earthworms

Earthworms are active animals and feed by eating their way through the soil and bringing organic debris into their burrows from the surface. Research shows that in every 100 square feet of garden soil, earthworms may bring from 4–8 pounds of dirt to the soil surface each year. As earthworms tunnel through the soil, the soil is ingested and any organic matter is digested. Digested leaf litter (dead leaves and animals) contains nutrients made by plants during photosynthesis and includes calcium, nitrogen, potassium and phosphorus, and other organic minerals and nutrients.

Besides incorporating organic matter into your soil, earthworms are good manufacturers of fertilizer. Worm excrement, called castings, is deposited on the surface and is also rich in nutrients. Other animals and micro-organisms utilise these castings as food. Castings have a nutrient level and organic matter level much higher than that of the surrounding soil. The micro-organisms in the soil then break down this organic material. Each day they produce nitrogen, phosphorous, potassium and many micronutrients in a form that all plants can absorb. In this way, earthworms have helped produce the fertile humus that covers the land. 

A well managed, rich in humus soil can easily support 25 worms per cubic foot. This translates into at least 175 pounds of fertilizer per year for the same 200 square foot garden. For example, a 200 square foot garden with a low worm population of only 5 worms per cubic foot will be provided with over 35 pounds (about 1/3 pounds per worm) of top grade fertilizer by the worms, each garden year. Not only do they produce this fertilizer but spread it thoroughly within the top 12 inches of soil, and incorporate it as far down as 6 feet. This means that your garden or lawn can be supplied with far more superior quality fertilizer than 10–20 pounds of dry or granular fast acting chemical fertilizer. In fact, as the chemical fertilizer becomes soluble, it leaches into the soil and forces the earthworms to seek refuge elsewhere, thereby repelling those earthworms that are already present. 

Other contributions that earthworms make to your garden.

Adding calcium carbonate, a compound, which helps moderate soil pH. Over time earthworms help change acid or alkaline soils toward a more neutral pH. 

Their burrowing aerates the soil and loosen the soil, this is why earthworms are called “nature's plow”. They not only help bringing oxygen down into the soil, but their tunnel's allow rainwater carrying organic and inorganic nutrients down deep into the soil where the roots lie. The roots then take the water and the minerals and recycle them back to the herbaceous plants and woody trees. 

Finally, the tunnelling of the earthworms provides an access to deeper soil levels for the numerous smaller organisms that contribute to the health of the soil. The tunnels earthworms make beneath the topsoil do a tremendous service to the trees and plants above.

When earthworms die, usually in the dry summer, the organic material of their bodies is gradually released providing additional nutrients for plants. These minerals are essential to healthy plant growth.