Mycorrhizal Inoculant Investigation – Do They Work?

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Robert Pavlis

Mycorrhizal Inoculant products have been around for more than 10 years but the number of products available is rapidly growing. Clearly manufacturers are finding customers willing to pay for these products, but are they worth the money? Do they work? Are companies able to provide solid evidence that their products work?

I have done an investigation and you will be surprised by the results.

Mycorrhizal Inoculant Products - Do They Work?
Mycorrhizal Inoculant Products – Do They Work?

Mycorrhizal Inoculant Investigation

If you are not familiar with these products have a look at Mycorrhizae Fungi Inoculant Products.

I have studied the science on these quite a bit, but I wanted to know what data the industry has to support the use of their products. Have they done scientific studies to verify the claims they make?

I Googled for “mycorrhizal inoculants” and picked out 5 brands that seemed to be popular, at least in my Google feed. Each of these products is available from numerous resellers in North America and presumably they are purchased by a lot of people. Each one of them have lots of 5-star reviews – for what that is worth.

To be fair to other manufacturers, I will include their products in the blog post, provided someone adds a comment to this post and includes a link to the manufacture’s  scientific supporting research.

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The products I selected are:

Pro-Mix – I do use their soil products but not Connect, their mycorrhizal inoculant.

Myke – a product that has been around for many years.

Dnynomyco – a new product with flashy packaging.

Root Rescue – an Ontario, Canada company with strong horticultural family roots.

Plant Revelation Inc – a new company with attractive packaging.

Claims vs Facts

There is a huge problem with this industry and many other similar industries in the way they misuse scientific facts.

There is clear evidence that mycorrhizal fungi in soil provide a lot of benefits to plants. This is not under dispute. About 80% of plants form mycorrhizal connections.

The problem is that companies claim their product has the same benefits as naturally occurring fungi. To the lay person this seems perfectly logical. If fungi in soil help plants, why would adding more not have the same benefits? WHY? For several important reasons.

Firstly, the commercial products might not be viable – dead spores don’t grow. Secondly, they might not be the right microbes for your plants. Thirdly, and most importantly, the soil is already saturated with fungi. Fungi in soil are at capacity. Adding more does not increase the number of living fungi in soil. This last point is explained fully in this video about compost tea – adding it to soil doesn’t work for the same reason.

YouTube video

In order for manufacturers to make efficacy claims about their products, they need to demonstrate that they actually work in the field (ie not in lab pots). For gardeners this means testing in at least agricultural fields.

Online Evidence of Efficacy

Step one in this investigation was to review each website and check for some scientific evidence that their product works. I consider this a bare minimum for any company who wants to sell this kind of product.

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None of the 5 manufacturers provided evidence on their website that their product works. For a consumer this should be a big read flag for all 5 mycorrhizal inoculants. If I missed such information, let me know in the comments.

Root Rescue did say, An in-depth, five-year study involving over 21 different species of trees showed that those who formed a symbiotic relationship with the Mycorrhizal Fungi were able to adapt and tolerate the stress and challenges of a dry summer season and still thrive. It is not clear if untreated trees also formed such a relationship, but most importantly they did not provide a link to the research study, so the information is not of much value.

A Second Chance to Prove Efficacy

Websites are made by marketing people who may not understand the importance of verifying the worth of a product, so I gave each company another chance.

I contacted them all and asked for the scientific evidence that supports the claims they make about their product.

Pro-Mix got back to me right away and provided so-called “scientific evidence” as seen here. This is an internal study that concludes their product works. It has several glaring flaws.

  1. It was done internally by their researchers – I am sure they are not biased!
  2. It is not published except as an internal marketing piece.
  3. No stats were presented for the data – so you can’t reach any conclusions.
  4. If you look closely, the control soil is completely different than the test soil, so even if we accept the data, it tells us nothing about their inoculant. It only tells us that the two soils are different. Clearly this has not been done by a scientist.

It is a good try, but this is just a marketing piece that does not prove their product works.

Internal marketing piece that shows a test for the Pro-Mix inoculant
Internal marketing piece that shows a test for the Pro-Mix inoculant

Root Rescue also got back to me right away and provided a real scientific research paper that used their product. The website claims that 2,100 trees were tested over 5 years, including 21 species and results show the inoculant “assisted in transplant shock”. The supporting study looked at 6 species between June and Sept of the same year using far fewer trees. The water pressure in the trunks was measured and those growing with inoculant showed higher pressures possibly indicating less drought stress. It is not clear if the drought stress would have occurred in a normal planting with access to water and there is no follow up data to show the long term effects of the inoculant.

Unfortunately the supplied study does not show efficacy of the product.

The other three brands did much worse. They could not even be bothered to respond.

Efficacy of Commercial Products

One study tested 10 commercial mycorrhizal inoculants on a variety of soil-based and soilless potting substrates and found that the “percentage of mycorrhizal colonization obtained with the different mycorrhizal inoculants ranged from 0 to 50%”. This variation was due to both viability of the inoculant as well as the soil itself. “Mycorrhizal colonization did not enhance plant growth”.

Similar results have been found in other studies.

Science on Mycorrhizal Inoculants

There are many studies on mycorrhizal inoculants and for the most part they either don’t work or only work in specific cases. They have been shown to work in both drought and high saline conditions but these are usually not a concern for gardeners. None of the manufacturers of these products provide guidelines for using the product in special situations where they might actually provide a benefit. Instead, they recommend them as a general tonic to be used all of the time and science does not support that kind of use.

YouTube video

The Latest Science About These Fungi

The latest science investigates how tilling affects fungi in soil, and looks at efficacy of commercial products in agriculture. Read all about it in Mycorrhizal Fungi – The Latest Scientific News.

Should Gardeners Use Mycorrhizal Inoculants?

Most well tended gardens don’t have plants stressed by drought or saline so the science does not support their use.

Most gardens have lots of mycorrhizal fungi in their soil and these will inoculate the plants on their own.

Gardeners who use a lot of fertilizer should not bother with inoculants since high levels of nutrients inhibit the plants from initiating a connection with fungi.

I have not seen evidence that these products will be helpful for most gardens. The exception might be very dry gardens that don’t have access to enough water.

Better Ways to Build Soil Health.

10 Easy Soil Testing Methods For Measuring Soil Health

Preventing a Nitrogen Deficiency in Soil – How to Manage Nitrogen Levels

Soil Bacteria – The Myth of Identification & Management

10 Fertilizer Myths That Will Save You Money

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

29 thoughts on “Mycorrhizal Inoculant Investigation – Do They Work?”

  1. Hi!
    I actually don’t find this review to meet my expectations of a good product review. If Robert really wants to know if a product works and can’t find data, he should test it himself to see if his theory is correct before coming to conclusions. If you don’t believe the studies are correct or are poorly done (they often aren’t done well or extensively by manufacturers of any product, there’s implicit bias there), then test the products if you want to give proof they’re useless. You haven’t given any proof that they don’t work, just theories on why they probably don’t. I think there’s a good chance you might be right, Robert, and that many products don’t work, but your reasons for dismissing it are weak. You don’t present much information for readers about soil microbiomes. Saying that soils are already “saturated” with fungi, really isn’t going to impress any serious students of soil biology, who would know that’s while it’s true that pretty much any non sterile medium contains fungi, not all fungi are the same nor do they exist in the same concentration everywhere. Also, it seems to me that manufacturers would be more likely to sell filler material or a fertilizer or useless unhelpful fungi spores rather than dead spores (why bother to grow spores and then kill them before selling them?). I just think that the lack of scientific evidence from a manufacturer proves nothing. In fact, if they did seem to present good research, wouldn’t the implicit bias make it suspect? So one would expect to find most small companies with no “scientific evidence” for their product working. Rather, reviews and satisfied repeat customers would be a much stronger evidence for me that a product worked at some level (even if not for the reasons claimed). I like your review on one level, but I just don’t think it was deep enough.
    Basically you tried to find out if any official scientific reviews of the products had been done, and after not finding them up to the rigorous level you hoped, you felt the products weren’t worth trying. That’s great for you, but only useful to those who believe nothing should be done or tried, till the scientific establishment comes to a consensus and totally vets every product for you. I’m not a commercial fungi producer. Im a gardener, and really the research is in the works for these products. The species of fungi is important, etc, etc. There’s so much science here, and so many companies willing to make a profit at the expense of others’ ignorance. Thanks for being brave enough to post an article like this, but my critique is that you are expecting a high level of science backed research from companies, but then didn’t use much scientific evidence yourself. It was a lot of assumptions. A lot of unknowns and lack of conclusions that led to the conclusion that the products aren’t worth trying. I really wish my comments could be a private critique rather than a public comment, because I think people who do all the work Robert has should be applauded, even if I don’t agree with the solidness of his conclusions.

    • 1) The blog post is not a product review – it was never intended to be a product review.
      2) “If Robert really wants to know if a product works he should test it himself” – clearly you do not understand how science is done. Any testing I would do would be anecdotal data which is meaningless. To test these products a lot of work and time to set up the controls properly.
      3) It is the companies responsibility to get the studies done – before they make claims for it. If the companies making the claims can’t find any science to support their claims, we can be quite sure they don’t exist. Nobody else has a stronger reason to show us the supporting science.

      • Excellent reply! There is no research to back these companies up. Today, there are too many products out there that just do not work. But the government doesn’t stop the companies, and the public keeps buying the latest greatest “snake oil” products without any hard evidence. Soil health management with little to no tillage, cover crops, and manure additions works well; but it takes time. It doesn’t come in a jug or a can! Pivot Bio is a huge one that our university says doesn’t work. Maybe one day the technology can become perfected, but it’s not ready for prime time.

  2. Thank you for your site and sharing. David Johnson has an interesting webinar on Conservation Web with photos showing impressive results from use of his Biologically Enhanced inoculant, made in a Johson-Su Composter (he offers plans and instructions for free).

    It is essentially 1 year old compost, developed with monitored humidity and no turning (air access via tube-shaped 4 inch diameter open slots every 12 in). The product has extensive microbes (lab tested at 3, 6, and 12 months, and shared). I tried to order some of this BEAM inoculant without success (?subcontractor), so am experimenting with crafting some that may be more appropriate for my very different midatlantic climate and soil.

    Are you familiar with this product, or others suggesting multiyear growth improvement from a one time use of very mature compost? If so, I would love to see some links to raw data.

    • I am familiar with the Johson-Su Composter, and have watched some of the videos. I have not seen any data to suggest it is producing special results. But if you have al ink – lets see it.

      • I could not find raw data, but do not have much access to paywalled studies. In the webinar linked above (found from NCRS) Johnson presented the data above, and showed field pictures at 1 year intervals for a few years, after a single inoculation with the aged compost. Growth visibly increased (size) each year for a few years afterwards (not much about baseline soil but did say used regenerative methods). He said the inoculant effect did not spread, or expand further into the next row, and included comparison photos.

        I was impressed, but have not found hard data or confirmatory studies.

  3. Mycorrhizal inoculates are heavily promoted in the cannabis growing industry. Home cannabis growers who grow in pots, in tents, under grow lights are instructed to sprinkle mycorrhizae products in seed holes of the potting soil and around the roots and in the holes of pot soil during up-potting and transplanting of cannabis plants. I’m guessing per this article that, that is a waste of money and does nothing for helping the seed to germinate and grow or for the transplanted cannabis plant to survive and thrive?

    • I am quite sure they don’t affect seed germination, besides cannabis germinates so fast they don’t need help.

      I am sure these growers also add fertilizer with phosphorus – which will stop the plant from forming associations, and then the fungi die.

    • I don’t think that was the thrust of the article. The absence of evidence is not evidence of lack of effect. Sometimes is simply means no one has an interest (typically financial) in asking the question. Further, those who might have an interest (ie those who market the products in question) are often tainted with obvious (and sometimes not so obvious) bias. As an example, a study conducted to show a positive effect may, if the opposite is true actually be suppressed. Sadly, this happens in medical research, too.

  4. Hey Robert,

    Thank you for attempting to help and guide we lay people. I always think of your work when I come across various fertilizer manufactures offering products people generally don’t need. I have recently discovered a line of nutrients from Ventana Plant Science which seems to make incredible claims of a superior manufacturing process/products. But all I see is another company selling the same products…some of which we don’t need, including microbes. Here is a video featuring their chemist.
    Is it feasible that the products they create at Ventana are superior to say Peters/Jacks Nutrients…which I currently use? I realize that there are some risks to discussing specific companies. And I apologize if my question crosses any lines. Either way, thanks again.


  5. Robert, please can you do an article on what you think of the merits or otherwise of Jadam’s natural farming (the need to introduce + increase more local but diverse microorganisms into our soil for its health/plant resilience )?

  6. Hello Robert. Bob Reeves here – I’m the Root Rescue guy, we recently met at the Guelph Organics Conference. I have just read your comments about our product “Root Rescue Transplanter”. As we discussed at the GOC, Root Rescue engaged the University of Guelph to conduct extensive field trials of our mycorrhizal inoculate. Under the guidance of Professor Mike Dixon, the University designed and conducted a multi-year experiment. They decided to look at whether (or not) our product improved the ‘Water Status’ of trees treated (just once) at the time they were planted – and critically – if those benefits persisted over time. As you know, mycorrhizal symbiosis results in several benefits for their host plants – the research team needed to focus on (designed the experiment to discover) whether or not Root Rescue’s inoculate would help newly planted trees gain improved access to soil water.
    This question was chosen for an important reason: if trees (plants) can’t find sufficient soil water in the critical first days and weeks after planting they will fail to survive – this failure to thrive after planting is often referred to as Transplant Shock. The multi-year field trials were conducted with the cooperation of 3 Ontario Nurseries – these nurseries provided not only hundreds of trees, but the land on which the trials would take place. The answer to the question posed by the study was also of great interest to these Industry Partners (the nurseries) because the failure of trees lined-out in their own growing fields is a major financial hit on their business. And also, the nursery industry is under growing regulatory pressure to use less fresh water in their production and growing operations. They need to make less water go farther. And as I personally know after 30 years in the industry, the failure of nursery stock in landscape sites is also a big overhead burden for all landscape suppliers and professionals.
    In the top section of your post, you say that we have not shared the results of the U of G’s research – (we have not made the published article available for download). As you now know that’s not true – in a later section of the post you acknowledge that we do in fact provide a link to the article PDF. As you know not all readers hang in there on a long post, I’d appreciate you going back and correcting the error in the early part of the post. The peer-reviewed article (which was published in the science journal Acta Horticulturae on 06/2015) concludes that our inoculation does indeed (very quickly and permanently) improve the water status of treated trees. This is ‘Proof of Efficacy’ – as concluded by the most respected agricultural/horticultural University in Canada. Here’s a direct link to the page where the PDF can be downloaded:
    Other statements you make are not helpful or are misleading: The post states that Fungi are ‘at capacity’ in soils, so adding more accomplishes nothing. Really, which soils are those? This suggests that ‘Soils’ are all the same in this regard, when in fact a mountain of research concludes the exact opposite. Urban and suburban soils, farm soils (where the crops are grown under a synthetic fertilizer industrialized regime of tillage and monoculture) are often bereft of many of the most critically important soil microbes which support normal, healthy plant growth and productivity. Again, you also imply the ‘Fungi’ are a monolith – all the same, are they? Of all the Fungal types, mycorrhizal fungi (the only ones that form a direct beneficial symbiosis with plant roots) are often in critically low supply in the soils we plant in here in Canada. And (also critically) mycorrhiza are the type of soil fungi most negatively affected by soil disruptions. Saprophytic Fungi might survive disruption (and they perform a valuable service in soils) but mycorrhizal fungi are far less durable – and plants ‘feel’ their absence.
    Our inoculation provides 18 species of dormant mycorrhizal fungi. And here’s the thing – if fungi are (as the post suggests) already there in soil and ready to help newly installed plants – how do you explain the results of the U of G research? The interesting thing to me is that these field trials were conducted on land where professional nurseries have been growing trees for decades – and yet – newly planted trees could not find mycorrhizal partners. Or at least one must logically conclude this – as the only active ingredients in our product are (millions of) dormant mycorrhizal fungal spores.
    And BTW – as stated in the report, all trees (both Treated and Control) in these trials were watered on a regular basis (when rain was insufficient for the survival of the test plants) – dead plants tell no tales. And one more aside, you pose the question “show me research that proves mycorrhizal inoculates are efficacious when plants are NOT under stress”. That’s a very odd question – it implies that plants are typically not under stress after planting – when in fact the evidence is that they almost always are. The successful adaptation of a (nursery-grown, carefully nurtured plant) into any in-ground site (where it must find its way on its own) is highly stressful (read the data in the report). And after growing, selling, and installing millions of landscape plants in my professional life – I can tell you, no matter how much after-care was given to plants that were ‘perfectly healthy when they left the nursery’, too many valuable and beautiful plants fail in unacceptably high numbers (out there in the real world).
    Our inexpensive, safe, and easy to use product is specifically designed (and proven) to reduce transplant shock. If that benefit seems of little value to you, go talk to any landscape professional about the costs of plant failure to their business (and the disappointment from their clients in this regard.) The truth is, soil is often compacted lifeless crap – and applying fertilizers (the very thing that destroyed many of them) does not help. We need to get our heads straight on this – work with Nature – not against her. If our product helps in any way to grow healthy plants and heal the soil, then I’m a happy camper. I never said it was (or is) the be-all or end-all – but it sure made a difference in our own (plant selling and installing) company back in the day – and that’s why I started Root Rescue and brought this organic technology to market.
    Many comments in your post imply that all mycorrhizal inoculates deserve suspicion – “the spores are all dead”. Really – all of us are selling junk? Once again, how do you explain our U of G results? And further to that, let me take exception to one more thing Robert, you say that we are all (once again we’re apparently all a monolith) happy to post positive 4-to-5-star reviews from our customers. To which you say, “for what that’s worth”. I’ll tell you what it’s worth to me – everything. What our clients experience (both home gardeners, growers, contractors, and other landscape professionals) matters more to me than any other form of feedback. And BTW: we post all reviews – good or bad.
    Bob Reeves, founder of Root Rescue Environmental Products.

    • 1) “In the top section of your post, you say that we have not shared the results of the U of G’s research – (we have not made the published article available for download). As you now know that’s not true – in a later section of the post you acknowledge that we do in fact provide a link to the article PDF” – that is not true. What I said was “None of the 5 manufacturers provided evidence on their website that their product works. For a consumer this should be a big read flag for all 5 mycorrhizal inoculants. If I missed such information, let me know in the comments.” This is still true. The link you provided to me is not proof of the claim you make on the site, which is “More than 2100 trees were involved in the 5-years of trials. Half the trees were treated with Root Rescue mixed in water, while the other half (the control group) received only water.

      This in-depth, five-year study involved over 21 different species of trees, and proved the following (with all of the species involved):”

      2) You do have a link to the one study you provided to me on your site – but the link is not with the claims you make, so I never found it. A link to this study is included in the blog post.

      3) The study in #2 does not prove efficacy that the product works. It was a very short term study and did not look at any long term effects. gardeners don’t care if your product increases water pressure in the trunk of the tree.

      4) “he post states that Fungi are ‘at capacity’ in soils, so adding more accomplishes nothing. Really, which soils are those? This suggests that ‘Soils’ are all the same in this regard, when in fact a mountain of research concludes the exact opposite. ” – all soil, but it does not indicate all soil are at the same level. Show me some studies that show some soils are not at capacity? You claim you have a mountain of research?

      5) The study also says, “To assess the response to repeat cycles of drought and recovery of the trees in this field setting, each tree was fitted with an in situ stem psychrometer ” – which indicates the trees were not always watered or else they would not be in drought condition.


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