I often get myco like that. If it likes the conditions it will thrive in the pots. I don't even bother transferring any to new pots now because I found that it is already on the roots of the trees and just regrows. It even transfers to new pots without any help and ends up in all seedling trays in less than 6 months.
Just because you can't see it does not mean it is not there. The mycelium is harder to see when the soil is wet and in certain other circumstances.
Also remember that it only assists the tree obtain nutrients when resources are scarce. In a well fed pot with plenty of plant available nutrients the tree is quite capable of obtaining nutrients directly and does not need to rely on the mycorrhiza.
I find that you can have too much. It tends to make the soil a bit hydrophobic so watering properly can become more difficult when the pots are packed with mycelium.
A healthy Scotts Pine that I wanted to change the pot and planting angle today. My conifers always have a good Mycorrhiza colony and all I ever do is make sure to inoculate the new soil with a little Mycorrhiza that I scrape off when I start. When I popped this guy out of it's pot I said, wow that's quite the colony, but when I started removing soil I realized that it was basically a giant cake of fungus and roots.
Drainage was still ok, not the best, but nothing that would worry me. I put a small amount in the bottom of the new pot before I put the tree in, and I never wash the roots so I'm sure it's got a good start. The tree seemed really healthy and I'm sure hoping it helps with the root work that was done. Anyone else have so much Mycorrhiza packed in their soil?
