Which zone are you?

Climate zones proliferate in the United States, but that’s hardly surprising in a continent that encompasses Alaska in the north and Mexico in the south. In the UK, our range is more limited. According to the US Department of Agriculture’s Plant Hardiness Zone Map, the coldest is zone 7, which includes the Scottish Highlands, the Cumbrian Fells, the Pennines and other areas of high ground situated well away from the coast. Here, temperatures regularly fall significantly lower than in other parts of the country and are slower to rise in spring.

Most of mainland Britain falls into zone 8, but where the sea has a steadying effect on temperatures then zone 9 is the designation. This covers the west coast of mainland Britain, stretching inland for quite some distance, along with south-west England, southern coastal areas and a narrow strip along the east coast of Britain stretching as far south as Flamborough Head. Cold easterly winds negate the effect further south. You’ll find all kinds of temperature regimes mentioned for these areas but as we all know, rules, especially in the case of weather, are made to be broken. Winter, we are told, occurs when temperatures drop below 6°C, but most of us regard the period between late November and February as being our winter.

It stands to reason that plants that originally come from the Mediterranean will find life in zone 7 challenging; they may cope in a good year in zone 8, but are most likely to thrive in zone 9 where even plants that are regarded as ‘frost tender’ may sometimes come through unscathed. Should you find temperature zones mentioned on the labels of plants that you buy from a nursery or garden centre, this is what they imply.

In the 1950s, when I was growing up in Yorkshire (zone 8), it was not unknown for our dahlias to be frosted in September. Nowadays this is rare, except in zone 7, and even there the first frost is more likely in October. In zone 8 it may occur as late as November and in zone 9 later still. It is not unknown, thanks to climate change and global warming, for gardens in zone 9 to escape frosts altogether. That said, it pays to be cautious and to offer protection to plants whose constitution is not especially rugged. Remember, also, to consider local conditions – the microclimate. Dips in the ground act as frost pockets, where cold air collects. Exposed knolls, even in milder counties, can exacerbate wind chill.

All of which should not send you into fits of apoplexy, for as long as you understand local conditions and the lie of the land you can take precautions that will see your plants through the tough times.