I'd not want to put in a plant which would grow to the size of the opening. Growth would be restricted, at least until pressure bursts the board. City
This mycoboard reminds me of trees in metro areas planted in a concrete
sidewalk. There is a small square space which is open to the soil for the tree to grow in.
The size of the board is not so huge that deep roots
could not get water. Drip irrigation could provide the needed water for smaller roots
I suspect the board would dry out, particularly on the exposed side. If the board was mulched it would better retain moisture which would further the life of fungi.
This device is neat and clean and tidy. I betcha the Beautiful People
would buy these up by the dozen for their shrubberies.
Down here boards in my beds dont last long. I've used a few different types of stock. 1" white pine makes it for 2 seasons. 3" thick rough cut hickory
has made it for 4 years. Sweet gum made it for 5 years before crumbling. I've had weeds growing from these boards when they get going with decomp.
In the vid, I see lichens on the prototype shown. Can the boards be innoculated to give them a head start with establishing mycorrhiza, and is there a practical advantage in the effort?
A 2 piece unit would enable use on an existing plant.
Square vs Round Hole
Looks like you made 4 saw cuts in production. I'm thinking a drill press with a hole cutter would speed things up.
The prototype shown is quartersawn. If you produced some crosscut units it would be possible to make a comparison as to which method offers advantages. I think crosscutting would allow moisture to move through faster, but mycorrhiza would also move through faster.
I think this would allow weed growth.