Human Health Benefits of a Healthy Soil Microbiome

Okay, hear me out. That dirt on your hands after a morning in the garden? It might actually be good for you.

I know how that sounds. We've spent decades being told that germs are the enemy and that clean hands are healthy hands. Sanitize everything. Wash it all off. Don't let the kids eat dirt. (Guilty — I definitely panicked the first time my daughter did exactly that. It's actually why I started this whole company, but more on that in a second.)

The thing is, science is telling a really different story right now. Your garden soil is alive — billions of bacteria, fungi, and other microorganisms all working together. And a lot of them? They have a direct, measurable impact on human health. Your immune system. Your mood. Your gut. Even your kids' long-term risk of developing allergies and asthma.

This isn't fringe stuff. Researchers at major universities around the world are publishing on this. So let's dig in (yes, pun intended) and talk about what's actually living in healthy soil — and why the people tending it are benefiting in ways most of us never even thought about.

The Soil Microbiome: A Living World Beneath Your Feet

Here's a number that still blows my mind: a single teaspoon of healthy garden soil can hold up to one billion bacteria. Plus hundreds of meters of fungal threads, thousands of protozoa, and a whole lot of other stuff we're still figuring out. That's more microorganisms than people on this planet. In a teaspoon.

This whole community is what scientists call the soil microbiome. And just like the gut microbiome you've probably heard about, it thrives on diversity. The more different species living together in your soil, the more resilient and functional that ecosystem is. And — this is the part I really want you to sit with — the more beneficial it is to the humans spending time in it.

When I started Elm Dirt, I had our products tested by BiomeMakers, one of the leading agricultural microbiome labs in the country. Our Plant Juice came back with 291 lab-verified microbial species. Bacteria and fungi you'd find in the healthiest, most productive organic gardens anywhere. That report genuinely changed how I thought about what we were doing — not just for plants, but for my family. You can learn more about what living soil actually means if you want the full picture.

The Specific Microbes That Actually Benefit Human Health

I'm not going to do the vague "nature is good for you" thing here. Let's talk actual microbes, actual mechanisms, actual research. Because once you get into the specifics, this stuff is genuinely fascinating.

Mycobacterium vaccae: The Mood-Booster Hiding in Your Garden

Mycobacterium vaccae is probably the most surprising discovery in all of soil-human health research. It's a completely harmless bacterium that lives naturally in garden soil. And when you touch it — or even just breathe it in — something remarkable happens in your brain: your body starts producing serotonin.

Researchers at the University of Colorado found that M. vaccae activates the same neural pathways as antidepressant drugs, specifically by stimulating serotonin-releasing neurons in the prefrontal cortex. (Lowry et al., 2007, Neuroscience). A follow-up study found it also reduces anxiety and improves cognitive function under stress. (Smith et al., 2019, PNAS).

So that feeling you get after a few hours in the garden — that calm, contented, almost meditative thing — it's not just in your head. Well, it is literally in your head. But there's actual biology behind it. You're absorbing a natural serotonin trigger through your hands.

Pseudomonas putida: The Toxin Fighter You Didn't Know You Needed

Pseudomonas putida is one of the most well-studied beneficial soil bacteria in existence, and we confirmed it's in our Plant Juice (BiomeMakers CUX005, May 2024). In soil, it breaks down environmental toxins — including pesticide residues — which is a big deal if you're gardening in a space that's had any synthetic chemical history.

But the human health angle is what's really interesting. Certain Pseudomonas species appear to help modulate inflammatory responses, and they actively compete against pathogenic bacteria in both soil and gut environments. Their presence is associated with healthier, more balanced microbial communities overall. (Tringe et al., 2020). We actually did a whole deep-dive on Pseudomonas as a soil superhero — worth a read.

Lactobacillus: Wait, the Probiotic Bacteria Is in Soil Too?

Yep. The same bacteria you find in yogurt and probiotic supplements also lives in healthy garden soil. We confirmed multiple Lactobacillus species in our Bloom Juice (BiomeMakers CUX004, 2022) — including Lactobacillus delbrueckii, Lactobacillus pentosus, and Lactobacillus vaccinostercus.

Here's why that matters: when you grow vegetables in living, Lactobacillus-rich soil, those bacteria transfer from the soil to the plant. And then into your gut when you eat. Research published in Frontiers in Microbiology confirmed that this soil-to-gut microbial transfer is a real, documented pathway — and one that essentially disappears when food is grown in sterile, chemically managed conditions. (Blum et al., 2018). We did a full breakdown on Lactobacillus in soil if you want the whole story.

Flavobacterium: Immune System Training, Straight from the Garden

Flavobacterium is one of the dominant genera in our Plant Juice formula — confirmed at 2.22 million cells per gram. It's well known in soil science for nitrogen cycling and organic matter breakdown. But the human health connection is newer and genuinely exciting.

Flavobacterium species appear to help "train" the human immune system. Their cell wall components — called lipopolysaccharides — are recognized by immune cells and trigger a calibration response. Basically, regular low-level exposure to this kind of bacteria keeps your immune system sharp and appropriately tuned. It's a big part of what researchers call the biodiversity hypothesis — the idea that contact with a diverse range of environmental microbes is what keeps immune systems from overreacting to things that aren't actually threats. (Rook et al., 2003, BMJ).

Mortierella: This Garden Fungus Produces Omega-3s

Okay, this one genuinely surprised me the first time I read it. Mortierella is a beneficial soil fungus — we confirmed multiple species in both Plant Juice and Bloom Juice — and Mortierella alpina in particular is actually the commercial source of ARA (arachidonic acid) used in infant formula. It's one of the only land-based organisms that naturally produces omega-3 and omega-6 fatty acids.

When Mortierella is thriving in your garden soil, it contributes to a richer overall soil environment. Plants grown in fungal-rich soil develop stronger cell walls and higher nutrient density — so the vegetables you're eating out of your garden are genuinely more nutritious than the ones grown in depleted soil. The research is still developing, but check out our post on Mortierella and mycorrhizal root health for the science. (Partida-Martinez, 2020).

Trichoderma: The Fungal Bouncer of Your Garden

Trichoderma harzianum and Trichoderma piluliferum — both confirmed in our Bloom Juice BiomeMakers analysis — are widely used in organic farming because they're incredibly aggressive against harmful fungal pathogens. They basically out-compete the bad guys so thoroughly that disease just doesn't get a foothold.

The human health angle here is more indirect but still real: when Trichoderma is keeping pathogenic fungi in check, it reduces the overall load of harmful fungal spores in your garden environment. If you or anyone in your family has mold sensitivities or a compromised immune system, that matters. Gardening in Trichoderma-rich soil is a physically healthier experience — not just for your plants. It's also one of the reasons fungi-rich soil does so much more than most people realize. (Harman et al., 2004).

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Thomas J. — Verified Buyer

"When I transplanted my strawberries, I gave them a light dose. The following week I gave them a full dose. In 3 weeks they went from small runners to blooming healthy plants. First time they grew this fast in years."

The Hygiene Hypothesis: Why Your Kids Actually Need to Get Dirty

If you have kids — or grandkids, or you're just thinking about the next generation — this section is for you. Because one of the strongest arguments for keeping your soil alive and healthy isn't about your tomatoes. It's about their immune systems.

The hygiene hypothesis (scientists now prefer calling it the "old friends" hypothesis, which I think is much more charming) says that the explosion of allergies, asthma, eczema, and autoimmune diseases in developed countries is directly tied to our loss of contact with diverse environmental microbes. We're too clean. Our kids spend too much time indoors. Our food is grown in sterile, managed soil. And our immune systems — which evolved to be constantly trained by microbial exposure — are essentially going rogue because they've run out of real threats to calibrate against. So they start attacking pollen. Peanuts. Pet dander.

A landmark study in Science found that kids who grew up on traditional farms — with regular exposure to soil and animals — had dramatically lower rates of asthma and allergies than urban kids. (Stein et al., 2016). Another found that children in areas with higher soil microbial diversity had significantly lower rates of type 1 diabetes. (Vatanen et al., 2016, Cell). And our post on how growing organic increases polyphenols gets into how this carries through to the actual food your family eats.

Here's the Part That Gets Me Fired Up: Synthetic Fertilizers Kill All of This

Every single benefit we just talked about — the serotonin boost from M. vaccae, the immune training from Flavobacterium, the gut-soil microbe transfer via Lactobacillus, the Mortierella omega-3s — none of it works if the soil is dead.

And that's exactly what synthetic fertilizers do over time. They bypass the soil biology entirely and feed the plant directly. Which sounds efficient, until you realize you're essentially starving the ecosystem those benefits depend on. Worse, many synthetic fertilizers — especially the high-salt ones — actively kill the beneficial microbes we've been talking about. Repeated NPK applications can sterilize soil over years, leaving you with a chemically dependent growing medium that produces nutrient-poor food and gives you zero microbial benefit.

This is why I started Elm Dirt. I'm a chemical engineer — I genuinely understand how these compounds behave. And when my daughter ate dirt from our garden (terrifying in the moment, clarifying in retrospect), I started looking hard at what was actually in the soil my family was living around. What I found made me uncomfortable. The move to living, microbial-rich inputs wasn't just about better plants. It was about not quietly destroying the invisible ecosystem my family's health depends on.

If you want to go deep on this, our Synthetic vs. Organic Fertilizers breakdown lays it all out, our 5 Reasons to Stop Using Synthetic Fertilizers makes the case simply, and our living soil vs. sterile soil post shows the difference side by side.

So What Do You Actually Do About It?

Good news: building a human-healthy soil microbiome isn't complicated. It just takes a few consistent habits and the decision to stop working against your own biology.

Stop killing what's already there. Synthetic herbicides, pesticides, and fertilizers all disrupt microbial communities — even the ones marketed as "safe." You genuinely cannot build a thriving soil ecosystem while simultaneously nuking it. If you're not sure where to start, our chemical-free gardening guide walks you through it.

Feed your soil consistently. Compost, worm castings, leaf mulch — these are the food source for your soil microbiome. Our Ancient Soil worm castings carry Class A compost certification and are packed with the organic matter beneficial microbes actually need. The science behind them is pretty cool too — see our posts on worm casting science and what worm castings actually are.

Inoculate with living microbial inputs. This is where Plant Juice comes in. With 291 third-party verified microbial species — including Pseudomonas putida, Flavobacterium, Mortierella, Trichoderma, Lactobacillus, and a whole lot more — it's basically a probiotic for your garden. You're not just feeding your plants. You're actively populating your soil with the organisms that make all of this possible.

Skip the tilling. Tilling tears up fungal networks and kills off beneficial communities that took months to establish. Wherever you can, lean into no-dig methods. We wrote about no-dig gardening for healthier soil if you want to explore that approach.

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Chris V. — Verified Buyer

"Look at all the new growth on my Apple tree using Plant Booster. The roots were damaged from shipping to transplant. Wow it healed them up quick. I was real worried about the health of my Tree!!! All Better!!"

The Big Picture: Soil Health and Human Health Are the Same Thing

There's a quote I keep coming back to. Sir Albert Howard wrote in 1940: "The health of soil, plant, animal, and man is one and indivisible." He wrote that before we had the microbiome science to back it up. Before BiomeMakers existed. Before we could sequence 291 species from a bottle of liquid fertilizer. And he was exactly right.

The food on your table is only as nutritious as the soil it came from. The air in your garden carries microbial signals that change your brain chemistry. Your kids' immune systems are being shaped right now by the diversity of microbes they encounter — or don't. And your gut health, which research links to everything from mental health to cardiovascular risk, is connected to the microbial richness of the environments where your food is grown.

None of this requires perfection. It just requires being a little more intentional. Choosing organic inputs. Building living soil. Not panicking when your kid has garden dirt under their fingernails — and maybe secretly hoping they do.

If you want to keep going down this rabbit hole, our post on human health and soil health goes even deeper into the research, and our microbe fertilizer science post explains how living inputs actually work at the biology level. Brand new to all of this? Start with our beginner's guide to organic fertilizer — it's written for real people, not scientists.

Start Growing a Healthier Garden — and a Healthier Family

The science is clear on this. The soil microbiome isn't separate from human health. It's part of it. Every time you tend your garden with living, organic inputs instead of synthetic ones, you're doing something genuinely good for your family — not just your plants.

If you're ready to start, Plant Juice and our Ancient Soil worm castings are where we'd point you first. They're what we use in our own garden — with our own kids running barefoot through it. That's not a sales pitch. That's just honest.

Happy gardening.
— Lauren & the Elm Dirt team

Lauren Cain — Founder & Chemical Engineer, Elm Dirt

Lauren started Elm Dirt after her infant daughter ate dirt from their garden and she realized she had no idea what was in it. As a chemical engineer and mom based in Grandview, Missouri, she set out to build fertilizers around living soil biology rather than synthetic inputs — products she'd actually feel good about her kids being around. Today, Elm Dirt is used by home gardeners, rose champions, and certified organic growers across the country.