Cold Tolerance and Grapevine Phenology

2011 has been a really challenging year for growing grapes in the Northeast. In June, Wines and Vines had the following article about Eastern Winegrowers Face Weird Weather. In October, after harvest, there was an unseasonably early snowfall that covered a good portion of Connecticut. I thought that I would review my notes to see how cold affects the different stages of a growing grape vine(grape vine phenology).
There are three times during the year when cold can have devastating and potentially irrecoverable damage to a growing grapevine and they are:
1) During spring deacclimation
The young grapevine growing in the spring is especially susceptible to conditions that are even a few degrees below freezing as they deacclimate from winter dormancy.

2) During fall cold hardy acclimation
During the late summer and fall, the grape vines are preparing to go into dormancy by producing a layer called the periderm. The periderm provides cold hardiness to the vine by filling the inner living cells with sugars, proteins and amino acids. These compounds are the vine's cryoprotectant which enables it to withstand the colder temperatures of winter. The cryoprotectants bind up the water making it less available to form ice which can result in bursting the living grape vine cells!
3) During winter freeze and thaw conditions
The occurrence of severe freeze events in the winter is another way grape vines can become prone to damage to the point that they may not be able to survive. Mid-winter fluctuations that occur when cold temperatures are interrupted by a period of unseasonably warm temperatures and then becomes cold again can also lead to grape vine damage.

A really informative online article on cold and the grape vine can be found here:
Understanding and Preventing Freeze Damage in Vineyards
~ Workshop Proceedings ~
December 5-6, 2007 University of Missouri-Columbia