Myco Grow

I am kind of doubtful that it would have an effect, especially that quickly. Most terrestrials have a very specific symbiont and the mycorrhiza you have applied are a type not associated with orchids. That said, the presence of such micro-organisms can keep the nasty ones at bay however they may also attack the orchid mycorrhiza.

Your Diuris and Thelymitra don't really have a requirement for a fungal symbiont once they are mature so there should be no ill effect. Caladenia and Leptoceras are more mycorrhizal dependant so I'm not sure how they will progress. Normally in these genera the mycorrhiza will interact with the plant at the "collar" which is why you should try to keep this part of the stem attached to the tubers after they go dormant.

What was I thinking!

I should've conducted a true experiment before making such conclusions.

Too bad affording several of these won't be that easy considering how much it costs to get the proper paperwork done and how much it is to have them shipped here.

When Nesbitts sent the Leptoceras and Caladenia, he left the neck on, but they all rotted. I'm not sure why. Maybe, because fungus gnat larvae got to them or something, idk. One of them had little holes in them.

I'm only left with the Thelymitra aff. frenchii and Diuris behrii

While the mycorrhizae in commercial fungi mixes aren't orchid fungi, I've come across a few plants from some of the German growers on the terrestrial forum that have been grown with Trichoderma etc. If I'm understanding their reasoning correctly, their using them to out compete other fungi in the pots so the plants can stand on their own two feet without the threat of other fungi in the pot becoming pathogenic. Of course I'm Australian so I'm not ready to cut the mycorrhizal apron strings just yet but I can't argue with them when they're growing Caladenia this way. Adding commercial fungi mixes isn't necessarily a bad thing.

There's a very good explanation for this; they're Caladenia. ;) Even though they're the easiest Caladenia species to grow, they're still very easy to kill.

I put Caladenia in a very sandy mix to ensure they don't stay too damp. "Diluting" the organic material with sand also seems to help prevent rotting.

I also don't usually pot my Caladenia up until they show signs of life. Introducing too much moisture before this happens almost always leads to them rotting.

I have to admit it took me a couple of years to work this out and I have lost a few in the process.