Lumpy Lawn? Could Be Earthworms

Earthworms, particularly night crawlers, can be abundant in moist soils that contain moderate, or greater, amounts of organic matter. Worms take in and process soil and organic matter, then deposit the remnants (castings) during nocturnal surface visits. The castings dry into crumbles, leaving a rough, uneven soil surface (Figures 1 & 2). Earthworms are a large component of a mole’s diet, so their presence can result in increased tunneling by these small mammals.

Figure 1. Earthworm castings. (Photo by B. Wilson)

Figure 1. Earthworm castings. (Photo: B. Wilson)

Figure 2. Close-up of earthworm castings. (Photo by B. Wilson)

Figure 2. Close-up of earthworm castings. (Photo: B. Wilson)

Earthworm Activity and Its Beneftis

No pesticides are registered for earthworm control because of their generally beneficial contributions to soil health. These creatures break down accumulated thatch, pull organic matter into the soil, and dig tunnels that allow increased aeration and water penetration. They also mix large amounts of soil into the thatch layer. This helps to increase microbial activity and enhances growth of turfgrass.

Earthworm activity depends directly on soil moisture and temperature. They become active when soil thaws in spring and move deeper as the soil warms and dries.

Management Options

There are few options to reduce earthworm activity or to mitigate surface disturbance. A roller may be used to flatten castings. Some golf course managers top-dress with sand in areas where earthworms pose chronic problems. The thought is that this abrasive material will irritate the soft outer covering of earthworms and force them to relocate to sites where their activity is less objectionable.

By Lee Townsend, Extension Entomologist


Posted in Lawn & Turf