I hear a lot of claims out there regarding mycorrhizal fungi. This article is an attempt to help growers weed through the misinformation and marketing hype to decide what product is best for their garden. It is based on the research I've done on the subject over the past 8 years, but I am always learning new things and will update the article accordingly.
What Is Mycorrhizal Fungi?
So what is mycorrhizal fungi? It's a fungus that forms a symbiotic relationship with the roots of most plants. In a natural system, it is one of the primary ways the plant receives phosphorus, but it has many other benefits as well. For fruit trees, veggies, and cannabis, we want endo-mycorrhiza. The most widely researched species being Glomus mosseae and glomus intraradices. Just to make things more confusing, glomus intraradices can also be listed at g. intraradices, rhizophagus intraradices, or rhizophagus irregularis depending on how current the manufacturer is with terminology. Here's a quick list of what to look for when using mycorrhiza:
What to Look for Before You Buy Mycorrhizal Fungi
- High phosphorus also inhibits mycorrhizal infection. Makes sense, right? Studies have found that if high phosphorus was applied at the same time as the mycorrhiza that the plant didn't bother making that association since it already was getting what it needed directly from the soil.
- It needs to be applied directly to the roots. Don't water it in over the top or mix it throughout your soil.
- It's a 1x application at the beginning of your plant's life cycle.
- Reusing soil means having spores and hyphal fragments already in the soil and repeat applications may not be needed depending on how the soil has been managed.
- Don't add it to teas. This relates back to the fact it's a root symbiont. It needs to come in direct contact with root exudates in order to grow. In a tea, it's not doing anything and may become an expensive food source for other microbes in the tea.
- I hear people online mistake mycelium for mycorrhiza. Keep in mind they are different. Mycelium is visible with the naked eye, while endomycorrhiza is not. You need a microscope and stains to effectively see endomycorrhizal infection.
- Endomycorrhizal fungi do not produce fruiting bodies (mushrooms). If you see a mushroom it has no relevance to whether or not your plant has a good mycorrhizal infection.
- LOOK AT THE SPORE COUNTS LISTED ON THE PACKAGE! I can't emphasize this enough. Many products have a low spore count and are still very expensive. Or products will have high spore counts but it's because they've added ectomycorrhizal fungi or other microbial products. For simplicity purposes, only look at g. intraradices or g. mossae (NOTE: it may also be listed as rhizophagus intraradices or rhizophagus irregularis instead of glomus intraradices).
- Reading the package isn't enough. Recent testing from the Oregon Department of Agriculture has shown that not all microbial products contain the levels of microorganisms guaranteed on the label. To see the list of the products they tested and the results, you can click on this link.
- Not all strains are the same, so even if 2 products from different companies say g. intraradices, you should be aware that they may perform differently. Best to test out what strain does best in your environment.
If you wish to do more research and reading on mycorrhizal fungi pick up Jeff Lowenfels' book, Teaming with Fungi. I also did an interview with Dr. Yoram Kapulnik, an expert on the subject. (Episode 77)
Where to Buy Mycorrhizal Fungi
If you would like to try mycorrhizal fungi out in your garden, I have tried to source the most researched, effective, and affordable options currently on the market. You can check them out here: