The grape starts its annual growth cycle in the spring with bud break. In the Northern Hemisphere, this stage begins around March while in the Southern Hemisphere it begins around September when daily temperatures begin to surpass 10 °C (50 °F).
Flower Cluster Initiation
As the vine grows, the maximum yield is set by the production of flower buds. Warm, sunny weather promotes grapevine growth. By the time the shoots are 4 to 8 inches long, small flower clusters can be seen. The clusters will be clearly visible by the time the shoots are 10 to 16 inches long. They can be thinned at this time so the sugars produced by the leaves at later stages are shared among fewer grapes and those grapes grow larger and sweeter.