By Rebecca Ayres, Colorado State University Cooperative Extension Master Gardener, Denver County
More than fish bait or a snack for robins, the lowly earthworm determines the success of a garden as much as the gardener. Both the structure and fertility of garden soil are in the care of earthworms and plant growth depends on both.
Daily earthworms consume their weight in fallen leaves and other organic materials. They grind large particles into smaller ones. Soil microorganisms consume the small particles completing the conversion of once-living plants into living soil.
From spring until fall, earthworms burrow through the upper two feet of the soil. By day, they lie in burrows with their heads near the surface. On warm, damp nights, earthworms stretch out in search of food, using their tails to anchor themselves for a quick escape into their burrows.
Earthworm food includes leaves, seeds and grass clippings. The plant debris is pulled into the burrow where the soft parts are eaten with soil particles to grind the food. Another use for plant debris is to plug the burrow against moisture loss on hot days.
Earthworms literally eat their way through the earth. Tunneling is accomplished by forcing themselves into small cracks, swallowing soil and debris that get in the way. Feeding is accomplished at the same time as tunneling. The maze of tunnels allows water and air to penetrate the soil.
The other way earthworms improve soil is through their feeding. Soil and plant debris are bound together into crumbs as they pass out of earthworms, improving soil structure. Soil structure refers to the arrangement of soil particles. Fine particles of clay soils pack close together, impeding water and air penetration. The larger soil crumbs produced by earthworm feeding increase the space available for air and water between soil particles.
The plant debris passed through earthworms is broken down into the original nutrients used to build the now-dead plant. Many nutrients, such as nitrates, phosphates and potash, are immediately released into the soil while other nutrients are released gradually. The earthworm's activity is like a miniature composter that mixes and conditions plant wastes into fertilizer for new plants.
In addition to improving soil structure and fertility, research has found soil rich with earthworms hosts fewer parasitic nematodes. Earthworm activities directly stimulate beneficial organisms that trap, ear and out-compete plant-eating nematodes.
Several garden practices encourage earthworms. Mulching creates a cool, moist environment favorable for earthworms. They will not tolerate soggy soil, are very sensitive to light and must have damp skin to survive. Finished compost mixed into the topsoil encourages earthworms as does the food provided by a grass or leaf mulch.
Planting fall cover crops such as clover or winter rye, and tilling them into the soil in spring, also will increase earthworm numbers. Leaves spaded into the soil during fall soil preparation will be eaten by earthworms and enrich the soil.
Earthworms feed during the cool of the night and a light sprinkling of corn meal on the surface of the soil can promote rapid reproduction. Earthworms also will assimilate kitchen waste such as coffee grounds, vegetables and fruits lightly tilled into the soil.
Many gardeners measure the health of their soil by the number of earthworms. Studies have shown that active worm populations boost plant production. According to United States Department of Agriculture information, an acre of land can host up to 500,000 earthworms that move up to 5 tons of soil in a year.
With a life expectancy of 10 to 15 years, earthworms are more productive in the garden than at the end of a fishhook.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010