My Buttonwood soil is Metro Mix 500, a peat/coir based commercial mix. I
find they do much better in this than in the traditional well drained bonsai
mix.

That may be true in Florida. I think I killed 2 buttonwoods (ouch!) by using an
overabsorbent so-called tropical mix. My first buttonwood did fine in a more
open bonsai mix until it was stolen.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"A tree never hits an automobile except in self defense." - Woody Allen