Thank you.
I am currently writing an article on the actual cultivation of mushrooms in containers, I am hoping to complete it soon. Unfortunately, many mushrooms do not seem to take well to container cultivation and my experience is limited only to those that have been successful, although I continually experiment with new species.
Fortunately there is a huge industry that cultivates mushrooms for sale and consumption, so I have the experience of these growers to build upon.
Like the fruit on all fruit trees, the mushrooms (in a sense, also a fruit of an organism) size and shape is determined by genetics and can not, to my knowledge, be reduced in size. So we must choose mushrooms whose size will not overwhelm the container and that are best in scale with the bonsai. Luckily, mushrooms come in all sizes and colors and even many different shapes, so there is a vast range to choose from.
On another topic Mxia, could you please take the time to read our user name policies located at
http://artofbonsai.org/forum/viewtopic.php?t=403
Will