Q: I will be planting a tree on a steep slope. How much of the root ball should be exposed on the up and down sides of the hill?
A: None! Planting a tree on a slope correctly is a laborious process because the root ball must be kept level with the surrounding soil. The soil where you are planting is sloped – but that doesn’t mean you should plant the tree at an angle into the slope. Nor does it mean the root ball can be left “halfway in – halfway out” as you have suggested.
You have to terrace the slope to make it flat for an area five feet in diameter. The tree can be planted in the center of this flat area. Since you’ll have to “cut in” to the slope to form the terrace, use a couple of firmly anchored treated timbers to hold back the upper slope. It would be a good idea to use more timbers below the terrace to hold it back and to protect the lower side from erosion.