Freezing and thawing of the soil during late winter and early spring also contributes to the roughness of lawns. Small castings left on the soil surface by earthworms also contribute to the roughness of lawns. While earthworms are partially responsible for the roughness of lawns, their activity improves the growing environment of the turfgrass plants. Earthworms improve the turfgrass environment by helping to decompose thatch. Their holes improve air and water movement in the soil.
Earthworms also improve soil structure.
The presence of a large number of earthworms in the yard and garden indicates fertile soils. The destruction of earthworms is not desirable nor feasible. Earthworms are beneficial and most pesticides registered for lawns and gardens will not kill earthworms. Good lawn care practices can help to alleviate the problems associated with rough, bumpy lawns. An application of fertilizer in the spring should thicken the turf and make the bumps less noticeable.