Depending on temperatures, 40–80 days after bud break the process of flowering begins with small flower clusters appearing on the tips of the young shoots looking like buttons. Flowering occurs when average daily temperatures stay between 59–68 °F which in Eastern WA is generally around May. A few weeks after the initial clusters appear, the flowers start to grow in size with individual flowers becoming observable. It is during this stage of flowering that the pollination and fertilization of the grapevine takes place with the resulting product being a grape berry, containing 1-4 seeds.
The stage of fruit set follows flowering almost immediately, when the fertilized flower begins to develop a seed and grape berry to protect the seed. This stage is very critical for wine production since it determines the potential crop yield. Not every flower on the vine gets fertilized, with the unfertilized flowers eventually falling off the vine.