Earthworms play a major role in the health of soil ecosystems. These invertebrates are responsible for significant soil aeration, improved water infiltration, and the recycling of nutrients through the decomposition of organic matter. However, the beneficial work they perform underground often leads to a visible nuisance on the surface, particularly for those maintaining a highly manicured lawn. The goal is to encourage these natural soil engineers to remain deeper within the soil profile, rather than pursuing their complete elimination.
Why Earthworm Surface Activity Causes Concern
Homeowners and turf managers seek control primarily because of the visible excrement deposited on the surface known as worm casts. These small, muddy piles of processed soil are the waste material left by certain species, such as the common nightcrawler (Lumbricus terrestris). The presence of casts is most pronounced during moist conditions in spring and autumn when earthworms are most active near the surface.
When these casts dry, they create a rough, uneven, and bumpy surface that detracts from the appearance of turfgrass. Mowing over the dried, gritty mounds is problematic because the abrasive soil quickly dulls mower blades and causes the casts to smear across the turf. This smearing action can smother the underlying grass, creating bare patches where weed seeds can easily settle and germinate. The resulting unevenness can also make walking difficult and reduce the quality of the lawn surface.
Non-Toxic Methods for Reducing Earthworm Activity
Managing the environment to make the surface less appealing is the most sustainable approach to controlling earthworm casts. Earthworms require moisture and organic matter, so reducing both near the surface encourages them to burrow deeper or move to a more hospitable area.
Water management is a practical first step, as earthworms are most active when the topsoil is consistently moist. Adjusting irrigation schedules to water deeply but infrequently allows the top few inches of soil to dry out between applications, making the surface less conducive to worm activity. This practice also promotes deeper root growth in the turfgrass, improving the lawn’s overall health.
Reducing the food source is an effective cultural control, since earthworms primarily feed on organic material like decaying leaves and grass clippings. It is helpful to box off and remove grass clippings after mowing, rather than leaving them on the lawn as mulch. Additionally, minimizing the accumulation of thatch—the layer of dead and living organic matter just above the soil—removes a ready food source for the earthworm population.
Manipulating the soil’s acidity can also provide a gradual reduction in earthworm presence, as most species prefer neutral to slightly alkaline pH levels. Applying acidifying products, such as ammonium sulfate or ferrous sulfate fertilizers, can slowly lower the soil pH over time. Soil tests are necessary before using these products to ensure the pH is not lowered to a point that harms the turfgrass, but maintaining a surface pH below 6.0 can be enough to deter many earthworm species.
For immediate aesthetic improvement, physical management of the casts is necessary. When the casts are dry, gently sweep, brush, or roll the area to break them up and disperse the soil back into the turf. It is important to wait until the casts are completely dry; attempting this when they are wet will only smear the muddy material, which can result in a compact layer that restricts water infiltration and smothers the grass.
Using Chemical Solutions for Immediate Removal
Finding a product legally approved for earthworm removal is difficult, as environmental regulations strictly limit the use of chemicals intended to kill or suppress beneficial soil organisms. Currently, there are few, if any, chemical pesticides registered specifically for homeowner use to control earthworms in turfgrass.
Some products targeting other turf pests, such as certain insecticides or fungicides, may have the unintended side effect of reducing earthworm populations. For instance, certain chemicals applied for grub control have been shown to reduce earthworm numbers by a high percentage as a non-target effect. However, using these products solely for earthworm control is inappropriate, costly, and not in accordance with label instructions.
A non-lethal, short-term chemical intervention involves using irritants to force the worms to the surface for manual collection and relocation. Solutions of dilute mustard powder or a mild soap mixture, known as a vermifuge, can be poured onto the turf to temporarily irritate the worms. This causes them to quickly emerge from their burrows, allowing them to be hand-picked and moved to a compost pile or other garden area.
It is important to avoid using harsh household chemicals like bleach, ammonia, or strong detergents that are sometimes suggested as home remedies. These substances are not only ineffective for long-term control but can also severely damage the turfgrass, disrupt the soil’s complex microbial community, and pose a threat to local wildlife.