@deFharo,
Now I understand the question. To answer if mycorrhizae can grow in mulch I would say yes, it can grow in mulch in certain conditions. This is all anecdotal from my experience and at least one source, Chris Trump who seems to be very knowledgeable in Korean Natural Farming, KNF is where I took my ideas from and applied them to my projects.
To start, Chris Trump’s way of collecting mycorrhizae or IMO from the forests included sifting through the top layer of natural leaf mulch around the base of mostly old growth trees, he would collect this and use it to boost his collection of Mycorrhizae. I took this idea to a mulch pile from last year when we ripped out lots of bushes and ground up roots, leaves, stems, trees, and basically all manor of plants; one possibly important note there is we literally ripped the plants from the ground so roots and all where mixed when the material was shredded.
As this material composted I noticed a layer about 4”(10cm) into the mulch that extended some 4”-6” (10-15cm) into the pile that was rich in what appeared to be mycorrhizae. I grew this mycorrhizae into IMO 1 then IMO 2
I watered the IMO 2 in with seedling transplants and I noticed a significant amount of nice fuzzy roots and fuzzy mycorrhizae when I re-planted these.
Although there was nothing scientific about the method I would say the Results were good and I would do it again.
For the Spent Brewers grain this I nearly observed after using it as a mulch layer it was quickly taken over my fungus and made a good growth media for it, from there I did a larger batch with IMO 2 and was fairly happy with the growth on it. I believe Chris Trump uses Hazelnut shells in his video from his IMO 3
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