What Do Active Earthworms Do for Soil?

Periods of Inactivity

• Earthworms aren't always active. They burrow deep into soil below the frost line and hibernate when it is extremely cold, waiting for warmer temperatures before rising to the surface again. They also take a siesta underground during summer if heat and drought are extreme. However, during this rest, called estivation, their metabolism doesn't slow as much as it does during hibernation. When they are active, earthworms are constantly busy improving soil.

Garden Benefits

• Flowers and vegetables grow better where there are lots of earthworms. The earthworms help create loam, which is a loose, well-aerated soil that is rich in nutrients. Earthworms drag organic litter from the soil's surface down into their burrows. As they eat the debris and the soil through which they tunnel, they excrete a compostlike material, called castings, that fertilizes the plants. The castings also chemically balance the soil's acidity and alkalinity, which helps garden plants thrive.

Lawn Improvement

• Lawn soil also benefits from earthworms. Aside from nourishing grass with their castings, earthworms prevent soil compaction that kills grass. Lawns with patchy areas that are hard and becoming bare usually suffer from compaction. This condition occurs when sod is poorly aerated or heavily trafficked such as school playing fields. Sod that contains plenty of earthworms is full of their tunnels, which help draw water and air to grass roots.

Remediation of Toxins

• Heavy metals such as arsenic are major soil pollutants in industrial areas. Scientists have been studying the beneficial effect of earthworms on these soils. The BBC News reported that researchers at Britain's Reading University in 2008 used earthworms to digest the toxins and change them in a way to allow plants to leach the substances from soil. Then the plants were either incinerated or harvested for furniture production. Earthworms weren't harmed by the toxins.

Negative Impacts

• Earthworms are generally beneficial. However, some eat the roots of shade-loving hosta plants in home landscapes. Others are overpopulating woodlands in Pennsylvania and Minnesota, where they are rapidly consuming organic litter on the forest floor that normally decays slowly and feeds trees and other forest plants. Earthworm castings also decrease soil acidity, which is a problem for acid-loving trees and forest plants.