Hello. I think thats an amerian idea

go to www.uk.gardenweb.com/forums/zones/hze1.html
The US covers everything from the desert southwest to the Canadian border and since plants have different requirements, someone came up with this. Since it never snows here, why would I waste time and money on a plant that requires those low temps. It also lets you know that a plant won't survive outside if you have those low temps and it is more topical. Most of the UK is zone 8, except the warmer west coast which is zone 9.

thanks Wyl very interesting

Hello

This is American with the USA being such a vast country and having so many different climates they have split the country into plant hardiness zones so you know that they are planting the correct plants for the part of the USA they live. The zones start at 1 and go through to 11 Alaska is a good example of zone 1 where the winters are very cold. Hawaii and the other tropical/desert places are zone 11 where the weather is hot all year round it is very complex because individual areas of 1 state can be in different zones. Do a Google search and find a map and you will see how complex it is.

Steve

thanx steve you learn something new everyday

In the USA, though, we have a problem with the zone systems which are solely based on winter lows. According to the USDA zones, Tacoma, Washington, Phoenix, Arizona (my garden), and northern Florida are all in zone 9. As you can imagine, there is very little overlap in our plant palettes! Be thankful that you don't have to deal with this in the UK!