In article ,
Roger Van Loon wrote:
Nick Maclaren wrote:

Having been prodded once too often by this, here is a draft of a
climate FAQ (including remarks about USDA zones). Comments
welcome.

Hi Nick!
Well - having been prodded by some of my UK gardening friends -
I don't agree with everything you say (you didn't think I would, did
you? :-))
But overall - most of your FAQ is very true and useful, really.

Thank you.

But - you said "Comments welcome". I will hold you to that.
OK, Nick, before point it out, who am I to comment? It's true that I'm
not living in the UK permanently - but I spend lots of time in the UK
every year, I have very many gardening friends over there, and (sorry
if I may sound arrogant) I think I know practically every important
public garden between Tresco Abbey and Inverewe. And I have a very
good idea of the plants that are grown there, and their growing
conditions. How many of you can say that?

Probably not many.

Now, there is just one basic point of yours that did raise my
eyebrows:

Q: Are they relevant to the UK?
A: (snip) And, of course, the USDA ratings of plants are the
USDA zone at which they will grow, when grown in the USA.

What on earth has given you that idea? The USDA Z* zones (as given in
all recent UK plant dictionaries/encyclopedias) have nothing to do
whatever with the US situation. They just indicate average yearly
minimum temperatures (and, as has been said before, in my opinion they
just relate to the natural habitat of the plants).

Roger, PLEASE read my postings before responding! In the above, I
said "the USDA ratings of plants". A plant doesn't HAVE an average
yearly minimum temperature. What I said was and is correct.

And, Nick, I wonder if we have not been talking on the basis of some
misunderstanding, all along.
For example, you say:
There are also plants (e.g. Albizia julibrissin, Daphne genkwa)
that abosolutely must have enough summer heat to ripen their
year's growth to survive the winter. These are rated at USDA
zones 6b and 5b, but are seriously tender in the UK.
Where in heaven did you get those ratings?
Albizia julibrissin, just to follow your specific example, is rated in
all of my recent UK books as Z7 - not at all Z6 or Z5 (and, by the
way, I have seen nice specimens in many places in the UK - as was to
be expected).
So, I certainly would like to know your sources.

If you look on the Web, almost all references to Albizia julibrissin
are hardy in zone 6 - I was being conservative with zone 6b. Bean
describes it as not hardy in the open at Kew, the RHS Encyclopaedia
describes it as half hardy, I have grown it for 2 years and it has
suffered badly both winters (as the summers have not been hot) and
it may not recover this year. Maybe your books have fudged its USA
rating a bit to hide the USA/UK differences?

I was referring to Daphne genkwa as zone 5b.

Now - just a last basic point.
More and more, I am getting the inpression that the reactions in this
newsgroup against the USDA zone system are "just out of principle" -
and hardly anyone has tested it out for himself. Am I right?

No, you are left.

If I'm wrong - could you give some specific examples please? (I mean
Z7 plants that were killed by frost this winter - not the mildest
one?)
I think it might be an interesting discussion.
But not for me - I'm signing off.

Then why ask? But, for anyone else that is interested, I can witness
the delicacy of Passiflora incarnata, Albizia julibrissin and a large
number of USDA zone 7 plants.

I tend to use the Sunset book myself, when referring to USA conditions,
but even that needs a fair amount of interpretation.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679