Chapter 1

Annual Growth Cycle of the Grapevine

Flower Cluster Initiation

As the new primary shoot develops, flower clusters form opposite a leaf. Where a flower cluster does not develop, a tendril may grow opposite the leaf. A fruitful shoot usually produces one to three flower clusters (inflorescences) depending on the variety and growing conditions of the previous season under which the dormant bud (that produced the primary shoot) developed. Many grape species, including most varieties of Vitis vinifera, form only two flower clusters per shoot. French-American hybrids as a group tend to flower prolifically with four or more clusters per shoot. Location of these clusters on the shoot also is specific. Flower clusters typically develop at the third to sixth nodes from the base of the shoot with a cluster containing several too many hundreds of individual flowers. Flowering normally occurs within six to eight weeks of bud break, beginning on the uppermost shoots. The precise timing varies with weather conditions and variety characteristics. For individual clusters, flowering starts from the base of the inflorescence. The bloom period usually lasts from 1 to 3 weeks.

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