According to wikipedia some plants are badly affected by juglone and some
not at all affected.(No examples of the latter are mentioned) Does anyone
know of anything in the 'not affected' category that might be usable to
patch the hedge?

It's crap. Firstly, the tree that causes that effect is Juglans nigra,
not Juglans regia and, secondly, the effect is fairly minor - indeed,
I don't even know what plants are definitely affected. My mother had
shrubs growing under a J. nigra, and I have Hamamelis, Viburnum,
Helianthemum and Berberis growing under a J. regia.

What will have happened is that the tree took the water, nutrients and
light from the hedge, and it probably failed because it was out-competed.
Brambles and ivy are undershrubs and are adapted to that. I am not sure
what hedge plants do best as underplants, but I have seen yew and holly
growing as such in woodland.


Regards,
Nick Maclaren.

Yes, I noticed all the links I have been given were to American sites about
the black walnut. They do include many suggestion for trees and shrubs that
don't mind it. I couldn't remember which species I had, but I have checked
and it is Juglans Regia fortunately. However there is a red oak to one side
and a field maple the other, and their stretches of hedge are not suffering
as badly. My husband is blaming it on the big leaves of the walnut choking
the base of the hedge! He may be partly right. I have room to try a variety
of things but also sometimes have sheep next door so I have to be a bit
careful.
Thank you for your help, and thanks also to Jeff for the other links.