What are UK hardiness zones and why would you care?

Pansies, anemones and violas in a light dusting of snow

Did you know that gardeners around the world use a reference scale called ‘hardiness zones’ to assist with growing plants?

The scale was originally developed by the US Department of Agriculture, and ranges from 1-13. Areas are graded according to the average minimum winter temperature in the region over 10 years. As a general guide, 1 = very cold (think -50 degrees celcius in Northern Canada) and 13 = tropical (lowest temperature 18 degrees celcius).

Of course, soil type and sunshine make a difference within a region as to what will grow well in a garden, but understanding hardiness zones is a great starting point when you want to begin to understand what will grow well in whatever space you have.

The UK is generally accepted as being in zones 7, 8 and 9, with some parts of the Scottish Highlands also falling into Zone 6. As a general rule, if you aren’t in the mountains or on the coast, you’re most likely to be in zone 8, but here’s some more detail:

Zone 6 – the interior Scottish Highlands, as far from the coast as you can get, lowest temperature is likely to be
Zone 7 – elevated land far from the coast, specifically the rest of the Scottish highlands, and central Welsh highlands.
Zone 8 – North-East Coast, everywhere else that isn’t mentioned in zones 6, 7 and 9.
Zone 9 – most of Ireland, most UK coastal areas, with the exception of the North East coastline which is Zone 8.

So if you have perennial plants outside in spring and autumn/winter, it can be helpful to know which zone you are in so that you know how likely it will be to frost in your region, and so that you can take appropriate action to protect your plants, if needed.

Side note: USDA hardiness zones are not the same as the hardiness scale devised by the Royal Horticultural Society, which refer to the hardiness of individual plants and not hardiness zones themselves.