Are You Buying Dead Fungi for Your Garden?

That “Helpful” Fungi You Bought for Your Garden? New Research Says It’s Probably a Scam.

If you’re a savvy home gardener, you’ve definitely seen the products. They come in slick packaging, covered in scientific-looking diagrams of plant roots. They promise to inoculate your raised beds with “beneficial” mycorrhizal fungi , creating a vast, symbiotic root network that will supercharge your vegetables.

This “magic” soil additive has become a billion-dollar industry , and it’s all built on a solid scientific premise: arbuscular mycorrhizal fungi (AMF) are amazing. They do form partnerships with most garden plants, acting as a secondary root system to fetch water and nutrients.

There’s just one problem. According to a pair of rigorous new studies from 2024 , the commercial products you buy in the store are, to put it bluntly, mostly junk. And in some cases, they might be actively harmful.

The 88% Failure Rate

First, let’s look at the big picture. Researchers at the University of Kansas (KU) published a meta-analysis in 2024 in the journal New Phytologist. They didn’t just test one or two products; they reviewed the data from 250 separate commercial product trials.

The result? In 88% of the trials, the products failed.

They either failed to colonize the plant’s roots at all, or they failed to produce any measurable benefit to the plant’s growth. That’s a staggering failure rate for an industry built on biological promises.

This analysis prompted the researchers to dig deeper. If the products aren’t working, why not?

Dead Spores and “Miracle” Fertilizers

For the follow-up study, the KU team (led by researchers Liz Koziol and James Bever ) tested 23 of the top-selling AMF inoculants available to consumers.

What they found explains the 88% failure rate.

  1. Many Products are dead: The fungi, which are living organisms, simply weren’t viable. The packages contained dead spores or, in some cases, no spores at all. As lead author Liz Koziol bluntly put it, “These fungi can do awesome things… But not when they’re dead”.
  2. The “Undisclosed Fertilizer” Deception: This is where it gets interesting. A few products did make plants grow bigger, but when the scientists looked at the roots, they found zero fungal colonization. The logical conclusion, supported by other research, is that these products are likely “spiked” with undisclosed chemical fertilizer. You, the gardener, think the “magic fungi” worked, so you buy it again. In reality, you just paid a massive premium for a pinch of conventional fertilizer that boosted plant growth without producing mycorrhizae.

The “Buried Lede”: You Might Be Buying a Plant Pathogen

This is the single most important finding of the new research, and it’s something every raised-bed gardener needs to know. The study didn’t just find ineffective products; it found contaminated ones.

Several of the most popular commercial inoculants were found to be contaminated with a plant pathogen called Olpidium.

Why is this a nightmare scenario for your garden?

The Olpidium resting spores, carrying the virus, can survive in soil for decades.

Let’s be perfectly clear: by adding one of these contaminated “beneficial” products, you could be paying to permanently infect your raised bed with a pathogen that vectors a crop-destroying virus.

An Unregulated Market

How is this possible? The KU researchers point out the obvious: the U.S. “fully lacks regulations” on the quality or safety of these products. Manufacturers are not required to prove their products contain what they claim, that the organisms are alive, or that they are free from pathogens.

Even one of the manufacturers, when confronted with the findings, admitted that they “welcome regulation” and have “seen the market flooded with products that have lots of claims that maybe do not go through the scientific testing to back them”.

What to Do Instead: Save Your Money, Use Native Soil

So, if the commercial products are a high-risk, low-reward gamble, what’s the solution?

It’s simple and free.

Remember the KU study? When they tested the commercial products, they got a 12% success rate at colonizing roots. But when they tested a control group—using soil from a local, undisturbed organic farm—they got a 72% success rate.

Your native, healthy soil is already full of local, adapted fungi 0 that are ready to work. The best thing you can do for your raised bed is to support them , not a product.

  1. Stop Buying the Powder: The 2024 research shows it’s likely a waste of money at best and a biological hazard at worst.
  2. Inoculate Natively: If you are starting a brand-new raised bed, don’t buy a bag of “magic” dust. Go to a local, established, healthy, chemical-free area—a friend’s organic garden, a local prairie, or a patch of forest—and take one or two shovelfuls of that soil to mix into your new bed. The 72% success rate from the KU study shows this is a far more reliable method.
  3. Stop Tilling: Tilling, even in a raised bed, “can destroy the developing soil structure” and shreds the delicate fungal networks (hyphae) you’re trying to encourage.
  4. Use Compost, Not “Miracle” Fertilizer: Avoid fast-acting synthetic liquid fertilizers, which “harm microbial activity”. Instead, top-dress your bed with high-quality compost, which has been shown to encourage and support native mycorrhizal colonization.

The promise of mycorrhizae is real, but the product is not the same as the promise. The best strategy, backed by this new 2024 research, is to trust the native, living soil you already have.

References

  1. Microbial Inoculants - ATTRA – Sustainable Agriculture - NCAT, https://attra.ncat.org/publication/microbial-inoculants/
  2. Soil health is big business, but KU researchers say many fungal …, https://eeb.ku.edu/news/article/soil-health-is-big-business-but-ku-researchers-say-many-fungal-products-dont-work-as-promised
  3. Understanding How Mycorrhizal Works and 10 Ways Your Garden Can Benefit from These, https://plantrevolution.com/blogs/news/why-need-mycorrhizal-in-garden
  4. Mycorrhizal Inoculants: The Path to Improving and Preserving Soil Carbon in Mainstream Agriculture - Groundwork BioAg, https://groundworkbioag.com/assets/uploads/2023/11/GW230303_WhitePaper.pdf
  5. ‪Liz Koziol‬ - ‪Google Scholar‬, https://scholar.google.com/citations?user=H8P1tgkAAAAJ&hl=en
  6. An assessment of twenty-three mycorrhizal inoculants reveals limited viability of AM fungi, pathogen contamination, and negative microbial effect on crop growth for commercial products | Kansas Biological Survey & Center for Ecological Research, https://biosurvey.ku.edu/pub/assessment-twenty-three-mycorrhizal-inoculants-reveals-limited-viability-am-fungi-pathogen
  7. James Bever | Department of Ecology & Evolutionary Biology, https://eeb.ku.edu/people/james-bever
  8. Pathogen Profile: Olpidium brassicae - Healthy Hydroponics, https://www.healthyhydroponics.ca/2023/08/24/pathogen-profile-olpidium-brassicae/
  9. Olpidium spp. - APS Journals, https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-10-12-0979-FE
  10. Role of Arbuscular Mycorrhizal Fungi in Maintaining Sustainable Agroecosystems - MDPI, https://www.mdpi.com/2673-8007/5/1/6
  11. Soil Inoculants | CAES Field Report - UGA, https://fieldreport.caes.uga.edu/publications/C990/soil-inoculants/
  12. Refreshing raised bed soil generates exceptional results - Illinois Extension, https://extension.illinois.edu/news-releases/refreshing-raised-bed-soil-generates-exceptional-results
  13. feed the soil: my experiment with mycorrhizae - A Way To Garden, https://awaytogarden.com/feed-the-soil-my-experiment-with-mycorrhizae/comment-page-1/
  14. Unravelling the synergistic effects of arbuscular mycorrhizal fungi and vermicompost on improving plant growth,nutrient absorption, and secondary metabolite production in ginger (Zingiber officinale Rosc.) - Frontiers, https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2024.1412610/full