The five phases of grapevine growth

The cultivation of grapevines in temperate climates is distinctly characterized by a succession of phases in its annual vegetative cycle. This cycle is a complex process crucial to viticulture, encompassing various stages from the mobilization of reserve substances to the period of dormancy. Each phase plays a vital role in the development and health of the vine, impacting the quality of grapes and, consequently, the wine produced. This article delves into these phases, providing insights into the intricate journey of grapevine cultivation.

1. Mobilization of Reserve Substances

The annual cycle begins with the mobilization of reserve substances, a critical phase for the nourishment of growing tissues, such as vegetative cones, and those yet to form. Before the development of elaborative organs (primarily leaves), the vine relies on its internal secretions, like enzymes, to transform reserve substances into soluble forms. This phase typically spans from just before the start of "weeping" (when sap begins to leak from the cuts made during pruning) to well after bud break.

2. Growth of Organs

This phase marks the growth of all organs, including roots, shoots, and leaves, and can be divided into two distinct periods. Initially, growth is fueled solely by the mobilized reserves. As the vine progresses, green organs, especially developed leaves, begin transforming raw sap into refined sap necessary for further development. The total growth phase extends from bud break to shortly before the grapes begin to change color (véraison).

3. Cessation of Lengthwise Development

Approaching véraison, the vine virtually stops growing in length. During this stage, the shoots and roots cease elongation. This phase marks a significant transition in the vine's development cycle, indicating the onset of fruit maturation.

4. Accumulation of Reserves

Post-véraison, the focus shifts to the accumulation of reserves, continuing until leaf fall. In this phase, the sap produced by the leaves is directed towards nourishing the newly formed organs, contributing to their enlargement. This sap is also deposited in the grape berries. The distribution of sap among the green organs, fruit, and perennial parts of the plant (such as branches, trunk, and roots) is a delicate balance. Excessive accumulation in any one area can detrimentally affect the others.

5. Dormancy

The final phase is the dormancy period, characterized by the plant's inactivity. It begins with the fall of the leaves and lasts until just before the recommencement of weeping. This phase is crucial for the vine's rest and preparation for the next cycle.

In contrast, grapevines in subtropical and tropical climates exhibit continuous growth without a dormancy period, due to consistently warm temperatures that prevent the vegetative zero (the temperature below which the vine stops growing). Here, grapevines behave as evergreens, with uninterrupted growth. Cultivation in these climates involves specific practices like regulated pruning and defoliation, creating a short rest period post-harvest. These techniques allow for the replication of the vegetative cycle up to two or three times a year.

The annual vegetative cycle of grapevines is a testament to the complexity and adaptability of this plant. Understanding these phases is crucial for viticulturists striving to optimize grape quality and vine health, whether in temperate, subtropical, or tropical climates.