Q: I want to build a ring planter eighteen inches tall around a tree for planting flowers. Does it harm a tree to put dirt up that high against the trunk?

A: It can definitely harm the tree to have dirt piled around the trunk. The bark is usually thinnest where the roots flare out and bacteria would love to get into the cambium layer there to feast on sap. Soil (or mulch) piled around a trunk makes an excellent home for tree-attacking diseases. Construct your planter so an inner ring holds soil six inches away from the trunk in all directions such that it stays dry and keeps diseases at bay.