I don't think there'd be enough of a difference to chance either zone 3 or somewhere really hot and dry - best to stick to e.g. your climate, which should be ideal, and not worry about the individual type.

Lucy
I have no indoor storage of any kind. Condo living has it's disadvatages. What I am looking for is a hornbeam that can take down to -15 degrees of damp cold and wind. Tree's like Trident are almost impossible to keep in pots and I don't want to have the same problem with a hornbeam. Most of my present trees have survived being buried in pine needles and snow.
Paul

Indoor storage? Where did that come from - I know I didn't mention it and a hornbeam needs to be outside.

Investigate C. caroliniana (American hornbeam) as one of the hardiest of hornbeams.

If you construct a box & put the open end against a heated building with your deciduous tree(s) inside, you can pick up at least a zone - maybe two if the box is somewhat insulated.

Al

Thanks Al
I have done that only I used a black resin concrete mixing box as a lean too and it does help. I have also stored under benches with a fence in the back round and with shelving or a tarp in front. Every little thing helps but I still rely on pine needles and snow.
Lucy
I was trying to explain my reasons for wanting to know which Hornbeam is the hardiest. You correct it did not come from you.
Paul

That's the hornbeam that's still alive after you've done everything wrong.

HO HO HO :) :) :)
Paul