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 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
- 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.
- 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?
- 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.
- 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?.
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
” fast quantities” Not sure how speedy but did you perhaps mean VAST quantities? What volume did you mean? Is there a way for me to determine what % of beneficial fungi are in my rather poor clay soil? I would be happy not to have to spend extra money for a product I don’t need but want to do the best I can for my spring plantings. Thank you!
Yes it should be vast – thanks.
There is no way for home gardeners to measure this. The way to increase the amount is to build good soil – adding it from a jar will not increase the amount your soil will support. To do this add more organic matter and mulch.
Thank you! More patient continuous work on soil improvement … compost ahoy.
LATELY HAVE ADDED BIOCHAR TO SOIL TO MAKE A NATURAL HOME FOR MYCHORRIZAE AND HELP HOLD MOISTURE
TWICE HAVE HAD GREAT SUCCESS BY ADDING MYCHORRIZAE TO MY GARDEN….ONE BOUGHT AT NURSERY FROM GARLAND TX AND AGAIN BY GOING OUT INTO WOODS AND PACKING LEAVES STICKS ETC FROM UNDER OAK TREES….PUT INTO PLANTING HOLES…..SANDY LOAM….WELL WATER…..GREW BUSHELS AND BUSHELS OF TOMATOES FROM 12 KINDS OF PLANTS…NORTH TX….ROOTS FROM BOUGHT PRODUCT GREW SEVERAL FEET LONG….HAD TO CHOP ROOTS OF PEPPER PLANT OUT OF HALF BARREL THEY WERE SO THICK AND HEAVY……
When you say bare soil, would this include commercial cropland? How does pesticide residue in general affect the microbial life and would a seed coating that included microbes, beneficial fungi and minerals help to recolonize the soil during the cropping season?
Almost all of my comments refer to gardens and not croplands. Every chemical has an effect on microbial life but much of the effect depends on dose. Most pesticide residue is in low amounts and will have limited short term effects, provided that the pesticide is decomposed by microbes. For example, glyphosate is decomposed by bacteria.
There is limited evidence that adding any microbes to soil will recolonize the soil. Existing microbes will tend to out compete the new ones. If the added microbes are native to the soil, but missing, there is a reason for them to be missing. Adding them does not change the environment so they won’t suddenly start to grow. Are there short term benefits – possibly. Could a non-native microbe become established – possibly. There are many variables, and in most cases we can’t even measure the existence of a specific microbe without complex DNA analysis.
Adding nitrogen fixing bacteria with legumes does work, but in this case the seedling provides a home for the microbe.
I want to control Ball moss in my Oak trees with Kocide 3000 or other copper products.
Will Kocide have any deleterious effects on beneficial fungi or other organisms?
Copper will kill most microbes.
I am retired but thinking of starting a lawn service. Your site is very informative on just what I need to know on grass and gardening. Knowledge is power to this new transition.
I love your posts–I’ve been searching for a website that will provide some useful information rather than repeating the same generic “established” information.
Why is it that there are so many people on YouTube that claim the effects of purchased mycorrhizal fungi is so awesome and they will show tests that seem to prove it works??
Some are promoting their own products. Many others believe any marketing they see.
I’ll bet that not one YouTube video uses proper controls and replicates to show that mycorrhizal fungi work. If you find a good one, post the link here and I will gladly review it.
I accidentally came across a company called groasis with a series of videos experiments on YouTube. Their main product to sell is some kind of pot that allows you to water less, which they are testing in the videos, but they also are testing mycorrhizae additions to replace fertiliser. In this case they have a vast number of plants, with mycorrhizae additions and controls, and clearly show the benefits in the plants growth that had mycorrhizae added. They have no mycorrhizae product to sell and do not even report on what product they used. From this I can imagine the benefits of adding mycorrhizae specifically when starting seeds in pots when using commercially bought potting compost, as there is probably little chance that this has much in the way of mycorrhizal activity, and could give the pants a good start. However, I will do my own experiments, including trying to make my own mycorrhizal additions naturally, which is actually what this groasis company recommends. You can find their videos on YouTube if you are interested to see their results (and controls).
It can have benefits in pots that are not fertilized. But it is much easier to fertilize, which most people do. With fertilizer, plants don’t form associations with mycorrhizal fungi. Excess phosphorus actually kills them.
I added a mycorrhizal innocculant called Mykos from Xtreme Gardening to the surface roots of avocado trees. I later saw white fuzziness around the tree roots near the surface. Then, I saw mushrooms of different types spring up after rains. I have seen similar fuzzy white growth in the pine bark mulch on untreated avocado trees. I don’t know if the innoculation may have introduced new types of mycorrirhizae. But they appeared to survive and add diversity to the mushrooms, several of which were quite weird looking (horn-shaped) and strange, dying quickly but attracting flies before they died.
I am convinced that I introduced new species but not that these were more beneficial than native species, although they clearly survived and flourished to reproduction (indicating that the product was viable). Those flies may have carried them to the yards of neighbors? Given the large number of species, adding diversity may be helpful? I enjoyed the experiment in any case.
I enjoy your articles, Robert, and every one aligns with my gardening experience.
By the way, and I should have posted on a different article, a product called Sluggo, does kill all snails and slugs, and stays active, partly due to snail and slug cannibalism, I think. Snails are an introduced species here in California so my remorse is non-existent.
Some scientists are concerned that we might be spreading invasive fungi species. What harm might they do long term? Nobody knows.
Info very informative
What about in a baren Mojave desert with clay soil? How do you ammend that? Where I live the temperatures can get up to 120°f. That makes the soil hotter as the nitrogen escspes at a very high rate. Ive been experimenting with the deep bed method as promoted by John Semour, but I am still unsure of ratios of matter to put in the soil. Some say Gypsom, others sand, some say black soil and top dressing of compost as too much in soil or in pots would heat up the plants. Would mycorrhizal fungai be a waste here? My husband and I are elderly and are trying to grow our own food for health and cutting expenses.
If mycorrhizae fungi could live in your soil, it would already be there. That is one of the misunderstandings of this product. The fungi only live where conditions are suitable for them. And if conditions are suitable for them, they would already be there.
If you think it might help, next time you go visit someone with a garden, bring back a couple of scoops of soil – that will work better than the commercial product.
Thank you.
Add some manure and sphagnum Moss. Those things help retain or drain water as needed so your plant isn’t too thirsty or too moist.
It is a good idea to add both of these but i think both retain water.
Add them as mulch and don’t dig them in.
I believe the answer ,at least in part, to the question to high temperature area soil is found in the natural design of falling organic matter. This idea of leaves and other loose matter provides for solar shielding, remote shade perfectly placed above soil as heat rises thus not raising soil temps, indirect airflow for oxygenation, rain or water flow, and orgainic matter to feed the microbial life in the soil.