Average air temperature below 10 degrees Celsius is too cold for the vine to grow, and this is typically after harvest in many of the northern as well as southern wine growing regions of the world. This marks the period when the leaf starts to fall off the vine and the phase continues through until Bud bursts.
Without leaves, the vine cannot photosynthesise. So until then, the vine will utilise the stored carbohydrates mostly within its roots and the trunks.
Places like Canada and New York state can be extremely cold and this can adversely impact the vines. Temperatures there can typically reach below -15 degrees Celsius.
One particular instance was the unusually cold winter of 1956 in south-west France, where severe cold weather had completely wiped out the grape variety Malbec.
Frost and cold temperatures can destroy cane and cordons first and eventually the other part of the vine, bringing up the painstaking need to replace the vineyard. Temperature below -25 degrees will destroy most Vitis vinifera.
In order to combat winter freeze, some regions choose hill side sites that can be 5 degrees Celsius warmer than the valley floor. Rivers and lakes near some wine regions can have a moderating influence on the vineyards, as water bodies tend to store heat during the winter. Cabernet Franc and Riesling are popular choices in cold climates because they are highly resistant to winter freeze.
Please note that on the other hand, unusually mild winters can cause the vines to not go through their full dormancy phase. This can result in over working and shorter life span for the plant, as vines also need to rest in order to prolong their life. Warmer winters can also result in two crops a year, which means more stress on the vine.
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