The sudden appearance of dirt mounds disrupts the uniform appearance of a lawn and indicates activity occurring just beneath the turf, ranging from small insects to burrowing mammals. Effective removal begins with correctly identifying the culprit, as control methods depend entirely on the species involved. Understanding the visual signature each pest leaves behind guides the choice of intervention.
Diagnosing the Source of the Mounds
Accurate identification starts with examining the mound’s size, shape, and composition. Moles create conical or volcano-shaped mounds, featuring a circular, symmetrical pile of finely sifted soil. This soil is pushed up from a deep, vertical tunnel, often leaving a central plug marking the exit point. Mole activity also includes shallow, raised ridges or runways, which are feeding tunnels just beneath the surface.
Gophers produce crescent- or fan-shaped mounds where the soil is pushed out at an angle. The entrance hole is usually off to one side and plugged with soil, creating a flatter, asymmetrical profile. Gopher soil chunks are generally coarser than the finely textured dirt left by moles. Voles do not typically create mounds, instead favoring small, golf ball-sized holes and a network of above-ground runways appearing as narrow trenches in the grass.
Mounds from invertebrates are much smaller. Earthworm castings are small, granular piles of dark, rich soil, often described as crumbly or mud-like pellets, which are the worms’ nutrient-rich excrement left on the surface. Ant mounds are piles of very fine, granular soil; some species, like fire ants, create dome-shaped mounds without a visible central entrance.
Eradicating Mounds Caused by Subterranean Mammals
Trapping is the most successful method for removing burrowing mammals like moles and gophers. For moles, the strategy involves identifying the most active surface tunnels (raised ridges used repeatedly for foraging). An active tunnel is confirmed by flattening a small section and checking if the mole pushes the soil back up within 24 hours.
Effective mole traps, such as scissor, harpoon, or choker loop types, must be set directly into these active runs. After setting the trap, cover the area with a bucket or board to block light, as moles may avoid an open breach. Trapping is best performed in the spring and fall when moles are most active near the surface.
Gopher control relies on trapping, but traps must be placed in the main tunnel, not the surface lateral tunnels. Locate the main tunnel by probing the soil 10 to 12 inches away from the plugged hole of a fresh mound. Once located, two traps are typically set facing opposite directions to catch the gopher regardless of its approach.
Exclusion is a preventative measure for gophers and voles, involving burying a perimeter of hardware cloth or wire mesh at least 18 inches deep around vulnerable areas.
Repellents, particularly those containing castor oil, offer a non-lethal alternative to discourage moles from using your lawn. These products are applied to the soil to create an unpleasant taste and odor. The theory is that the castor oil makes their primary food source, earthworms, unpalatable, encouraging the moles to forage elsewhere. While not a guaranteed solution, this method requires thorough and repeated application across the entire affected area to maintain a deterrent effect.
Controlling Mounds from Earthworms and Insects
Earthworm castings are a management issue, not a pest problem, as the worms benefit soil health and aeration. Focus on cultural practices to minimize surface casting. The most practical physical control is dispersing the casts by sweeping or lightly raking them when they are completely dry. Brushing wet castings will smear mud across the turf, smothering the grass.
Cultural adjustments encourage worms to stay deeper in the soil. Earthworms are less active in well-drained, less organic-rich environments, so reducing excessive watering and collecting grass clippings limits their food and moisture sources. Altering the soil pH is an advanced technique, as worms prefer less-acidic soil, but this must be done carefully to avoid harming the turfgrass.
Ant mounds are controlled using a two-pronged approach combining slow-acting baits with targeted contact treatments. Granular baits are collected by foraging workers and carried back to the colony, eventually eliminating the queen and the entire nest. Baits should be applied when ants are actively foraging and should not be watered in, as moisture reduces palatability.
For immediate removal, a contact insecticide (granular or liquid drench) can be applied directly to the site. Raking the mound flat before application and watering the product in immediately helps the insecticide penetrate the tunnels. This method provides a quick knockdown of present ants but may not eliminate the queen, allowing the colony to rebuild nearby.
Restoring the Turf and Preventing Future Damage
After the source of the mounds is dealt with, the turf requires repair to restore a smooth grade. For small depressions or areas affected by castings, topdressing with a mixture of sand, compost, and topsoil is effective. Spread this mix in thin layers and work it into the grass canopy with a leveling rake or push broom to smooth the surface without smothering the grass blades.
For larger holes or ridges left by mammals, cut the damaged turf in a square or cross shape and peel it back to expose the disturbed soil. Fill this area with screened topsoil, tamped down to prevent settling, and fold the original turf back over the patch. Repair any bare spots by loosening the soil, scattering grass seed, and covering it with a fine layer of compost or topsoil to ensure good contact.
Long-term prevention focuses on maintaining a healthy lawn that is less attractive to pests. Removing grubs eliminates a food source that attracts moles and prevents severe turf damage. Proper moisture management means watering deeply and infrequently to promote deep root growth. Core aeration and soil testing address underlying issues like compaction or nutrient imbalance, helping the turf remain dense and resilient.