I often get calls from homeowners describing their lawns having a soft spongy feel when walking on it and with hundreds of tiny mounds of dirt pushed up everywhere. After a few minutes of discussion describing the size and condition of these tiny piles of soil the conclusion usually is that they are the castings of earthworms. In most cases there should be no reason for alarm as earthworms in moderate numbers are beneficial to the lawn as they tunnel through the soil providing pore spaces for air, water and nutrients to move freely helping develop healthy turf with a strong root system. Occasionally, however, their numbers increase tremendously especially with ideal moisture conditions and the castings become so numerous that they can create a muddy situation that distracts from the beauty of the lawn as well as tracking of mud into the house. High numbers of earthworms may also attract moles and armadillos onto the lawn to feed on them creating more serious tunneling and digging. While no one advocates applying insecticides to control earthworms since they are so beneficial some products that are used to control grubs and other soil dwelling insects can suppress earthworm populations. The best advice though is that if they are not creating any serious problems then consider these tiny mounds of soil as nothing more than nature’s fertilization and soil conditioning.
Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. firstname.lastname@example.org