Earthworms & Grass

Soil Nutrition

• Grass grows best in soil with high nutrient content. Grass also thrives when organisms decompose dead grass thatch and material. Earthworms work like natural recycling machines. They help break down rotting matter, releasing nutrients for grass roots. As they tunnel through the earth, they help aerate the soil and move nutrients and water around. Healthy lawns nearly always have some form of worm activity contributing to the quality of the grass--even if you can't see any evidence of worms.

Castings

• Worms eat soil and take their nutrients as it passes through the digestive system. When it reaches the end of the worm, the creature ejects the digested soil. Large worms near the soil surface can create mounds of castings on grass lawns. Castings look like small coiled heaps of brown mud -- not the most attractive sight on a stretch of well-maintained grass. When the castings dry, they're easiest to remove by scooping up with a small shovel.

Treatment

• For grass lawns with serious worm problems, chemical worm killers provide effective treatment. In particular, earthworms will not tolerate chlordane, according to Michigan State University. In some cases, the substance will prevent the return of earthworms for the following two years after application with regular doses. Another option includes products containing arsenate. When handling pesticide products such as these, follow the product instructions exactly and ensure that no pets or children access the treated area.

Considerations

• Applying pesticide when the grass is wet will likely destroy more earthworms than application when dry. However, this method could have a negative effect on your lawn if you remove too many worms from the soil. In many cases you may need permission to use pesticides for earthworm removal. On small lawns with minor worm problems, you can reduce the population temporarily by pouring warm soapy water on the grass. This treatment draws the worms to the surface where you can pick them off and discard.