From the end of May, the clusters flower (the stamens and pistil appear).

This is an essential stage which, in large part, determines the potential harvest. If the weather is unfavourable, the flowers may not be fertilized: the pollen may be washed away by rain, which can sometimes cause a major shortfall in production. Some varietals are, however, more resistant than others.

he midway stage of flowering is important, because it helps calculate the theoretical date for the harvest. In Bordeaux area, for the Merlot variety, harvesting occurs around 110 days after the midway stage of flowering.