Vine leaves its winter rest according to a fairly well established « protocol » that already starts in winter. Everything begins with so called « tears », drops of water that appear on pruning wounds. They indicate that the roots of the vine have completed their winter sleep and become active again, pushing water up towards the wood. The number of weeks that may pass between appearance of the first tears and bud burst varies, because the internal clock of the plant depends on soil temperature and length of days. When all the external conditions are favorable, the vine wakes up and starts the new vintage.
All varieties are evolving at their own pace. Beyond their sensitivity to external factors, they also have a kind of internal clock, included in their genetic code. Depending on that natural “biorhythm”, we distinguish between early and and late ripening varieties. What matters to us in the end it is to pick the grapes from each vine at their optimum maturity to create our wines. That’s why it’s useful to know the ripening period of varieties we plant. Thus, based on comparison with the Chasselas variety as a standard, grapes have been classified as first-, second-, and third-phase varieties, according to whether they ripen at the same time, 12 days later or 24 to 30 days laters than Chasselas grapes if grown under the same conditions. This classification is also called Classification Pulliat, according to a French ampelographist of the XIXth century.
Short cycle varieties are traditionally established in cool wine regions and grape varieties of longer cycles in warmer regions. Of course, the short-cycle varieties show some tolerance to a warmer climate, as there is some good Chardonnay and or Cabernet to be found in warm wine regions, and Viognier, a very aromatic white grape from Condrieu in the northern Rhône Valley, since several years is extending into the Mediterranean vineyards. The installation of third-phase varieties in cold regions, however, is more difficult and sometimes impossible, because their grapes simply do not arrive at maturity.
But let’s look at what happens at the time of bud burst. The buds open in days and unfold the first leaves. But that’s not all. They also contain the tiny grapes, that will be picked five or six months later. In other words, the buds that are bursting at the moment around the vineyards of the northern hemisphere, already contain the harvest of this year. That is why winemakers are particularly concerned by frost or hail in spring. While these two phenomena rarely put the plants in danger, they may still seriously affect the harvest of the year.