"Mick" wrote

I split and re planted last autumn a Hydrangea bush that was
originally from my late father's garden, so it is plants' that are of
emotional and general value to me.

They have put on good growth this year but not flowed, nor did I think
they would.
Should I cut the new growth back this autumn or in the spring or just
leave them?

I understand they are normally left to the spring, but if possible I
would like to see them flower next year.

Leave trimming them back until the spring when you can see new growth and
know where to cut back to. The top growth will protect the plant during the
winter, with dead flower heads it's an even better protection. BTW if you
cut them back to the ground each year you won't get any flowers, you just
trim back to a suitable healthy bud on last years growth and take out some
of the older wood.
--
Regards. Bob Hobden.
Posted to this Newsgroup from the W of London, UK