Natural factors make wine from particular regions unique, such regions known in the industry as “terroir”. These factors include various factors such as local climate, location of grapevines and soil composition and water drainage. Fruit bearing vines produces best fruits when climatic conditions are ideal such as lots of sunshine and cool nights without frost or hailstorms. In selecting a grape cultivar, one must consider the number of growing degree days, the length of the growing season and the frequency of exposure to low temperatures. The time required to mature grapes varies with location and climatic conditions and is dependent on the amount of heat experience by the vine. The frequency of very cold weather in winter will determine the survival of the vines.
The growing degree day (GDD) is used to calculate the amount of heat received in a region. It is calculated as the daily average temperature (max plus Min/2) minus the base temperature of 50 degrees F. below which grapes will not grow. Weather statics for climatic regions are provided by weather bureaus throughout the world.
Many variety types of grapes are grown in many regions of the world to produce grape juice, edible grapes, and wine of varying quality. Various grape vine varieties can resist to harsh climatic conditions where the winters are cold and the ground is covered with snow. Often, extra care is necessary to protect the vines during these cold winter climatic conditions. For example, rustic type grape vines are cultivated in regions where the degree days never exceed about 1200. In view of such cold climatic conditions the growers cannot grow quality wines, such as the vinifera variety grape vine which use the European technique of cultivation which consists in preserving the cordons on the vine cane with a few spuds during cold winter months. The European technique achieves a grape having a level of maturity which permits the production of a wine of superior quality as we find in Europe and the State of California.
Various methods have been used in an attempt to grow non-rustic vinifera type grape vines in unfavourable climatic regions. Such methods including, for example, cutting the cordons of the vine at the top of the cane every year as the wood cannot survive the cold winter months. The cane is thereafter covered by a thick layer of manure, earth, straw and a geo-textile fabric in order to protect the cane and the roots against temperature drops below minus 10 degrees Celsius. Such techniques pose a certain risk of losing the entire vine and are labour intensive in the fall and spring time period to cover and uncover the canes of the vines adding to cost. Also, there is the further risk against frost during spring time when unexpected cold weather can occur, and late fall when the grapes are still on the vines without protection against frost.
With reference to some published prior art, Chinese patent CN101563997 discloses a method of cultivation of grape vines offering protection against frost. It consists of covering the vines with earth and mulch and laying a plastic film over the vines with a sun-shading net disposed over the vines. In the spring. The covering is removed and the vines are unearthed and sprayed with a lime stone sulfur mixture. Such method, it is said permits temperature increasing and stabilizing, wind prevention and late frosting prevention. However, there is no form of controlling temperature as unregulated high temperature or low temperature can result in damage to the vines and poor crops.
US Patent Publication 2011/0247264, published on Oct. 13, 2011, discloses a trellis system for irrigation and frost prevention of agricultural plants. Heated water is sprayed and provides drip irrigation to an area surrounding the trellis system of plants to prevent the development of damaging frost. A protective net of fabric or plastic mesh is supported by the trellis and unfurled to partially or fully cover the plant to offer protection due to cold weather. When the temperature drops below 34 degrees F., a controller operates the hot water spraying system to prevent against frost damage.
U.S. Pat. No. 4,651,465 discloses another system for frost prevention of plants and especially citrus trees. A circulating water conduit is placed adjacent the tree trunk within a thermal barrier which is sealed at the top about the tree trunk and open at the bottom where the conduits enter the barrier. The conduit supplies heat to the space about the trunk and pours water onto the ground or sprays water over the tree to protect against freezing.