Air below 0°C is defined as Air frost, measured at a height of 2m (6ft). Ground Frost occurs when the air at ground level is chilled below freezing point. Ground frost is measured at 5cm (2in) above the ground. Hoar Frost the fluffy deposit of minute ice crystals on grass and brickwork, occurs on calm, clear nights when condensation takes place after freezing. Black frost, as the name suggests, is a thin sheet of frost without the white colour usually associated with frost.
Sedum covered in frost - this plant is as tough as old boots!
Frozen Bird Bath - don't forget to make sure you leave unfrozen water for the birds!