Very simplified: 1) Make sure that the growth medium is as close you can get to being sterile 2) Make sure that only spores from the desired mushroom is "plan

Very simplified: 1) Make sure that the growth medium is as close you can get to being sterile 2) Make sure that only spores from the desired mushroom is "planted" in the medium If done properly, the desired mushroom will outcompete the others, deploy its own defence mechanisms to keep others out.