Earthworms & Lawns

Earthworms rise to the soil's surface after it rains because their underground tunnels flood.

Despite producing a bumpy appearance in the lawn, earthworms (Lumbricus terrestris) are beneficial. Earthworms pose no danger to the lawn. They do not consume the blades or roots of the grass but only subsist on decaying organic matter. They help the lawn to maintain its health and viability. An abundant earthworm population indicates a healthy lawn and rich soil.

Benefits

The burrowing behavior of earthworms benefits the soil by providing aeration. The tunnels help transport water to the lawn's root system and provide much needed oxygen directly to the lawn's roots. Earthworms dramatically reduce thatch buildup by consuming the dead grass. Their fecal matter, known as castings, helps to add valuable nutrients to the soil. During the day earthworms dwell beneath the soil in their tunnels but at night they rise to the surface to feed.

Drawbacks

An abundant earthworm population in the lawn makes excessive castings which gives the grass a bumpy appearance. The bumps can interfere with mowing. The brown mounds make the lawn's surface uneven which can make walking difficult for the elderly or handicapped to traverse across. Earthworms also draw moles into the yard who enjoy feeding on the worms. The moles make tunnels and holes in the lawn.

Lawn Care

Regularly raking the lawn will help reduce the bumps in the lawn and spread the nutrient rich castings throughout the lawn's surface. Consider using a power rake to gently break up the earthworm mounds without damaging the grass. A power rake is easier to use than a hand rake for a large yard. Allowing the topsoil to dry out between waterings often forces the earthworms deeper into the soil, which helps reduce casting bumps. Avoid mowing the lawn closely so the mounds are not noticeable. Tall grass can effectively hide the casting mounds.

Considerations

Avoid using a heavy lawn roller to try to compact the earthworm mounds because this will reduce the vigor of the lawn by compacting the soil. Grass roots do not grow well in compacted soil. Avoid applying harmful pesticides to the soil which may kill or damage the earthworms. Pesticides that contain carbaryl are especially harmful, according to the Houston County Extension Service at the University of Georgia.

References

• University of California: Earthworm --- Lumbricus Terrestris
• North Carolina State University Cooperative Extension; Earthworms as Pests in Home Lawns; S. Bambara; Jan 2003
• Utah State University; Over Hill, Over Dale: Earthworms in the Lawn; Kelly Kopp, et al; Jan 2005
• Iowa State University: Earthworms in Lawns; Donald Lewis; May 1999
• Colorado State University: Earthworms and Nightcrawlers in the Home Lawn; Tony Koski; Dec 2010
• Houston County Extension Service at the University of Georgia: Earthworms in Lawns

Resources

• Iowa State University: Earthworms in the Lawn; Donald Lewis; March 2005
• University of Nebraska Lincoln; Earthworms (Nightcrawlers) in Lawns; Don Janssen; April 2004
• Eartheasy; The Earthworm Lawn and Garden; June/July 200