I realize Denise said she was a master gardener.
Walnuts are not produced until the tree is at least 8 years old, by then the roots would be long enough for the juglone to affect plants around it, unless the plants are tolerant, which I do not believe tomato nor the lilac would be tolerant. Black walnut trees are also not rampant self-sowers, as the black locust is, which looks similar. I have lots of experience with black walnut, as we have two very old black walnut trees and also quite a few locust, which self seed often and can appear similar to walnut when young trees.
Edit: My last comment was related to the fact that some people appear to have multiple log ons and No-Tech answered that yes, it was a black walnut.
