Nick Maclaren spake thusly

What you need for the Agapanthus is a grub-axe (pick-mattock, or
whatever). Like a pickaxe, but with one blade 4" wide at right
angled to the handle. It will cut through the roots easily, and
Agapanthus will not regrow from them as I understand it.

I think I know of the implement you mean. Is it important to get all
the roots out of soil? They're so matted in places, I'd need to remove
half the bank!


The critical thing for clay is to loosen it as deeply as you
have the strength for. Compost or (coarse) sand are useful, but
less important.

Having looked at the site again, there seems to be a lot of... rock, or
at least, extremely hard clay, that just breaks off... not a lot of
"soil" at all.
--
Maggie