Duncan wrote:

I would quite like to use hornbeam for a hedge. Will it grow in a damp heavy
clay near Thirsk, Yorkshire? The predominant tree species adjacent to where
I'm thinking of putting it is alder. Oak and Yew are also present.

It grows OK on our heavy clay soil twenty miles north of you. My
neighbour had a large hornbeam tree in her garden. Beech, cotoneaster,
pyrocantha, privet, hawthorn, sloe and holly also grow pretty well here
too. The first season is probably critical to them establishing.

I don't know if hornbeam keeps its leaves in winter if grown as a
hedge. (Beech does)

I prefer hedges in patches of ~3m for each species to have some variety
of texture and colour. Pyrocantha, holly & cotoneaster are very pretty
at this time of year.

Regards,
Martin Brown