In this question, somebody asked whether Nicotiana (tobacco) ashes can be used to amend soil. The answer is more involved than simply considering the ashes as potash, because the ashes of specific species can contain harmful elements, molecules, viruses, etc.
Can Cannabis ashes be used to amend soil? I have a friend who follows the same pattern as in that other question, but they are smoking Cannabis instead. They save their ashes in a small tray and add that tray to their potting soil. Is this effective, harmful, both, or neither?
