My dear neighbor and I are planning to plant a mix of rhodos and kalmias along our common fence line. However, we observed that there is a walnut tree (likely a black walnut) only about 25 or 30 feet away from our intended site. Having read several threads on this forum about the incompatibility of rhodos and walnuts, maybe this is not such a good idea.

However, dear neighbor suggested she would like to get rid of the disreputable walnut anyway (nuts dented her car) and that might solve the problem.

Question #1: Will the offending substance in the walnut's roots survive the tree's demise? If so, what is a respectible mourning period?

Question #2: One of the older threads suggested creating a raised bed with landscape fabric underneath and mulching new plants in well. Has anyone had experience or knowledge of success with this approach?

P.S. I have a lilac growing not 15 feet from the despised walnut, and it does fine despite info that lilacs are also incompatible with walnuts.

Your advice much appreciated.