It has two distinct cycles: the winter cycle, when the vine is dormant or resting and it is pruned, and the vegetative cycle, as outlined here by Baron de Lestac.
At the end of February the vine reawakens. The sap circulates within the vine and when it reaches the canes' extremities it forms droplets where the vines have been pruned – these are the famous “tears” which indicate the start of the vegetative cycle.
From the end of March to mid-April the weather gets warmer and buds start to appear. Dotted along the canes, they have a downy, cotton-like protective cover and swell before bursting. This process is known as budbreak. The buds send out young shoots which will in turn become canes (if the grower allows this to happen). Vines are vulnerable at this stage, particularly to spring frost.
Leaves grow at the end of spring, opening and spreading little by little. They are crucial to the plant's overall development via photosynthesis (the process by which it produces the necessary organic compounds) and as such could be considered as vital organs.
Clusters of small white flowers start to appear at the first signs of summer, encouraged by the sunshine and warmer temperatures. These flowers will develop over the next two weeks. Clusters can be seen, each bearing 100 – 200 flowers. A lesser-known fact is that most varieties of vitis vinifera vines (ie. the species that is most commonly planted today) have hermaphrodite flowers which self-pollinate. During this phase, weather conditions can cause the flowers to shrivel and not be pollinated.
In early June, the pollinated flowers wither and fall, revealing the very first signs of grape berries. Fruit set is the term used to describe the stage when the fruit is fully formed. The berries are small, hard and bright green. They are also of a similar size, as long as flowering and fertilisation have gone smoothly; if this is not the case, the bunches may contain berries that differ greatly in size (this is known as millerandage or shot berries).
From mid-July onwards the vines are fascinating to observe. The grapes which have been green until now begin to change colour. However, this does not happen at the same rate for all berries within a cluster, creating colourful patterns in the vineyards. The sugar content of the pulp gradually increases but it is still very bitter. The growth phase comes to an end and maturing begins.
From August to early October the berries increase in size and complexity. The sugar content is stocked and is no longer used purely for growth, thus acidity levels start to fall. The grapes are considered to be at optimum ripeness and ready to be harvested when sugar and acidity levels are in balance.
Harvest usually happens between September and October. However, as grape vines are subject to climate and weather conditions, these dates can vary from one year to another. Grapes are picked by hand or machine, and sorted in the vineyard or at the winery, the most important point being to harvest only the very best fruit.