In our circular driveway we have a border around a 20' tall Queens Crepe
Myrtle tree made of a few 4x4 landscape lumber tied together with metal
angles. We are going to change that to using retaining wall bricks.

One question is the wall would be a foot higher than the current height of
the 4x4s. I am thinking may be I need to fill in some soils inside the ring
to bring that up 6 inches or so. Would doing so hurt the tree in any way,
adding 6 inches of soil and another 2" of much at it's base?

I am going about 4 bricks tall, each brick 8 inches tall. The guy I was
talking to that may help me install this says there is no need to use mortar
in between each brick all we need to do is to have some sand base and stack
them up. Is that the case?

Thanks,

MC