weeds just as they begin to sprout, not ones that have established roots, so you have to apply it just as the weed seeds spring to life. You can’t go by the calendar date — you have to look for Nature’s cues. In spring, it’s when forsythia and crocuses bloom. In late summer, it’s when the nights start to cool off.
Besides keeping watch for forsythias flowering, you can also scrutinize the ground for the first tiny seedlings of dandelions and crabgrass. If crawling on your knees with a magnifying glass isn’t your style, you can also call a garden center or the county office of the Cooperative Extension Service.
It’s also critical to apply when no rain is predicted for five days. For one thing, you don’t want the corn gluten meal to wash away. Also, that dry period is crucial for killing weeds that have germinated but not formed a root; if it’s too wet, they can recover (as is true of any preemergence weed killer).
On the topic of timing, corn gluten meal also inhibits the seeds of lawn grass, so if you’re planning to overseed a thin lawn or bare spots, wait a few months (how long the seed-killing effect lasts depends on several things, such as rainfall and how many microorganisms live in the soil). A good approach is to apply the corn gluten meal only in spring and then seed the lawn in fall.
How to Apply
When no rain is predicted for several days, use a fertilizer spreader to apply corn gluten meal at a rate of 20 pounds per 1000 square feet. Sweep up any that falls on paved areas; it doesn’t present a hazard if it washes into the sewer, but it’s bright orange color is going to make the neighbors wonder what you’re up to this time.
Water the area lightly to moisten but not dissolve the corn gluten meal, and then let it dry.
After a few days, you might find yourself thinking “What is that SMELL?” and checking the refrigerator for forgotten potato salad. It’s true, for a few days corn gluten meal sometimes smells like rotting food. But it’s not as bad as the chemical smell of weed killers. And you might have potato salad hiding the back of the fridge.
Corn gluten meal doesn’t kill existing weeds, so you still have to pull out dandelions and other perennial weeds (ones that come back from roots every year). But it does control their seeds, so between the corn gluten meal and the pulling, you can get them under control over time. Annual weeds such as crabgrass don’t grow back from their roots, so you can either pull those or leave them to freeze over the winter.
If you consistently use corn gluten meal in the spring and fall, at the right time, you’ll notice that the lawn is healthier and less weedy season after season.
Garden author Erin Hynes has written several books about organic gardening. She holds a masters degree in Weed Science from Penn State.