Strong and vigorous tree roots can cause damage to retaining walls, so it is best to plant them at a safe distance from your wall. The same goes for some shrubs – you would be surprised how deep these roots can go! A good rule of thumb is to plant your tree or shrub the same distance away from the wall as the height you expect it to reach. So, an ornamental tree that will grow to 10 feet tall should be planted at least 10 feet from your retaining wall.