Earthworms have been called “nature’s plows” for the way they dig through the soil. Their tunnels help aerate and loosen the soil, making it easier for plant roots to penetrate well below the surface, and along the way they drop their poop, a rich fertilizer called a casting. See how to attract worms to the garden!
When the frost leaves the ground, the earthworms start moving upward in the soil looking for mates. While you are cleaning up the leftover leaves and debris from your garden this spring, look closely and you might see one disappearing back into the ground.
The channels created by worm activity enhance the ability of water to percolate into the soil instead of running off, reducing erosion. An important part of our global soil ecosystem, earthworms have been around for about 300 million years. They are so widely found that we think of them as native to our soils but most of the original native earthworms found in cold climates such as the northern US and Canada were killed off by the glaciers. The abundance of worms we now have were introduced, either on purpose or accidentally, by settlers in the plants and soil they brought with them from Europe.
There are thousands of species of earthworms worldwide but most fall into one of three groups.
- Litter dwellers live in crop debris and leaves, not in agricultural soil. Manure worms and redworms used in vermiculture are in this group. See how to start vermicomposting and use worms to turn kitchen scrapes into fertilizer!
- Topsoil dwellers live in the upper 2 to 3 inches of soil, eating dirt and organic matter found mixed in the soil. They create horizontal burrows which they fill with their castings.
- Subsoil dwellers, such as nightcrawlers, create vertical burrows that can reach 5-6 feet straight down into the ground. They deposit their castings on the surface outside their burrows.
When Worms Go Bad
In some situations, earthworms can be harmful to the ecosystem. Forests have been harmed by overzealous worms that have moved in and eaten up all the leaves and debris that naturally fall to the forest floor. The trees and native wildflowers that live there evolved without any worms and they actually need that layer of debris for their seeds to germinate and grow.
Intestines of the Earth
As they burrow through the soil, earthworms eat everything in their path. They can process a lot of soil, eating two tons of dry matter per acre in a year, digesting it and mixing it with soil to form castings. Some worms also devour nematodes which can be harmful to plants. Since a worm’s gut contains a multitude of microorganisms, what comes out can have 8 times the nutrients of what went in! Castings contain humic acid which can control plant pathogens while stimulating healthy plant growth and they have a neutral pH. A mixture of organic matter and minerals, castings are also rich in nitrogen, phosphorus, potassium, calcium, iron, magnesium, and sulfur in a soluble form that plants can readily use. An earthworm can produce its weight in casts per day.
A pile of castings outside a burrow.
Let’s Count Worms
The presence of worms in your soil is an indicator of a healthy garden. If you are interested in learning how your garden stacks up here’s an easy way to test it.
Dig up a section of ground 12 inches by 12 inches and about 6 to 7 inches deep. Place the soil on a tarp and count the number of worms in the sample. If you find ten or more you have a healthy population. No worms at all? It means that the conditions must be poor - no moisture, toxic substances, sandy soil, or no organic matter for them to eat will all prevent them from setting up shop in your yard.
What a Worm Wants
If you want to encourage or sustain a healthy population of worms there are a few things you can do to improve the conditions for them:
- Reduce tilling your soil.
- Leave organic matter on the surface.
- Add manure and compost.
- Ditch the chemicals.
- Use an organic mulch to keep soil moist and cool.
Soil environment affects population. Simply adding worms to a to a poor environment won’t work. They need the right conditions to prosper.
- Water. Earthworms need moisture to live since their bodies are 80% water, but because they breathe through their skin, too much water can drown them.
- Soil Texture. They prefer loamy soil. Overly sandy soil is abrasive and dries out too quickly.
- Acidity. They prefer a neutral pH of 7 but will tolerate 5 to 8.
- Temperature. Earthworms are cold-blooded so 50 to 60 degrees is optimum. Populations fluctuate naturally with the seasons. Adults die off in the summer and young ones hatch out in the fall. Over the winter they burrow deep below the frostline. Some species winter over as eggs and hatch out in the spring.
If you want a better garden, be kind to your worms!