Mycorrhizal Fungi (mycorrhiza) Myth

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Robert Pavlis

There is no doubt that mycorrhizae fungi play an important role in plant growth. They help aggregate the soil which in turn provides plant roots with better access to water and oxygen. Their symbiotic relationship with plants helps them access water and nutrients. It is only natural that companies want to sell these fungi to you. Don’t fall for it.

mycorrhizae mycelium attached to larger plant roots
Mycorrhizae fungi (white hairs are the mycorrhizal fungi), source: Microbe World

Mycorrhizae Fungi

Mycorrhizal fungi (mycorrhiza) are found in all soil where plants grow. They form large networks of fine filamentous growth throughout the soil. They associate with plant roots; some even burrow into the roots to create an even greater association with plants. About 80% of all plant species form some type of association with these fungi.

Think of mycorrhizal fungi as a vast network of very fine plant roots. They are not plant roots, but they behave in similar ways to plant roots. They burrow into nooks and crannies in the soil and collect water and nutrients for the plants. In return the leaves of plants send sugars to the fungi as food. Given this important association it is natural for one to think that it would be beneficial to add more mycorrhizal fungi to the soil. For a more detailed description of mycorrhizal fungi see Microbe Science for Gardeners.

Arbuscular Mycorrhizal Fungi

There are two basic types: EM and AM.

EM fungi (ectomycorrhiza) form associations with only about 2% of plants, mostly the woody plants like trees and shrubs. Since woody plants make up a large portion of the plant community, they are important to natural ecosystems but they are not usually found in commercial products for the garden.

AM fungi, called arbuscular mycorrhizae (a type of endomycorrhiza), make up the largest group and form bonds with the majority of plants. They provide mostly phosphorus to the plant. These are obligate symbiotic fungi, which means they can not survive for long without a host, although they can produce spores (a types of seed) that can survive until a host root shows up. This is the type found in commercial products.

The fact that they can survive as spores is important because it makes it easier to produce them. Commercial products contain a combination of spores, small fragments of mycelium and small pieces of roots that contain bits of fungi. Together these are called arbuscular fungi propagules and the number is listed on some commercial packaging. For example one product claims to have “60,000 propagules per lb”.

Facts About Mycorrhizae

  1. Garden soil already contains vast quantities of mycorrhizae, or at least it does if any kind of plants grow in it. Adding more is a waste of money, since they are already in your soil.
  2. Manufactured mycorrhizae consists of 2 or 3 types of fungi. It turns out that there are hundreds if not thousands of different kinds in your soil and some of these are very specific to certain types of plants. How do you know your plants will benefit from the 2 or 3 types you buy?
  3. Manufactured mycorrhizae are heat sensitive. If the container is left in a greenhouse, or a transport truck too long, the heat kills the fungi. There is no way for you to know that the product you buy contains active fungi – they could all be dead.
  4. Manufactured mycorrhizae are of a specific species, almost certainly from an area that is foreign to your soil. It is possible that these foreign species inhibit the growth of your native species. You have no way of knowing but it is never a good idea to import foreign species of any kind into your garden.

There is just no good reason to buy mycorrhizal fungi for your garden.

Special cases

There are some special cases that might warrant the addition of mycorrhizal fungi.

Bare Soil:

Soil that has no plant growth probably has few natural fungi. It would seem that this would be a good case for adding them. The problem is that if the soil is not suitable for plant growth, it is probably not suitable for the growth of mycorrhizae. Adding them will simply result in them dying. If you want to grow plants in this soil you first need to solve the problem in the soil. As plants start to grow, native mycorrhizal fungi will also show up, naturally.

Sterile potting soil:

Sterile potting soil used in containers has no natural fungi. Studies have shown that adding mycorrhizal fungi to this type of environment can have some positive results. Keep in mind that the main value of the fungi is to provide the plants with water and nutrients. In a potted situation, many gardeners over water and over fertilize, negating the benefit of the fungi. If you water and feed your plants regularly, there is little benefit to adding mycorrhizal fungi.

Commercial Inoculants vs Compost

Most commercial products have a dozen or fewer species in the product. Some don’t even list the species. A recent analysis of a compost sample showed that it contains 305 fungal species and 360 bacterial specials.

In a recent review I checked with 5 commercial product manufacturer and asked them for proof that their product worked. You can read about the results in Mycorrhizal Inoculant Investigation – Do They Work?.

Soil Science for Gardeners book by Robert Pavlis

The Latest Science About These Fungi

The latest news investigates how tilling affects fungi in soil, and how effective commercial products have been in agriculture. Read all about it in Mycorrhizal Fungi – The Latest Scientific News.

The latest data clearly shows that claims such as “In soil that has recently been tilled/worked, mycorrhizae will be lacking” are not true.

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!

158 thoughts on “Mycorrhizal Fungi (mycorrhiza) Myth”

  1. How well do mycorrhizae perform in container gardening? Container gardening relies on large pore potting soils for drainage and aeration, which seems to be an unlikely environment for mycorrhizae and other microbes to flourish. Waterlogged soil is also a problem in containers, forming an anoxic zone (dead zone). Would mycorrhizae and other microbes be asphyxiated in waterlogged soils?

  2. Endo mycorrihizal fungi will only grow within live roots. Ground left fallow will not contain any.
    Endo do not sent sporer into the air.

  3. Glad I ran across your article while doing research on adding fungi inoculant to our soil. My gut feeling was that our soil already had native types of fungi and that our homemade compost had all the healthy fungi inoculation our soil would ever need. But wanted to check on it with other sources.
    We decided to use our home brewed inoculant made through compost along with cover cropping, green manure, using no-till methods, and biodiversity. We like the philosophy of building healthy soil through regenerative and permaculture practices.

    • 1) this is an older post but the contents are still valid. The conclusion is that “There are some special cases that might warrant the addition of mycorrhizal fungi but there is just no good reason to buy mycorrhizal fungi for your garden.” – that conclusion is still valid. none of your references even discuss the use of mycorrhizal fungi in gardens.

      2) A recent review of several commercial products found that6 none of them had scientific data to support their use. Discussed here and post for this has been started.

      3) Your first link. Will have a closer look. If valid it shows benefits of using the products on soybean. There are examples in agriculture where specific inoculants are beneficial in specific cases – usually drought or saline conditions. That does not support the idea of general use in a garden.

      4) Your second link. Here is the whole article “AMF samples were trap-cultured for 6 mon using red pepper (Capsicum annuum) as a host species.” – these were clearly not commercial products.

      5) Your third link reviews commercial products but does not try to evaluate their efficacy. It also says “Most of these products are mainly applied to cereals; however, AMF inoculation faces the challenge of having short product shelf life”. It does not comment on the use of these products in gardens.

    • I have had a look at your first reference. The results do show positive results with mycorrhizal fungi, but it should be noted that the testing was done is very sandy (88%) soil. No information is provided about watering the fields in this condition.

      That is important. Numerous studies have shown added mycorrhizal fungi help plants grow in drought conditions and since this work was done in sandy soil, it is possible that such conditions existed. When other studies were done in non-drought stressed conditions, results were not positive.

      The commercial product is Rootgrow and the manufacturer provides zero information about the microbes in the product.

    • I bought xtreme mykos and little did I know there was an expiration date ON THE CUT OFF PART OF THE BAG! and all my plants died what I used it on??? the company is giving me the run around also! I got from Amazon and they said they could not help me? I cannot find anything ANYWHERE that talks about this?>>??

      • I doubt it would kill your plants unless the product had something toxic added to it. A normal product will not harm plants.

  4. What about fungal and bacterial inoculants for hydroponics, where there is no soil or organics?

    I know sterility in hydroponics is a myth (not possible), so some microbes will naturally develop. But are these the strains we want in the nutrient solution?

    Which leads me into another question — is there anything to the idea that populating soil, or nutrient solution, with the “best” strains will sort of push/crowd out other microbes, and develop a better microbial environment, especially in hydroponics?

  5. I feel you are close-minded to the fact that people are bringing up situations where the network was destroyed by man in some way. In a situation where the network is destroyed by tilling or some other action an Inoculation of new or more fungi can be beneficial for restarting the population. I said can be not is beneficial. Farmers and gardeners are scientists in a way. They farm the same land every year. They get a feel for it and when they introduce something and they notice a difference from that point on, I’d say that can be scientific. Soilless media like coco and bark should benefit from the inoculation of fungi and bacteria. I wrote this quickly and didn’t look for anything to link. There are a lot of studies happening at the moment with a lot of different plants and the benefits of adding bacteria and fungi. Dr. Bruce Bugbee at Utah State University is very knowledgeable and is a professor of horticulture there. He has found the benefits of adding many different things to what we grow, especially to indoor gardens!! I would love to take his class! You ask for links and have been asked repeatedly to show yours and you haven’t. Why don’t you let people make up their own minds? If they use it and see better results then they should continue to use it.

    • ” the network is destroyed by tilling or some other action an Inoculation of new or more fungi can be beneficial”

      1) where is your proof that this is true?
      2) tilling may damage fungi growth – it does not “destroy” all the fungi.

      “Farmers and gardeners are scientists in a way” – no they are not. All you have to read comments on line from gardeners – virtually none use controls and reps the way a scientist would

  6. I live in a small remote island in Indonesia where it was hit by tsunami in 2010. Since lockdown, I’m determined to grow my own food to minimize the cost of food shipping. Being new (and excited), I was looking to buy a lot of stuff to make sure my soil is fertile and whatnot. (Currently it’s pretty sandy and rocky, but there’s swampy area where it has decent amount of black soil when it’s not flooded). I’m lucky I find your site before i spent any money to buy stuff I don’t need. I’ve seen the proof myself for this article. I moved a bag of soil from the dried swamp to my garden bed, planted Basil, and left it alone for quite a while. Never added anything. Later on I found it was full of root like structure which I think are mycorrhizae. I really appreciate you taking the time to write your knowledge in this site, I’ve been reading a lot of it. (Sometimes the comments of some people are pretty entertaining too 😉

  7. You said Manufactured mycorrhizae consists of 2 or 3 types of fungi. It turns out that there are hundreds if not thousands of different kinds in your soil and some of these are very specific to certain types of plants. How do you know your plants will benefit from the 2 or 3 types you buy? and then go on to say “ Studies have shown that adding mycorrhizal fungi to this type of environment can have some positive results.” seems like a contradiction

    • The second quote refers to sterile soil. It also says “some positive results” – it does not say positive results with all plants.

      • There are only three species of native mycorrihizal fungi in the soil I plan to plant in – Tuber, Scleroderma and Rhizopogon rubescens.

        My question is: Do you think introducing three new species of mycorrhiza fungi (Claroideoglomus lamellosu, Funneliformis mosseae and Scutellospora calospora) would be beneficial for my plants?

        • Probably not. Do your plants need these three species? Would they survive in competition with the existing three species? If they would survive, why are they not already there?

  8. I was disappointed after reading your message about adding Micro fungi. I just spent ten bucks on 2oz. of it. I guess since I already have it I’m going to do my own tests.


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