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?

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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.

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.

Growing Great Tomaotes, by Robert Pavlis

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.

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.

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.

It was done internally by their researchers – I am sure they are not biased!
It is not published except as an internal marketing piece.
No stats were presented for the data – so you can’t reach any conclusions.
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

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”.

Plant Science for Gardeners by Robert Pavlis

Dr. Cobbs, who has done presentations for the Soil Food Wed School, tested commercial fungal products and found, “no evidence of benefit; commercial inoculants never increased native plant biomass, although several inoculants decreased the growth of native species and increased the growth of invasive plant species.”

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.

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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