By Carrie Knutson, NDSU Extension Agent, Grand Forks County

Gardening lessons are always a highlight of my summer programs.

This year when I asked the gardeners what they wanted to learn about for their last lesson, worms were the undisputed winner. Earthworms are a beneficial garden creature that many of us take for granted.

We have thousands of different types of earthworms. The scientific classification could be and probably is a college course. Earthworms belong to the animal kingdom and phylum Annelid. To prevent information overload, I will stop there with earthworm scientific classification.

Instead, let’s look at how earthworms are classified based on the soil environment in which they live. Deep-burrowing species, represented by the common night crawler, construct permanent burrows as deep as 4 to 6 feet in the soil. They feed on soil and organic debris on the soil surface and convert it into humus.

WDAY logo
listen live
watch live
Newsletter signup for email alerts

Upper soil species build wide-ranging, mainly horizontal burrows. Their burrows are not permanent. They feed on mineral soil particles and decaying organic matter. As they move through the soil, they mix and aerate the soil and incorporate minerals into the topsoil.

Surface soil and litter species, such as the common red wiggler, usually are found in areas of rich organic matter such as the upper topsoil layer, under piles of leaves or decaying logs, or in piles of manure. These worms adapt easily to vermicomposting systems because they don’t burrow deeply into the soil and prefer rich organic matter.

Earthworm activity has a deep impact on soil health. Their activity improves soil aggregation. Soil aggregation is a natural process in which the soil particles are bound together.

The burrows created by earthworms can be a major channel for soil water movement. The added channels and increased soil aggregation improve soil porosity.

An increase in porosity will improve drainage, reduce compaction and help roots get the air they need for healthy growth.

Earthworms are great composters. They consume large amounts of organic matter and incorporate it into the soil.

Creating a garden that is friendly to earthworms is easy to do. Start by reducing the amount of tilling you do, disturbing the soil as little as possible.

Second, leave plant residue on the surface of your garden to feed the earthworms. This can be mulch, compost or disease-free plant residue. Covering the soil also will help reduce the amount of weeding and tilling you need to do.

Finally, only use pesticides when necessary because pesticides can be toxic to earthworms. Happy gardening!

For more information about gardening, contact your local NDSU Extension agent. Find the Extension office for your county at https://www.ag.ndsu.edu/extension/directory/counties.