The zones used in this map are based on the system that the United States Department
of Agriculture uses.
In this zone hardiness map, the British Isles have been colour coded with seven
split zones, from 7a to 10a, in order to reflect the average annual minimum temperature experienced.
There is nowhere else in the world, at this northerly latitude, that experiences
such mild winter temperatures - Quebec, for example, at latitude 46° can experience winter temperatures
down to -30° C (-22° F). Our mild winter temperatures are due to the warming effects of the
Something that is worth a mention here is the fact that: even though some areas
in the UK might expect to receive similar winter temperatures to some parts of Florida, this needs
to be weighed up against the reality that winters are longer here.
The fact remains that the UK is situated on a much more northerly
so experiences a longer winter - in other words those winter temperatures, favourable though they might be, are more prolonged and the
day light hours are less. So, in actual fact, although the temperatures might seem similar, the
winter is more demanding on the cold hardiness of a plant.
More about UK climate and weather statistics from the Met Office