Thanks for the suggestions. I will certainly look at Ercilla.
For now, I have stuck a Passiflora incarnata (from seed) and will
see if it overwinters. It is only herbaceous, anyway, so I need
a more permanent plant.

I find the behaviour of clematis odd. Some of them certainly don't
mind absolutely dessicated soil, if they can get their roots down
to water. The tops of the chalk downs can be really waterless,
and C. tangutica also seems very happy with any (UK) amount of
drought. But others do OK for a bit and then tend to drop dead.
Weird.


Regards,
Nick Maclaren.