Mycorrhizal fungi and inoculants - Garden Myths

Mycorrhizae Fungi 

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.

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, have a look at this publication by Dr. Linda Chalker-Scott.

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.

A soil without microbes is not complete, and can not become a self-sustaining ecosystem. With a

symbiotic relationship that dates back 450 million years, mycorrhizal associations have evolved into a critical component of successful restoration projects across several continents.

• Mycorrhizal fungi make up over 90% of the living microbial biomass that is present in most soils.
• Mycorrhizal fungi make up over 90% of the living microbial biomass that is present in most soils. The picture provided details mycorrhizal hyphae connecting the fine root hairs to vast regions of the soil, where the hyphae transport carbohydrates to other beneficial microbes, particularly plant growth promoting Rhizobacteria (PGPR). The mycorrhiza fungus obtains the carbohydrates that it requires from the roots, and in return provides plant nutrients including nitrogen and moisture through the hyphal network.
• Mycorrhizal inoculant extend the grass roots deeper, improve the soil structure, and join plants together for easier maintenance and less watering. Healthy soil and soil biology can eventually eliminate weeds. Plants colonized with mycorrhizal fungi produce significantly larger root mass and are therefore more capable of handling stress from drought, pathogen attacks, and other forms of environmental stress. Mycorrhizal plants have access to more volume, and therefore more moisture compared to plants that are not colonized by mycorrhizal fungi.