Is it lawful or unlawful to plant trees by gravesides?

It is permissible to plant trees by gravesides provided they do not obstruct the path of those following the funeral procession or those undertaking the burial. Otherwise, it is impermissible. The planted trees must not be of the kind that have a divaricating root structure. The roots must be vertically oriented so as not to destroy or damage the graves.
And God Almighty knows best.