2.8.2.b How are vines affected by frost?

Impact of frost at different times of the year

• In the spring: frost damage occurs more frequently but is less of a threat to the vines' survival. Vines are sensitive as soon as the young leaves emerge, which have a high water content. In high humidity, the young shoots can freeze at -2 to -3°C whereas in drier situations (humidity <60%), they can resist up to -4 or -5°C. These frosts never lead to the death of the vine but they can destroy the harvest.

• In the autumn: early frosts, before leaf fall, are particularly damaging to young vines, which often have a longer growth cycle. Herbaceous organs are generally affected when the temperature drops below -2.5°C

• In the winter: if the temperature falls below -15°C, the buds, the branches and trunk can be affected. It is possible for such frosts to kill a vine.

Mechanisms of action

The cells' intermembrane spaces are less rich in minerals and therefore freeze more easily. The minerals act as shield molecules that prevent ice formation by inserting themselves between the water molecules, which are then more widely spaced and have more difficulty freezing. This phenomenon lowers the freezing point of water. Due to the osmotic imbalance between the cell and the outside, the cell exudes water (exosmosis: the phenomenon of water flow from the inside of the cell to the outside to rebalance the osmotic potentials of the cytosol and apoplasmic water) and becomes dehydrated. This leads to the cells breaking down.