Ground frost occurs when the temperature of the ground falls below freezing point (0ºC/32ºF) and air frost occurs when the temperature of the air falls below freezing point.
Plant cells can be damaged or even destroyed by frost. Repeated freezing and thawing, or very rapid thawing can be particularly damaging to plants.
Once the temperature has fallen below freezing, a strong wind can make a frost more damaging. Cold winds remove moisture from evergreen foliage more quickly than it can be replenished by the roots; this can cause leaf browning particularly at the tips and margins.
Tender plants survive the winter better when they are planted in a sheltered sunny position. This is because new wood is ripened by the sun accumulating more carbohydrates during the growing season, making it more frost resistant.
Newly planted, young plants can be more susceptible to frost damage than fully established specimens.
Cold air naturally flows downwards on sloping ground, collecting at the lowest point or against a barrier, this is known as a ‘frost pocket’.