I just watched the Soil livestream from the library and I am still confused as to what to get.
Akadama that’s for sure, but is that it? Does 100% 1/4-1/16 Akadama go in to the container?
Ryan mentioned that his japanese teacher used 3-4 parts Akadama, 1 part Pumice and 1 part Lava, but is that what he uses as a base? How would that change for conifers and junipers?
Thanks guys!
I would assume that the Pumice and Lava sizes are also 1/4 - 1/16 if added?
The standard mix is 1:1:1 akadama, pumice and lava.
Certain times trees will go into 100% akadama, like deciduous trees or shohin.
Certain higher water moving conifers, will use the 3:1:1 mix of akadama, pumice and lava.
And yes, the particle size of all three components should be the same.
Most of the times the particle size is 1/16” - 1/4”. If more air is needed then it’ll move up to 1/8” - 1/4”.
Awesome, exactly the info I needed. 
How would I need to change my soil for a Juniper? Ryan mentioned to never let Akadama touch a Juniper.
Also, how can I identify a high water moving conifer?
Larch being high water moving for example. If you have a specific tree i suggest then to go into the library and watch the respective streams/features on those. helps also with cutting down the complexity in the beginning.
Word of caution on the Akadama though. It does not hold up to well in repeated freeze /thaw cycles. So in a CE European winter that can impair the soil and thus require more frequent re-potting or negatively impact percolation (if you have your trees overwinter outside and not in a cold storage/green house that is)
Very interesting. Could one avoid the Akadama problem with a heat bed for example?
For the topdressing, would it be required to add custom soil? Maybe smaller particles?
Or is the standard soil mix with some sphagnum moss enough to build the topdressing?
top dressing is done per the stream, no added soil or so in that layer.
heat bed yes, it prevents the freeze in freeze/thaw. But if you want to keep your trees on one all winter is a different topic.
The only tree that Ryan recommends to use no akadama is the Common Juniper. Juniperus communis - Wikipedia The experience with common junipers is that they are difficult to keep alive, and the water oxygen needs of this species is different.
All the rocky mountain junipers are placed in the soil mix with 1/4 inch screen being the smallest particle size. The exception is shohin or very small trees in very small containers. Then the 1/16th size is appropriate. Japanese and Chinese junipers do well with the volcanic soil mix and the ratio that works in your area depends on watering, local rainfall, and climate.
I look forward to corrections of my understanding!
Most of this knowledge is new to me and I am sure my understanding is going to evolve with more information and experience. I save the fines that are left from sifting soil to grow moss in trays and to create muck to use on stone and slab plantings.
Fir, hemlock and spruce are the ones I can think of off the top of my head. Usually I do what is recommended above, which is to try and find a video in the archive and see what Ryan says about soil composition as someone almost inevitably asks.