Increase your garden soil productivity with earthworms

For many years, farmers and gardeners prioritized the chemical and physical properties of soils in which plants were grown over the biological properties of these soils. Thankfully, we have learned over the past couple of decades about the overarching importance of the biological properties of farm and garden soils, including the importance of earthworms in garden and farm soils.

Earthworms provide many benefits to healthy, productive soils, and wise gardeners do everything they can to maintain healthy populations of earthworms in the soils they tend.

Earthworm species

There are many different species of earthworms throughout the world, with the ubiquitous night crawler (Lumbricus terrestris) being the most common species in garden soils in Greater Columbus. These denizens of the deep are not native to the United States and were likely accidentally introduced to North America by European settlers in the soil of plants they brought with them to the

New World, and in the ballast of the ships on which they traveled.

Many species of earthworms native to northern areas of the United States died out during the Ice Age, but some species survived and evolved in the unglaciated areas of southern states. While beneficial, night crawlers are considered invasive and have replaced native species of earthworms in some unglaciated parts of the United States.

The importance of earthworms

Approximately 50% of the volume of a healthy living soil should be pore space available for storage and movement of water, oxygen and other gases. Earthworms burrow vertically deep in the soil, creating tunnels which serve as pore space in the soil. These tunnels are especially important in soils that are compacted and lack adequate pore space. These tunnels also help drain soils during periods of excess soil moisture.

Earthworms also provide soil nutrients essential to plant growth by consuming organic matter and producing castings (excrement) that contain several nutrients used by plants including nitrogen, calcium, phosphorous, potassium, and magnesium.

Soil structure refers to the way particles of the soil - whether sand, clay, or silt - are grouped together. Earthworm castings cement or bind the soil particles together and create heavier lumps called aggregates. Heavier soil aggregates reduce soil erosion, decrease soil and nutrient loss due to runoff, and improve root penetration, moisture retention, and soil drainage.

Earthworms can also improve soil health as their castings provide a food source for soil microbes, which serve as the foundation of the food web in the soil. Earthworms also serve as an importance food source for certain wildlife including birds, moles, voles, and even raccoons and skunks.

Earthworm populations are usually highest in places with moist, loamy soil. They often aren’t present in sandy soils because these soils dry out very quickly and force worms to either go deeper into the soil where they could die or enter diapause (hibernation) until conditions improve. Sandy soils also have a tendency to be low in organic matter that serves as a food source for earthworms.

If you want worms to stick around in your garden, adding organic matter in the form of compost, composted manure, or other types of organic matter can help improve soil moisture-holding capacity and provide a food source for earthworms.

Additionally, reducing tillage and adding an organic mulch to the surface of the soil can improve earthworm habitat. Properly fertilizing and liming based on soil test results is beneficial, as worms are more likely to inhabit soils that are slightly acidic to neutral.

Finally, research has also shown that excessive use of synthetic chemical pesticides can reduce earthworm populations.

Adding earthworms to garden soils

While earthworms and earthworm eggs can be purchased online and at garden centers and added to garden soils, providing the proper soil conditions needed for earthworms to thrive naturally is of greater importance than augmenting existing populations of earthworms.

Earthworms can be added to raised beds so long as beds are not elevated and do not have a solid bottom separating the topsoil from the native soil, preventing earthworms from burrowing deep into the soil beneath the raised bed.

Earthworms play an important role in maintaining the productivity of garden soils. This makes understanding these lowly animals and finding ways to make them thrive critical to the sustainability of garden soils.

Mike Hogan is an extension educator, Agriculture and Natural Resources, and associate professor with Ohio State University Extension.

hogan.1@osu.edu

GETTY IMAGES A young boy has been digging in the garden and found several earthworms.

PROVIDED Earthworms are usually found in places with moist, loamy soil.

OSU EXTENSION Earthworms provide many benefits to healthy productive soils.