Hardiness Zones

Knowing your climate zone and information about average frost duration can be really helpful to gardeners.
With that in mind, and considering the size of the huge North American continent and all its differences, the US Department of Agriculture divided the country into "Hardiness zones". Once you know the zone which corresponds with where you live, you can then match it to the hardiness plant rating, which is part of standard information given to gardeners in the USA.

These zones are also applicable to the UK and to the rest of the world, so you can formulate a basic idea of the lowest winter drop to expect in your own area.  Most of the UK falls into 3 zones: 7,8 and 9.

Zone 7 : Coldest - Central Scotland. Average annual minimum temperature: -12.3°C (10°F) to -17.7°C (0°F)
Zone 8 : Most of England and all Scotland (except zone 7). Average annual minimum temperature: -6.7°C (20°F) to -12.2°C (10°F)
Zone 9 : Includes a strip all round the west, south and east coasts and East Midlands. Average annual minimum temperature: -1.2°C (30°F) to -6.6°C (20°F)
Zone 10 : The toe of Cornwall and Scilly Islands, nearly frost-free in all but the worst winters. Average annual minimum temperature: +4.4°C (40°F) to -1.1°C (30°F)

Zones 7 and 8 typically correspond to Hardy plants. Zone 9 would suit Frost Hardy plants and zone 10 would be ideal for Half-Hardy plants.