m Ransley wrote:

Copper sheet , there is a copper sulfate impregated fabric sold for
gardners needing to keep invasive roots away , I cant find the link.
Copper sulfate poured in is a poison but if tree doesnt die roots will
grow. Sheet aluminum may work, it is cheap.,Very Heavy sheet plastic is
used for Bamboo containment, it is cheap.

There was an old trick to keep a freshly cut tree stump from sprouting
-- pound a few copper pennies into the stump. It has worked for 15
years on a tree I cut down.

NB: "Copper" and "Copper sulphate" are different. The former is an
element and the latter is a chemical combination. You cannot infer the
properties of copper sulphate from those of copper, sulfur and oxigen
which are the components of copper sulfate.