Flowering of some varieties of grapes begins at a temperature of 16 -18 ° C, although the most favorable temperature for this crucial period is 25-30oC. If the grapes grow on well-lighted place, its flowering period may occur earlier, even at not so favorable temperature conditions. It is noticed that the same grape variety can bloom at different times, being in the same climate zone, but under different lighting conditions. Unfortunately, when the temperature drops below 15 ° C, during flowering, many varieties of grapes are not fertilized, so it is important to protect the plant from spring cold snaps.
The grapes begin to bloom in the early morning, at sunrise, about six hours. This continues until eleven in the morning. In these watches there is a mass flowering vine in the rest of the time, reveals only some belated flowers. Morning hours is most beneficial due to the humidity, because the first time is very important to the stigma of the flower vine did not dry up. Approximately 24 hours after the start of flowering in case of successful fertilization, the stigma of the flower begins to dry and change color from light yellow to brown.
For heterosexual grapes of particularly dangerous weather conditions during the flowering period are the rainfall, as the female flowers aren't fertilized. The fact that the rain washes away the pollen, and it simply does not have time to grow into the necessary for full fertilization amount. Even under favorable conditions, fertilized only half of the flowers, this is one of the biological features of plants of grapes. In order to protect themselves from the adverse effects of bad weather, you should not grow grapes without shelter in areas where in the spring of the year there are frequent rains.
During flowering it is not recommended to irrigate the vineyard. It may have a negative impact on the future harvest. All in a sharp increase of air humidity during irrigation. This is not a natural process, and therefore, can significantly reduce the number of fertilized flowers. If the vineyard is small, then increase the next harvest it is recommended to use artificial pollination. On large areas is difficult, which is why the grape harvest depends on weather conditions, and from year to year, its volume can change. The flowering period of the grapes is from seven to twenty days depending on the climatic characteristics of the terrain and grade.
During flowering the vineyard is the most vulnerable to pests and diseases.
If during flowering of grapes is observed lowering the temperature below 15 ° C, it is necessary to resort to methods of artificial pollination, otherwise you can remain without a crop.