Will Installing SemiCircle of Boulders for Wall Under Maple Tree Damage Roots

Asked May 22, 2020, 4:15 PM EDT

Hi - I'd like to build a semi-circular rock wall underneath the maple tree in the photo (on the downhill side, to retain new soil I'll install for planting groundcover and hostas). But would the weight of the boulders in the wall, harm the roots (for example, compacting the soil and cutting off the flow of water through the roots)? I don't want to permanently damage this beautiful tree. Thank you for your advice.

Washington County Minnesota

1 Response

I am more concerned about the amount of soil you plan to put over the roots than I am the "boulders". Roots need to breathe and that is why they are near the surface. If you put too much soil over them they will die from lack of oxygen.

From the picture it doesn't look like there is that much of a slope. If you want to raise the downhill side you can get away with 1-2" of soil, but mix in some compost to lighten it as much as possible.

With 1-2" of soil you can use smaller stones to ring the planting area. Boulders says to me that you were planning to level the bed to the uphill side and that would be simply too much soil, plus you would have to bury part of the trunk and that is not good for the tree either.

When planting, purchase smaller plants so that you won't injure the roots by digging large planting holes.