The lowdown on mycorrhizal fungi: What you need to know.

March 08, 2016

The lowdown on mycorrhizal fungi: What you need to know.

I hear a lot of claims out there regarding mycorrhizal fungi. This article is 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 over on the subject over the past 8 years, but I am always learning new things and will update the article accordingly. 

So what is mycorrhizal fungi? It's a fungi 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 and veggies, we want endo-mycorrhiza. The most widely researched species being glomus mossae 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:

  1. You want a product without trichoderma. Trichoderma is added to many mycorrhizal products on the market because it cheaper and has some more immediate plant benefit. However, a study out of Florida showed that it inhibited mycorrhizal infection. The big issue here is that most products have significantly more trichoderma than mycorrhizal spores, levels much higher than you would find naturally in soils.
  2. High phosphorus also inhibits mycorrhizal infection. Makes sense, right? That same study 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.
  3. It needs to be applied directly to the roots.
  4. It's a 1x application at the beginning of your plants life cycle.
  5. Reusing soil means having spores and hyphal fragments already in the soil and repeat applications may not be needed.
  6. Don't add it to teas. This related 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. 
  7. 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.
  8. Endomycorrhizal fungi do not produce fruiting bodies (mushrooms). If you see a mushroom it has no relevance to whether or not your plant has good mycorrhizal infection.
  9. 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 ecto-mycorrhizal 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).
  10. 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.

My favorite right now is WOW Mycorrhizae Pumpkin Pro at over 300 spores/cc.

If you wish to do more research and reading on mycorrhizal fungi, here's a good link to get started at Logical Gardener or pickup Jeff Lowenfel's new book, Teaming with Fungi.





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