The activity of earthworms, especially night crawlers, often creates a rough lawn surface that can be both annoying and dangerous. The small castings left on the soil surface by earthworms are only one of many factors that contribute to lawn bumpiness, though they are often the most recognizable. Another "problem" associated with earthworms is the movement of large numbers to places where they are unwanted (for example, on sidewalks or patios, and in swimming pools).
To hear the passion with which people seek a "control" for earthworms makes the worms sound like the worst pest imaginable. Of course, earthworms are valuable to the overall health and tilth of the lawn. Their activity improves the growing environment by increasing air and water movement in the soil and they help decompose thatch and 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 controls. Compared to the pesticides (especially insecticides) used one or two decades ago, 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 species and variety suited to the site, and through proper fertilization, mowing and irrigation.
Mechanical means to reduce bumpiness will be necessary to eliminate existing roughness. Core aerifying, power raking and verticutting are all mechanical processes that will break down some of the bumps in the lawn. Roughness accumulates over several years and it 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 in not advised.
This article originally appeared in the April 14, 1995 issue, p. 47.