Anne Middleton/Harold Walker wrote:

"Alan Holmes" alan@holmes-
For some inexplicable reason you americans seem to overlook the
fact that we do not have 'Zones' we have 'weather'!
Alan

You may not have "zones" but you surely have regional differences......I
suspect that a number of plants can be grown in the South West of the UK
that cannot be grown up in the north country.......zones/regions.......a
rose by any other name is still a rose......being a Yank intruding upon your
site, albeit a newcomer one, I could be very wrong.....to that I readily
admit.

The problem is that with the combination of Gulf stream and westerly
prevailing
winds you can get some incredibly anomolous warm spot microclimates.
There are
places on the Western coast of Scotland where hardy palm trees grow in
the
streets - eg Plockton (latitude 57.3 and which conveniently is online)

http://www.plockton.com/

That is even further north than Edmonton in Canada. In general yes as
you go
further north you get less winter sun and shorter summers. ISTR RHA does
a nice
map showing a graphical representation of it with week offsets of
planting and
flowering times from Wisley.

Maritime climates do not match USDA frost zones at all. The influence of
the
combination of surrounding seas and prevailing wind (or lack of it in
winter cold snaps)
absolutely dominate the UK weather. The Sunset climate codes for the
Pacific NW
can be useful but even they need taking with a pinch of salt.

By all means specify the minimum temperature that a plant can tolerate
for the
US market, but when that is not the main factor that determines the
plants survival
in a UK winter it is pretty misleading to do so here.

Some rare plants that are fully continental US frost hardy are amongst
the
hardest to grow in the UK because they need to be cold in winter but
will not
tolerate any humidity when they are dormant.

Regards,
Martin Brown