This is a nutrient deficiency? on Hydrangeas Nitrogen deficiency is seen as yellowing of old leaves, Iron chlorosis is found on new leaves. An alkaline pH of 6.5 is best for white and pink mop head Hydrangeas so if you do a soil test of both areas you may find why the answer to why one is growing so well?

Drc, pH 6.5 is slightly acid. 7 is neutral, over 7 is alkaline.

That leaf looks distorted to me, and coupled with the yellowing, more like a viral infection. Where are you attempting to grow new hydrangeas, I mean what conditions - in a pot, in the ground, in full sun, in shade? Have they all looked like this and how many have you tried?

The buckling looks viral to me as well, but I don't know of any viruses that affect Hydrangeas.

Viruses can affect any and all plants, Beattie, but its more likely on some than others - peas, for instance.

Sorry Beattie I meant a soil Ph of 6.5. I am sorry if its a Virus. I never had a virus on mine but from time to time they needed a good feed to perk them up. I found they behaved better, I also found an Ericaceous compost suited mine.

Thanks for the suggestions.
I'll follow up on the pH check and see if that tells me anything.
I've probably tried growing about a dozen hydrangeas three and a half (!) of which are currently surviving.
None are south-facing but they all get some sunlight. The soil is of pretty dense clay-like character so drainage is probably poor and the tendency to dry out - high.
I have doubts about the lack of nitrogen suggestion because other plants (like fuschia and honeysuckle) produce loads of greenery.
It's generally difficult to grow new young plants in my garden but if one can nurture them through to the 3rd year then they seem to survive OK. I still suspect it's some little wee beastie devouring them but that there is a'critical mass' of leaves beyond which the plants can 'learn to live with' whatever is attacking them.