Mycorrhizal Fungus

If I had to pick what is the most important thing to do for your plants to ensure their health and vigor (other than basic needs, like sunlight, water, etc.), it would be really hard to choose between compost and mycorrhizal fungus. In the end, though, I would probably choose mycorrhizal fungus, just because there are more plants that are adapted to rocky, nutrient poor soils than there are plants adapted to life without mycorrhizal fungus.

Mushroom-producing fungus (hereinafter abbreviated to "mushrooms") fall primarily into three categories: parasitic, saprophytic, and mycorrhizal. Parasitic mushrooms harm and/or kill other living organisms. Saprophytic mushrooms break down organic matter that is already dead. Mycorrhizal mushrooms are a bit more complicated to define and are the subject of this post.

The discovery of mycorrhizal mushrooms, exactly what they do and how amazingly important they are is a relatively recent one. Scientists have discovered that the root system of plants doesn't really do what we thought it does, at least for most plants. It turns out that roots aren't all that good at collecting water and nutrients from the soil. The roots' main purpose is to connect up to networks of fungus that live in the soil nearly everywhere called mycorrhizae. The plant then forms a symbiotic relationship with the fungus. The plant provides sugars to the fungus through its root system, in some cases sending as much as 80% of the sugar the plant produces. The fungus, in turn, does what it does best. It sends filaments far and wide to search out the nutrients that the plant needs, break them down, and deliver them right to the roots of the plant. Think of it like a living fertilizer, getting the most out of the soil. It also seeks out and concentrates water, delivering that to the plant as well, increasing the drought tolerance of plants. It turns out that approximately 90% of all plants on earth, including all or nearly all of our cultivated, food-producing plants, are evolved to take advantage of this relationship. Plants that have the appropriate mycorrhizal mushrooms in the soil with them will be healthier, grow faster, resist pests and diseases better, be more drought tolerant and have a much better chance of surviving stressful conditions.

My first attempt to use mycorrhizal fungus was a dramatic one. I have a tree aloe in a pot. When I got it, it was about 4 inches tall. Over the next 4 or so years, it grew to be about 8 inches tall. I finally decided it needed to be repotted. About this time, I bought my first treatment of mycorrhizal mushrooms. When I repotted the tree aloe, I inoculated them with the mycorrhizal mushrooms. Normally when you repot a plant, it sits there for about two weeks in transplant shock while it repairs its root system and adjusts to its new environment. My tree aloe showed obvious new growth the next day. Over the next 6 months it grew from 8" high to nearly 2' high.

The most dramatic example I have heard of regarding what these amazing mushrooms can do was from an experiment performed by mycologist Paul Stamets. He went out in the woods in the Pacific Northwest and found two trees growing side-by-side, one a deciduous tree, the other a conifer. They were able to confirm that the same individual mycorrhizal fungus was growing on the roots of the two trees, connecting them. They then tented both trees. One tree got a clear tent and a supply of carbon dioxide with a special, traceable isotope of carbon. The other tree was tented with black plastic to block all access to light. They allowed time to pass and then tested the tissues of the stressed tree. The tissues of the tree showed significant quantities of the carbon isotope they had provided to the other tree. The only way that is possible is if the mycorrhizal fungus in the soil had been accepting the sugars from the healthy tree and providing them to the stressed tree in an attempt to nurse it back to health.

Mycorrhizal fungus are present in the soil in nearly every natural environment in the world. However, human activities of moving and compacting soil from activities such as plowing and construction destroy native populations of mycorrhizal mushrooms. Fortunately, you can buy supplements to restore populations of mycorrhizal fungus. One such source is the website of the mycologist mentioned above, www.fungi.com. There, he sells a product called Mycogrow(TM), that restores the mycorrhizal mushrooms to the soil.

It is also worth mentioning that while some of our best culinary mushrooms, such as truffles and chanterelles, are mycorrhizal mushrooms, these have proven very hard to cultivate as they are evolved to pair with a particular tree in a particular ecosystem. The mycorrhizal mushrooms that you can buy spores for will produce mushrooms, but only tiny, inedible ones. They are more for helping the plants than for producing edible mushrooms.