sodium hydroxide best i can come up with. if you tried to grow in it, that would be your growing medium.
Not at the moment, haven't looked into it.
why do you think so many bag soils put ph buffers/stabalizers in their mixes (usually dolomite lime or similar)? and there are premade soils with different ph's directed towards different plants. i.e. 'acid loving plants', like cannabis.
because ph matters to plants.
I can't even fathom implying that ph doesn't matter in any growing medium, it's beyond me.