Inner ring MUST have a layer of large river stones for air +water to get to trunk, otherwise it will suffocate + kill the tree. The soil will support small shallow rooted plants like Allyssum or Primrose.
UP-CYCLED BIKE PLANTER: Don't throw it - grow in it! An old bicycle can be repurposed with micro container gardens and even used as a trellis for a climber like a grape vine. Mounted on a fence, you can create your own garden art feature. More ideas & tut
13 Garden Arbor Ideas to Complete Your Garden Aesthetic