What is Mycorrhizae and How Does it Benefit Plants?

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Introduction

As a gardener, you may have heard the term Mycorrhizae. You may have even purchased some of this stuff for your garden or seed starting.

But what exactly is this Mycorrhizae and why is it so good for your garden? Well, I hope to help answer that in this article without getting too detailed in the science.

Mycorrhizae is a classification of fungi, the types of fungi that have a symbiotic (mutually beneficial) relationship with certain plant roots. Unlike various bad fungi, Mycorrhizae are usually beneficial to the host plant. I say “usually” because that is not always the case. I will try to explain that further in this article.

Mycorrhizal Fungi live on around 85 to 95 percent of the plants we currently know today. That is a lot considering there are around 400,000 species of plants. It is supposedly in most soils already.

A Few Terms to Know

Before we get started, I feel that it would be a good idea to start off with a few terms. The first three here tend to be used interchangeably and are often used incorrectly, as I do myself and most likely do in this article.

Mycorrhizal is to describe the fungus or fungi. It is an adjective and is strictly about the fungi, not the roots or the relationship between the roots or fungi.

Mycorrhiza means “fungus-root”. This is the singular noun describing the relationship between the root and the fungi.

Mycorrhizae, which are the fungi that has a mutual relationship with the roots of many different plants. This is the plural version of mycorrhiza.

Propagule, the plural is propagulas. This is the bud, sucker, or spore…the detachable portion of the plant that can grow another plant. For mycorrhizae, this would be the spores of the fungi. Most brands you buy give you the number of propagules per gram for the type of mycorrhizae they are providing you in the package they are selling.

Hypha (Hyphae is plural) is the long branching thread like filament of the fungi. This is the main system in fungi responsible for absorbing nutrients from the surrounding soils and transferring them to the host plant. In many fungi, hyphae form very intricate networks that allow the organism to spread out and colonize in new areas, similar to how plant roots spread.

Types of Mycorrhizae Fungi

There are two general categories of Mycorrhizae Fungi…endomycorrhizae and ectomycorrhizae.

Endomycorrhizae

This type of fungi produces hyphae on the inside of the plant roots.

Arbuscular Mycorrhizal Fungi (AMF)

This is the most common fungi species of Endomycorrhizae, occupying approximately 80% of all plant species. Arbuscular Mycorrhizal Fungi penetrates the cell walls of the plant roots and creates a branching structure called arbuscules.

Ericaceous Mycorrhizae Fungi (ERM)

Also a type of Endomycorrhizae and it does penetrate the root cell walls, but without creating arbuscules in the root. As the name implies, they are associated with the plant family Ericales.

Orchidaceous Mycorrhizae Fungi (OMF)

Also a type of Endomycorrhizae and it does penetrate the root cell walls. As the name implies, they are associated with the plant family Orchidaceae (Orchids).

Ectomycorrhizae Fungi (EMF)

These fungi form a sheath around the roots of trees and shrubs, but do not penetrate the cells of the plant roots. Instead, they create a network of hyphae that extend into the surrounding soil to absorb the nutrients in the surrounding soil. These fungi associate mostly with conifers and some deciduous hardwood trees.

What’s in the Package?

When you buy mycorrhizae, you will find different types being sold. Below is a list I put together showing what different brands provide in their product (I used Amazon to get the following information).

Brand #1 had:

• Rhizophagus Irregularis – This is Endomycorrhizae

Brand #2 had the following:

• Glomus intraradices – This is Endomycorrhizae
• Glomus mosseae – This is Endomycorrhizae

Brand #3 advertises they contain arbuscular mycorrhizal fungi types:

• Rhizoglomus irregulare
• Funneliformis mosseae
• Funneliformis caledonium

Brand #4 contains 5 endomycorrhizal species:

• Rhizophagus irregularis
• Rhizophagus aggregatus
• Rhizophagus proliferum
• Rhizophagus clarus
• Claroideoglomus etunicatum

Brand #5 contains 1 endomycorrhizae:

• Glomus intraradices

Brand #6 contains many species:

• 4 Species of Endomycorrhizae
  • Glomus Intraradices
  • Glomus Mosseae
  • Glomus Aggregatum
  • Glomus Etunicatum
• 7 Species of Ectomycorrhizae
  • Rhizopogon Villosulus
  • Rhizopogon Luteolus
  • Rhizopogon Amylopogon
  • Rhizopogon Fulvigleba
  • Pisolithus Tinctorius
  • Scleroderma Cepa
  • Scleroderma Citrinum
• 4 Species Rhizobacteria
  • Bacillus lincheniformis
  • Bacillus pumilis
  • Bacillus subtilis
  • Bacillus megaterium
• 3 Species Beneficial Fungi
  • Trichoderma harzianum
  • Trichoderma viride
  • Trichoderma longibrachiatum

Wow! That was a long list for Brand #6 but it isn’t the longest list I have seen. Joy went to Lowes today (at the time I was writing this) and found a small package of Mycorrhizae for a few dollars. Because I am writing this this article, she picked up one of those packages for me. When I was looking at what is in that little package, I was amazed at how many different varieties of mycorrhizae it contained along with the numbers of bacteria.

Note:
You may see Rhizophagus irregularis or Rhizophagus intraradices, this was formally known as Glomus intraradices until the reclassification of this arbuscular fungus took place around 2001. Some package labels still identify Glomus intraradices as shown above and if you research older material, you will find the older term as well since those older materials may never get updated.

Alright, this is a pretty extensive list and you may be wondering why I went through this effort to confuse or bore you…

There are many species of fungi and as shown above, you will see many different names that will probably mean nothing to you. I mean really, who in the general population will really know what any of these species of fungi are and what they do? The most important thing to take from this is the type, typically endo- or ecto-, as that is the most critical piece of information for most plants due to their association with the fungi. Keep reading to find out what type to look for based on the plant type.

Does the quantity of different species in a product matter? According to Jeff Lowenfels (the author of Teaming With Fungi), quantity does matter as the more variety you have in propagules increases your chance of getting the fungi and host plant to match up correctly (Different species of fungi associate better with different host plants). Others on the internet say that it doesn’t matter and one will be fine. I have found that most of the searching online I have done to get an answer to this comes from manufacturers/suppliers of mycorrhizal fungi, which could be questionable since they are selling a product. Since Jeff does not sell mycorrhizal fungi and appears to be very knowledgeable with nearly all microbes under the soil, I personally would trust what he says…the more the merrier.

How Mycorrhizae help plants

There are various ways mycorrhizal fungi helps plants and the soil they are in. Here are some of those benefits:

• Nutrient absorption: mycorrhizae increase the surface area of plant roots for better nutrient uptake. They also extend the reach in the soils with hyphae as described above.
• Drought resistance: helps plants tolerate drought stress by bringing in additional moisture into the roots
• Disease resistance: can protect plants against soil-borne diseases
• Soil improvement: can improve soil structure and fertility

Benefits to the Fungi

We cannot leave out the benefits to the fungi, especially since this is supposed to be a “mutually beneficial relationship” between the plant and the fungi.

In a nut shell, the plant provides food and nutrients created by photosynthesis and feeds some of that to the fungi. This allows the fungi to continue growing and reproduce.

Mycorrihizae does not help all plants

Certain plants have no association with mycorrhizal fungi at all. These includes plants from the Brassica Family and Ericaceae Family.

A couple other plants I have come across include beets, buckwheat, rapeseed, and radish. Radish!? That one surprised me for some reason, probably because they are a nice small plant and we sometimes grow them where we have room and because they are a very common and easy plant to grow. Some of these plants release a chemical when they decompose which may prevent the mycorrhizal fungi from forming. Even worse, this chemical apparently can stay in the soil even after the plant has been removed from the garden bed. How long does this chemical stay in the soil? I have not found the answer to that yet and I would suspect that it would depend on a few factors such as soil type, watering habits, and type of garden bed.

With this information, it seems important to keep these types of plants out of the planter beds where you want to grow mycorrhizal fungi.

What Type of Mycorrhizal Fungi Should you be Applying?

Okay, so this may have been a bit of a confusing and complicated topic. Nothing seems easy anymore. One of the questions I had myself was “what kind of mycorrhizal fungi should I be looking for in the packages for different plants?”

Fungi Perfecti put together a pretty comprehensive list of various plants and their association to Engo- and Ecto- compatibility. You can check out their list here.

That list should hopefully help you out. Look for the type of plant you want to apply the mycorrhizal fungi to and it will tell you what you should look for.

How to Apply Mycorrhizal Fungi to your Plants

Because this is a root fungus, the mycorrhizae needs to be applied to the roots for it to give the best results.

You can do this a few different ways:

1. Inoculate the seeds prior to planting the seed. This will give the fungi direct contact to the root when they begin to form.
2. If transplanting, you can apply the fungi to the roots directly while transplanting.

Because mycorrhizal fungi may come in different forms (powder, granular, and even liquid form) follow the directions provided by the supplier.

The Importance of Soil Testing

Check the levels of nitrogen and phosphorus in the soil by doing a soil test. Too high of a level of either of these will prevent the host plant from creating or working with mycorrhizae. It doesn’t kill the mycorrhizae, it just prevents the host plants from associating with it.

A soil test showing the level of phosphorus should be performed prior to inoculating the soil or roots with mycorrhizae fungi. If the level is high, the application of mycorrhizae may be ineffective since the high levels of phosphorus may reduce the chances of the mycorrhizae from colonizing on the roots.

Different plants have different needs when it comes to nutrients, including phosphorus, and it can vary depending on the type of soil, the amount of fertilizer used. Phosphorus levels may also be impacted by the level of PH in the soil.

How to Care for the Mycorrhizal Fungi

There are a few things you should or shouldn’t do if you want to build up the network of mycorrhizae in your soils.

1. Do not apply fungicides as this may kill mycorrhizal fungi (It’s a fungus).
2. Avoid synthetic fertilizers and pesticides.
3. Follow the manufactures instructions for storage.
4. Try to reduce the about of soil disturbance to avoid breaking the network of hyphae. This means to avoid tilling the soil.
5. Soil test. Avoid high levels of nitrogen and phosphorus.
6. Avoid soil compaction. Compacted soils can limit the ability of mycorrhizal fungi to penetrate the soil and form associations with the plant roots.
7. Maintain the soil moisture so the fungi don’t dry up.

Do you need to apply mycorrhizal fungi to your soil?

Alright, this is the next big question. This stuff is somewhat pricey so do you really need to apply mycorrhizal fungi to your soil? Maybe, maybe not.

Keep in mind that your soil may already contain mycorrhizal fungi, in which case your plants may already being doing fine. If they are doing so great, there are a few signs that may indicate the need to apply this fungi, either because it is lacking the fungi or that it may not be thriving as it should.

If you have been fertilizing your plants and they are not growing as they probably should or as you expect them to, or if they are showing signs of nutrient deficiencies, this could be a sign that the fungi are not functioning properly or are not in sufficient quantities. Try following the items listed above in “How to Care for the Mycorrhizal Fungi“.

Recommended Reading

An absolute wonderful book to read if you really want to dive into the world of fungi for gardening, I highly recommend “Teaming with Fungi – The Organic Grower’s Guide to Mycorrhizae” by Jeff Lowenfels (Paid Link). This book is loaded with information on mycorrhizae and it can be a bit overwhelming on the first read, but going back a second time to research certain terms or species and other information, I have found that it all started to come together much easier.

If you enjoy that book, I also recommend his other books, in order of publication:

• Teaming with Microbes (Paid Link)
• Teaming with Nutrients (Paid Link)
• Teaming with Bacteria (Paid Link)

I am currently reading Teaming with Bacteria and have enjoyed it so far, just like the other three books. Each book is specific to the title, but you will learn how each are related to each other when it comes to soil and plant health.

Conclusion

Mycorrhizal Fungi has been around since the beginning of living plant matter. It is in nearly every soil naturally. However, due to a lot of factors such as soil disturbances (tilling, grading, etc.), addition of synthetic fertilizers and pesticides, soil compaction, drought, and so on, we need to help replenish mycorrhizal fungi in our gardens.

There are quite a few benefits this fungi has on the plants, inside and outside your garden. Let’s take care of them so they can take care of us by helping our plants thrive without the extra chemicals. With the proper care, this fungi and all the other beneficial soil microbes will do their part. There are a lot of forests out there that continue to grow and thrive without our assistance with synthetic fertilizers and our gardens can do the same if they are handled properly.

Rick Simper has various hobbies, including woodworking, metalworking, composting, and gardening. He is an Architect full time and uses these hobbies to get away from the busy week of Architecture.