On the basis of minimum winter temperatures, we fit in a Zone 8 or 9, but we can't grow their Zone 8 or 9 plants because of our lower summer temperatures and shorter growing season.

Our temperatures are governed more by the Gulf Stream which keeps us warmer than we would otherwise be this far north. We also have lower light levels than most places in the US.

There is another system which works on temperatures, and I think that makes us a Zone 4 or something.

When we were allowed to swap seeds with people in the US, I often found they wouldn't want to swap if they were in a Zone 4, or if they were in a Zone 8, they wanted to send me palms and citrus. So I don't use the zone system any more.

As to Crazylady's points, the zones are based on winter minima, and apply everywhere, not just the US. The problems she details refer to the much hotter summers of the eastern US; the zones in Britain correspond very closely in growing season conditions to the same zones in the Pacific Northwest (Oregon, Washington, southern Alaska, and also British Columbia in Canada).

Resin

That should of course read "Here's a UK and Ireland zone map"

Resin

Of course as they always say: "past performance is no guarantee of future performance"! Most of the country has had warmer than average winters over the last ten years, and that trend may or may not continue. Last year's "cold" winter was the coldest for ten years (for most places by most measures) yet was still warmer than the longterm average. Next winter may be like 1995/6 or 1981/2, or god forbid 1962/3, and all your lovely zone 9 plants will be zapped into a big plant graveyard.

I'd hate to see the UK get as zone-centric as the US. It's a half-decent idea but local micro-climates are SO much more significant.

Since you live in a country with only a few degrees difference in winter temperatures for all main population centres, with microclimates perhaps more important even than which end of the country you live at, you may not ever feel the need to define how cold your winters are. We are spoilt by the simplicity that "frost hardy" will survive, "not frost hardy" will die. But please spare a thought for people who need to know, by a simple widely understood method, whether a particular plant will freeze to death or not in their back garden. Do you know whether a Brunnera is cold-hardy in Cleveland?

Not only do I not know if a brunnera is cold-hardy in cleveland, I don't know what a brunnera is. I do know that the imported white cabbage-moth (for instance) runs rampant in the mid-atlantic, probably from about zones 8 up to about 4.5. The beastie can't survive northern Vermont winters and does not establish in most of Florida. A great many other bits of useful info can be associated by zone.

I should think it might be useful to increase the zone-scale for an area such as the UK. How about adding decimals? Perhaps northern scotland or the pennine elevations would be high sevens, the midlands mid eights, cornwall mid nines, for example. 7.5 thru 9.5 gives twenty graduations - twenty zones.

I do wonder if many people in the UK really appreciate how much climate variation does exist across our small country, even across just England. Rainfall varies from barely 20" to about 40" in lowland populated areas, and to more than 100" in west-facing hilly areas. Winter lows vary from barely freezing in extreme western areas to -10C in central lowland areas, and far below that in upland areas. Summer highs are 5C-10C less in northern England than in inland areas of the south, and even less in Scotland.

Worth noting that the 2005/06 winter was the coldest in most of Britain for over 10 years, but was also slightly warmer than the long-term average.

Whether we will ever get another really cold winter like 1981/82 in northern Britain, or 1986/87 in southern England (-7°C on Scilly), or 1962/63 for old-timers, again must be open to significant doubt.

Resin

I was always surprised at the relatively small annual precips recorded in Gilbert White's journal (low 30's seemed to be average), as england is generally thought of as a wet climate. Those numbers would be considered drought years in the eastern US. Southern england must also have been much colder then, because his records of winter temps are very similar to what we experience now in southern new england.

Conversely, Cambridge in the east of England only gets about 65cm/year.

Gilbert White was living during the 'Little Ice Age'; southern England was probably zone 7 back then. A particularly severe winter in 1740 was recorded as killing nearly all the Cedrus libani in Britain, which probably means a fairly widespread -27 to -30°C (as that's the temperature this species suffers significant mortality). That winter "the Thames was frozen for about eight weeks, and Thames shipping and London Bridge were damaged considerably by the ice"; "deep snow fell about Christmas in Norwich, which remained on the ground until March".

The 1715/16 winter was similarly brutal, also with the Thames frozen for 2 months with ice thick enough to hold a 'frost fair' on the river; "ice on Thames in London was lifted by 4.3m by a flood tide but did not break".

Resin

That's still a fairly standard rainfall for most lowland areas of England. The reason England is "wet" with such rainfall is down a number of factors: consistency of rainfall throughout the year with a completely dry week being somewhat unusual; moderate temperatures with the average high around 70F in the middle of summer; relatively low solar insolation in summer since the whole country is further north than anywhere in the contiguous states and cloud cover is high in the marine climate; cool humid winters with very little sun mean that all soils are generally saturated by the end of every winter; and aquifers, rivers, and lakes are well fed from winter rainfall and from extra rainfall on high ground.

I once read an amusing account of some of the first settlers on Cape Cod (it wasn't meant to be amusing, but is so to someone familiar with gardening in this area). It was their first spring here, and when one of the typical early spring heat-waves came along, they figured the climate was the same as back home. They planted all the crops in early march! The amazing part was that most of the stuff germinated and even produced (even the maize), because it happened to be one of those 1-out-of-50-year warm springs. In subsequent years they nearly starved to death.

I guess that was before the 'little ice age'.

I have some :)