In message , Nick
Gray writes

What size would you recommend?
2-3 years is pretty good.

Hornbeam grows 2-3ft per year, so it depends on how high you want your
hedge. Hornbeam is ideal in wet clay conditions, whereas Beech prefer
well-draining soil.

No one told our beech hedge that. It grows perfectly well on cold wet
clay. Looks nice and golden at this time of year too. Hornbeam grows
better and has nicer berries though.

When pruning a new hedge, don't cut the leading branch (with the exception
of hawthorn) until it has reached the desired height, in early autumn cut
the sides of the trees to encourage a dense hedge.

Planting a long hedge in runs of about 2-3m the same species looks nicer
than having 30m of all the same unless it is a very formal garden.

Regards,
--
Martin Brown