I borrowed this drawing from Washington State University. You can Click this link if you’d like to learn a bit more about grapevine buds as relates to frost damage.
The options available to limit the damage frost can cause to grapevines are either passive or active.
I use passive management in that I have planted my vineyard on a slope that allows cold air to flow down the hill. I keep the inter row grass mown short to encourage this cold air flowing down the hill and exiting the vineyard.
I mulch under vine to minimise grasses and to improve earthworm activity. But this a bit of a compromise when it comes to frost because the best result for frost is to keep the strip under vine bare earth as this absorbs more of the sun’s heat and releases it at night minimizing frost risk. I’ve often thought that this would be a good place for ground up old car tyres as the black would capture more of the sun’s energy whilst limiting the growth of weeds… perhaps some enthusiastic graduate student will pick up the idea for their doctorate thesis someday.
Active frost management utilizes giant wind machines (sometimes helicopters) or sprinklers.
The principle involved in sprinklers is that it requires energy to convert water to ice and as this ice builds up on the vines it insulates the leaf cells from the energy required to the form killing ice crystals within the plant cells.
Wind machines rely on mixing the warmer air above the vineyard with the colder air on the ground. When frost is accompanied by high winds this advantage is lost as the warm air above is already mixed with the cold air on the ground.
There are also various proprietary products available to spray on vines prior to a frost event that can offer a degree of frost protection, but I don’t have much experience with these.
On a calm night my passive frost managed vineyard can tolerate temperatures as low as -2 degrees. However, the lower half of the vineyard suffered damage a few years ago at -0.5 degrees accompanied by a north wind. It is unusual to have frost with north wind this time of year; our cold weather is normally associated with Southerlies. The frost from my vineyard drains down the valley to the north so the north wind reversed this drainage and blew it back up to my vineyard with disappointing consequences.