Soil Health Diagnostics Series

This article is a part of a series of aggregated information about soil health indicators.

• Wild Plant Indicator Species

Who’s Living in Your Soil?

It can be easy to think of your garden soil as nothing more than stagnant dirt.

But the reality is, soil is very much a living, breathing system. Soil is full of life - both on a microscopic level and with creatures and fungi that we can see with the naked eye.

Just like humans, these species have needs. They display feedback loops within their habitat. They are stronger in their diversity, which helps to create a more stable and robust system.

The creatures we can see — animals like earthworms, insects, and isopods -- are macroinvertebrates. No microscope required for these guys!

What do soil creatures have to do with soil health?

According to the Xerces Society, certain indicator species are very sensitive to different soil conditions.

When you notice their presence, you get valuable information about the soil conditions in your yard.

Here are three things that I find most interesting about soil indicator species:

1. Climate Change Mitigation: As a regenerative gardener, it’s fascinating to think about the connection between certain soil invertebrate populations and soil carbon sequestration levels. More on this later!
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2. Regenerative No-Till Benefits. Most of the time, beneficial soil fauna live in undisturbed soil with healthy levels of organic matter. There are a couple of instances where this is not the case though, but the good news is that there are solutions!
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3. Correspondences to Plant Stress. Have you ever noticed aphids are attracted to older broccoli plants? While aphids aren’t soil-dwellers, their presence indicates environmental stressors on plants. Another example of this is the mealybugs -- they can point to a nitrogen over-fertilization issue.

Soil Invertebrate Indicator Plant List:

In the interactive table below, you’ll be able to find out what certain soil-dwelling macrofauna indicate about the health of your garden soil. It’s sortable so you can arrange the invertebrate list in forwards or reverse alphabetical order for ease of reference.

Take a look — do any of these garden visitors look familiar? What do they have to say about your soil’s state?

My Garden’s Soil Life Population: Increase in Beneficial Invertebrates With Regenerative Practices

When I first started my garden, I was growing on uncultivated land. I thought a truckload of compost would bring life to some raised beds. However, I once I realized that I had hardly any macrofauna in my soil, I was pretty disappointed. For example, there were hardly any earthworms at all. We had no signs of ground beetles or much else --  besides slugs.

I took a “build it and they will come” approach. I focused on building up the soil with regenerative approaches like mulching, cover crops, and chop-and-drop.

By the second growing season, I started to notice something exciting - earthworms! And even better - their castings, scattered around in tiny clusters. This helped me to know that I was on the right track with my soil health efforts.

Fast forward to my garden’s fourth growing season. This was when I started to see a greater population and diversity in soil life. Now, I had ground beetles in high numbers, which helped balance out that slug problem. Small spiders in huge numbers made home in the straw mulch, and I started to notice pot worms and centipedes, too.

Another exciting revelation was that I now not only had earthworms in my garden, but red wigglers too! These worms show up when there’s a lot of decaying matter - like goat manure and bedding - on the surface of the soil. Worm biodiversity indicates a well-balanced soil system.  I really couldn’t be happier to have these friends making their home in my yard!

This experience showed me something that I could see clearly with my own two eyes. The regenerative practices turned my garden into a living, breathing ecosystem.

Curious about how to replicate these results in your own garden? Here are some tips below to get you started.

Practical Tips and Techniques for Encouraging Soil Macrofauna

With a few thoughtful action steps, you can transform your soil into a happy and healthy habitat.

1. Start No-Till Gardening. Avoiding traditional tilling to you maintain the delicate structure of the soil. This allows macrofauna like earthworms and beetles to flourish without disruption. Plus, you'll keep carbon sequestered in the soil with a rich microbial community.
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2. Incorporate Cover Crops. Cover crops like clover or vetch can improve soil structure, enhance organic matter, and provide a habitat for beneficial macrofauna. As cover crops decay, they become a living mulch that enriches the soil naturally.
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3. Add Organic Matter. Regularly top-dress garden beds with well-rotted compost, leaf mold, or aged manure. This organic material feeds the soil organisms, improves soil texture, and boosts water retention.
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4. Control Moisture Levels. Ensure your soil stays consistently moist, but not waterlogged. Macrofauna need moisture to survive, so regular watering during dry spells important.
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5. Plant Biodiversity. Diversify your plantings with companion plants and intercropping. Different root structures and nutrient needs balances soil nutrients and attracts a wider array of beneficial insects.
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6. Avoid Chemical Interventions. Minimize the use of chemical fertilizers and pesticides. These inputs can harm beneficial soil organisms. Instead, focus on natural pest control methods and organic fertilizers.

A Special Note on Earthworms

According to Pulleman et. al, we can observe three groups of worms in healthy soil.

Each group provides a slightly different ecosystem service.

1. Anecics (i.e. common earthworms, Lumbricus terrestris). Live in burrows and feed on the soil surface. Seeing common earthworms in your garden is a sign that your no-till practices are paying off.
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2. Epigeics (i.e. red wigglers, compost worms in the Eisenia genus). Found on the surface layer of the soil, this group shows up where organic matter levels are high. They feed on plant littler, so populations increase with regenerative techniques.
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3. Endogeics (i.e. common grey worm or rosy-tipped worm in the Aporrectodea genus). Present when the other two groups are also living in the soil. Their populations increase in no-till systems.

There's one thing most people miss when observing worms in their soil. While worms themselves are a signal of soil health, it’s even better to have different groups of worms in your garden.

One thing most people miss when observing worms in their soil is that while worms themselves are a signal of soil health, it’s even better to have different groups of worms in your garden. As the authors of this study say, this is “a better proxy for habitat quality and soil functions.”

The Irony of the Garden Symphylan

Remember how I mentioned earlier that usually regenerative practices help repel pest species?

There’s an infamous instance where this isn’t the case: The Garden Symphylan.

As John B. Cobb says, “there are always exceptions to every generalization.”

You see, while soil “good guys” like worms, beetles, and springtails are signs of a vibrant ecosystem...

...the “pest” species of garden symphylans are too.

Don’t lose hope of maintaining a regenerative garden if you find this pest in your soil!

You will be happy to know that targeted regenerative solutions can reduce the severity of an infestation.

Here’s what the experts recommend:

1. Crop rotation. After brassicas and beets, grow potatoes. Populations can reduce in potato plantings (ATTRA).
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2. Grow out transplants. Crops are most vulnerable to symphylan damage when they are newly germinated. Start seeds in modules and transplant out after 1-3 months, potting up if necessary (ATTRA).
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3. Reduce organic matter input. While it pains me a bit to say this, University of California recommends reducing manure input and organic matter additions. This is especially relevant if the material is not fully broken down (UC IPM).
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4. Promote beneficial insects. Predatory mites, ground beetles, and centipedes will eat symphylans. Beetle banks and attractive herbs can create a more balanced ecosystem (UC IPM).
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5. Avoid monocropping: On the Permies forum, Ben Zumeta tells of farmers who spoke at the Sustainable Food and Farming Conference in 2020. They noticed that symphylans did the most damage when one crop was in one row. Populations decreased in mixed crop species plantings.
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6. Add wood chips to pathways and increase fungal diversity: There’s a suggestion by Dr. Elaine Ingham, soil scientist, that increasing your soil’s fungal hyphae can prevent symphylan crop damage. Ben Zumeta mentioned that the farmers noticed less damage where they had mulch with wood chips. Teaming with Fungi by Jeff Lowenfels might be a good resource if you’d like to learn more about fungi in soil.
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7. Plant in successions: Ben Zumeta lso notes that farmers would stagger their crop plantings throughout the growing season. In this way, any damage did not wipe out the full crop.

Soil macrofauna signal soil carbon levels

In regenerative gardening and agriculture, we focus so much on soil health. This isn't only because it helps us to grow healthier plants. There's an added bonus - the soil can store more carbon. The soil moves carbon from the atmosphere into the earth. This means we can mitigate climate change in our own backyards.

One interesting way to think about soil-dwelling invertebrates is as “carbon eaters.” They feed on carbon sources in the soil  (Prinandhika et. al).

How do they get their sources of carbon? Indirectly, it’s through the photosynthesis of plants.

How do they get their sources of carbon? It’s through the photosynthesis of plants.

Think about organic matter souces like fallen leaves, cover crops, and chop-and-drop systems. During photosynthesis, these plants take carbon out of the air and store it in their tissues. As they break down, the carbon gets moved into the soil.

Soil fauna process these materials. They actually help bring the carbon deeper into the soil, so it becomes more stable.  No-dig practices keep that carbon in the soil. In contrast, tillage causes the carbon to “escape” into the atmosphere (Prinandhika et. al).

Say Hello to the Livestock You Didn't Know You Had: Soil Macrofauna

Gardens offer an opportunity to form deep connections with the earth. Your observations of soil macrofauna provide a lot of information about the habitat you're creating.

In my gardening journey, I've noticed that a supportive habitat for soil creatures leads to a more vibrant garden. To foster an ecosystem that thrives benefits all aspects of garden life.

Regenerative gardening principles encourage us to work in partnership with nature. In this way, we can enhance the resilience of our gardens and support broader ecological balance.

Further Resources

• Xerces Society has a helpful printable sol bioindicator guide that you can print out for reference
• Nerd out with the research of Dr. Patrick Lavelle, a leading scientist in the field of soil fauna indicator species. Read some of his fascinating studies here.
• Learn how to survey soil life with this article from SARE, or dive even deeper into the world of the soilbiome with their free 120+ page PDF on farming with soil life.