Plants can be described as hardy, winter hardy, half hardy and tender and it can be very confusing to know what to do with your plant, and whether it can survive the winter without protection.
A number of factors will affect hardiness – the age of the plant, moisture, or how recently it was planted. Many plants survive short exposure to a given “Hardy To” temperature – below this they will die. If exposed to prolonged low temperatures around or below 0°C, the plant will also deteriorate. Additionally, if the soil/ compost is waterlogged, many plants will also struggle. This is often more important than the temperature. That said, many exotic plants that are known to thrive in the UK will become more tolerant over the coming years as they establish.
For more information on plant Hardiness please see the RHS hardiness rating here