In article , Roger Van Loon
writes

They do??
The ones I have don't!!

Nor mine!

They must be totally out of date then.

Now, hang on a minute there.
Hold on to your horses.
What in hell's name do you mean by 'out of date'??
I never heard such a stupid, nonsensical expression when referring to
gardening books!!!!!!!!!!!
A plant which needed conditions x, y and z a couple of centuries ago,
still needs conditions x, y and z today!!!!!!
I regularly use my late father in law's book on pruning shrubs -
published in 1966 - never found one better. In fact some of the old
remedies are far better than modern stuff - much more environmentally
friendly.
I have two RHS books, one published 1999 and one 2000, several Hessayon
books all of which I find invaluable and not one of them so much as
mentions USDA hardiness zones. Why should they waste time and effort
writing stuff which is of no use to us? Incidentally, while at a garden
centre yesterday, I had a look at a few books - didn't find any
references to USDA hardiness zones.
I agree with other people in this thread - if our authors are now
including USDA hardiness zones in their books, it has absolutely nothing
to do with the relevance of that information to UK gardens but
everything to do with profits and markets for the publishers.
--
Jane Ransom in Lancaster.
I won't respond to private emails that are on topic for urg
but if you need to email me for any other reason,
put jandg dot demon dot co dot uk where you see deadspam.com