I am receiving a Japanese Mountain Maple late next week. I have done a bit of research on soil mixtures. This site recommends a 2:1:1 mix of Akadama, Kanuma, and Pumice.
Any recommendations/need to include a small bit of actual soil (dirt) to the mix?
Can anyone recommend alternative mixes and/or alternatives to the types listed above?
Thanks!

You can't grow anything in dirt. There is no need to add soil. Akadama on it's own is fine.

I have to say diatomaceous earth. It's a (depending on who you ask) better alternative to traditional soil mixes such as you mentioned and doesn't require anything else to be added. There are opposing views, however, as diatomaceous earth can be sold as cat litter which can put people off.

www.bonsai4me.co.uk/Basics/Basicscatlitter

Ed

BonsaiLearner wrote: There are opposing views, however, as diatomaceous earth

besides being used, as something, fury felines relive themselves in, except for the fact that it breaks down, really fast, and there are no standards, in it's manufacturing. (sort of turns to clay, sometimes).

Can you please tell us what the "opposing views" are.

Samantha wrote: besides being used, as something, fury felines relive themselves in,

If they do this in your pots with kitty-dama, they will do it in akadama too. I have NEVER had a cat in any of my pots. Cats that walk outside will not normally prefer a pot over a gardenbed.

Samantha wrote: except for the fact that it breaks down, really fast, and there are no standards, in it's manufacturing. (sort of turns to clay, sometimes).

It does not. I have been using it for 5 years and have not had any crumbling. The falling apart if a specific akadama problem, and the main reason why people in a climate with many wet thaw and frost cycles in winter are looking for alternatives. You do need to buy the right brand, zeveral are listed on the page linked before.

Samantha wrote: Can you please tell us what the "opposing views" are.

There are traiders who are worried they cannot sell their expensive akadama anymore, because they realize that many different substrates work fine and benefits of akadama do not warrant spending double or more for it. This creates conflict of interest and as such a lot of discussion occurs. lets not repeat it here. Enough has been written about this subject that can easily be found.

Samantha wrote:

BonsaiLearner wrote: There are opposing views, however, as diatomaceous earth

besides being used, as something, fury felines relive themselves in

With bonsai, that's not an issue, unless when you have really tiny cats.