June 19, 2002
Woodbury Bulletin
Betsy Halden

Earthworms in lawns

We’ve all seen big fat earthworms on our walks, lawns, patios, or even swimming pools after a rain. This is a “problem’ associated with the movement of earthworms to places where they are unwanted. The activity of earthworms, especially “night crawlers” often contributes to a rough and bumpy lawn surface that can be annoying to a homeowner. To hear the passion with which people seek a “control” for earthworms you could believe that worms are the worst pests on earth, or more appropriately, in earth. Earthworms, however, are beneficial and valuable to the overall health of our lawns and gardens. Their activity improves the growing environment by increasing air and water movement in the soil and they help decompose thatch. They also help alleviate compaction.

There are no pesticides labeled for the control of earthworms. Although some pesticides and fertilizers are known to have an impact on earthworms, none can be recommended as a control. Today’s pesticides have relatively little impact on earthworm populations, in part because of the registration process that examines adverse environmental effects such as mortality to beneficial, nontarget organisms, including earthworms.

Various lawn care practices can help reduce the problem of a bumpy lawn. bumpiness in sparse, thin lawns will be less noticeable if a healthy thick turf is reestablished through reseeding with a turfgrass species/variety suited to the location. Proper fertilization, mowing, and irrigation will also help establish a healthy turf.

It will probably be necessary to use mechanical means to reduce roughness in the lawn. Core aerifying, power raking and verticutting are mechanical processes that will break down some of the bumps in the lawn. Roughness accumulates over several years and should be gradually removed instead of all at once.

Use of a heavy roller is not recommended. while rolling may remove some roughness, it also damages the turf by compacting the soil. Compacted soil reduces turfgrass vigor and eventually leads to a thinner lawn.

Although rough bumpy lawns and earthworms on the driveway are annoying, destruction of earthworms is not advised. Earthworms are beneficial and highly desirable participants in our gardens.

The University of Minnesota Extension Service Yard and Garden Clinic has a new website that can help you diagnose vegetable and bedding plant diseases. Log on to www.extension.umn.edu/projects/yardandgarden/diagnostics/ and follow the prompts.

Betsy Halden is a resident of Woodbury. She consulted Cornell Cooperative Extension and the University of Minnesota Extension Service materials when preparing this column. You can reach Betsy Halden at eahalden@comcast.net