The beginning of this stage in the annual vegetative cycle of the vine. is about six to eight weeks after budding. The exact point in time depends on the year-specific temperature development, the temperature totals achieved at the respective location and the vine-specific growth under changing weather conditions. Constant warm temperatures with a good water supply accelerate the speed of shoot growth and thus the formation of the inflorescence (Latin: Inflorescence, also flowering, umbel, droplets or glow per country and region) on the third to seventh shoot node. Depending on the zonal climate, microclimate and solar radiation, flowering takes place from mid-May to late July in the northern hemisphere (in Central Europe, according to the old winemakers' rule, flowering begins on 24 June = St. John's Day, plus or minus eight days), in the southern hemisphere from November to mid-December. In contrast to many other flowering plants, the individual flowers of the vine are small, greenish-yellow and rather inconspicuous due to the absence of petals and show flowers. As the fruit ripens, the individual blossoms form the individual berries of the grape.
In the pre-blossom stage, the longitudinal axis of the inflorescence first stretches out, then the lateral branches with the still closely spaced, closed individual flowers spread out. With increasing development, the individual flowers detach from the flower cluster, swell and change colour to green-yellowish shortly before the actual start of flowering. Flowering begins when the first petals (perianthium), which have grown together to form a flower cap, detach from the flower base in dry, warm weather. In low humidity the flower caps are shed by means of an ingenious jumping mechanism, so that the honey-scented stigmas are exposed and the stamens can spread. At this time late frost would have an extremely negative effect.
The individual blossoms of the cultivated vine used in viticulture are hermaphroditic or bi-sexual in most grape varieties. This means that in a single flower they contain both the stamens with the male gametes in the pollen grains (= pollen) and the ovary with the female eggs and the stigma to be pollinated (see also in detail under flower bud). The stage of full flowering is reached when about half of the flower caps have been shed. However, the individual blooms on the flower heads do not flower simultaneously, but in a slightly delayed sequence, just as the individual flower heads of the vine do not start flowering simultaneously, but in a delayed sequence, depending on exposure (sunlight) and position on the fruit shoot.
The total flowering period is normally about eight days, but can last up to three weeks in bad, cold and wet weather. With increasing global warming or climate change, a trend towards earlier flowering dates with shorter flowering periods can be observed. The number and size of the buds as well as the number of individual flowers were already created one year earlier when the winter bud was formed (see under initiation). On a fruit shoot there are usually one to three (up to a maximum of five) inflorescences in the form of a so-called panicle (actually the term grape is not correct for the inflorescence of the vine). After flowering, pollination and fertilization, the ovary develops into a berry and the appearance into a grape. Each...