1 part lava rock
1 part pumice (which is lighter and holds less water than lava)
1 part akadama (which will break down in about 2 years)
1/2 cup horticultural charcoal (per 5 gallon mix)
1/2 cup decomposed granite (per 5 gallon mix)
Deciduous trees use a small mix (1/16″-1/4″) and add 1 part akadama.
Conifers and high mountain species (notably Japanese white pines), use a medium size mix (5/16″-3/8″). This seems very large to look at, but prevents these trees from holding too much water. This enables the grower to water at the same time as other trees without fear of waterlogging. For appearance, place a final layer of fine mix on top of the soil.
For lower elevation conifer and water loving conifers, use a small mix (1/16″-1/4″).
Note: Proper repotting technique needs to be applied, otherwise this mix is not recommended.
This root ball has been grown exclusively in this mix and is completely colonized by mycorrhizae.