We have a tanyosho Japanese red pine planted a few feet from a 1' high retaining wall. We also have a couple of Japanese maples--an Emperor I that is 3' from a 2' high rock wall, and a Waterfall that is 18" from a 1' high rock wall that is above another terraced retaining wall.
As these trees become larger, where will their roots go? To the edge of the rock wall and dry out? Or will they go down to the level below the rock wall seeking water before they get to the edge of the wall?