How on earth do you kill it off completely- I planted one on mil grave and it has taken over - from an innocuous looking pot plant to a monster. Everyone is complaining about it and I am the villain of the piece! Have chopped it within an inch of it’s life several times but it bounces back following year. Is there something I can treat it with - not bothered about strength as it’s a barren graveyard. Help please - before they stop talking to me...