It appears that one of the last things the previous owners of our
house did before moving was to empty the contents of a compost bin
into a corner of the garden.

This was right beside a mature mix of hedges/shrubs, which have now
started to thin and die. I am assuming that it must have been
immature/unfinished compost (thanks Google!).

The hedging in question previously provided a substantial amount of
privacy from our neightbours, so we really need to save whatever we
can.

What is the best way to remedy or limit the damage done by the
immature compost?

Thanks