A black walnut tree is growing in a natural area just beyond my lot line. This is the first year it has produced nuts. I have a row of arborvitae as a border at the end of my lot and not far from the black walnut. Some of the flowers (phlox and monarda) in that area have not done well. Can the arborvitae be harmed by the black walnut roots? That tree is not on my property.