Breaking Buds

Breaking Buds

The following text and photos are contributed by Flying Goat Cellars Ambassador Faye Walker, Ph.D.:  

Vineyards as a Vector

While we all know that grapevines are necessary for making wine, it's easy to take the involvement of these plants for granted.  In the presence of light, the stems and leaves transform water and carbon dioxide into fruits and flowers.  It's the grapevines that do all the work in the vineyard:  year after year, they take what they need (not necessarily what they want) from the soil and the weather to bring us the flavors in a finished bottle of wine. Right now, the vineyards that we source from are well into bud break. How are their contributions looking this season?  Read on to see how the factors of this past season are contributing to springtime growth.

Grapevine Structure and Function
The anatomy and physiology of grapevine structure and function reveals an intricate, complex organism. Like other green plants, grapevines manufacture their own food by converting sunlight into chemical energy through the process of photosynthesis. In chemical terms, the sun's energy is used to split water molecules into molecular oxygen and hydrogen. Those hydrogen atoms go on to donate electrons in a pathway of reactions that will provide plants with carbohydrates.
Photosynthesis takes place in the leaves of grapevines. Highly specialized organelles, chloroplasts, are adapted to carry out this function. Leaves provide a large area to draw in sunlight; they contain an abundance of cells with chloroplasts; their stomata uptake carbon dioxide (a main contributor in the production of carbohydrates); and their tissues export food out of the leaf. As for the food itself, the products of photosynthesis are mainly sucrose and starches. Vines store their various forms of food energy in reserve until they are needed.  Somewhere between March and April, the time comes to use that energy to build plant cells.


Bud Break
In spring, grapevines experience a burst of fresh growth. Warming of the soil temperature causes the vines to awaken and produce new growth. The carbohydrates that were stored in the vines are used as structural materials to build plant cells.  These vines will grow to eventually convert sunlight, carbon dioxide, and a mix of mineral nutrients (nitrogen, phosphorus, sulfur, iron, and others) taken up by the roots into other compounds that will be used throughout the plant.

The process by which buds form flower clusters and go into bloom is influenced by a number of environmental factors.  The amount of sunlight, fluctuations in temperature, differences in growing conditions, or seasonal variation can significantly affect the outcome of photosynthesis. The budding (process of bud break) that we are seeing across the central coast actually began around Memorial Day in 2023. The berries that develop in this year's crop will be the result of the weather throughout two growing seasons. Moreover, the upcoming harvest will be the first in a long while to be free of drought-induced water stress.


Balanced Vines
Grapevines will ultimately reflect their environment. As such, water availability is a key component of the growth cycle. The physiological reaction of vines to water access will affect the growth and development of the shoots, leaves and fruit depending on the season. Vines that are overly irrigated and vigorous can spiral into a vegetative state, leading to reduced fruit set and lower yields. On the other hand, vines that are overly stressed from deficits can experience reduced bud break and poor shoot development from stunted growth.

What happens to grapevines during drought years? Excess water stress causes a physiological response that reduces photosynthesis and cell division. In the worst case, this can cause cell desiccation and death. While we don't yet know how these vines will bounce back from their subjection to drought conditions, we can say that good irrigation practices account for both drought management and over irrigation. Simply put, reactive and proactive farming practices can be one of the most important tools in ensuring wine quality


To The Future
Throughout April and May, we can expect the bud break to turn into vegetative growth. Flowers will form; berry clusters will develop; grapes will ripen; and harvest will begin when the fruit has reached its optimum. At the end of the line, the major point is this: healthy soil produces a healthy vine, a healthy vine produces healthy fruit and healthy fruit produces healthy wines.


Sources and Further Reading:
Patterson, T. and Buechsenstein, J.  Wine and Place:  A Terroir Reader.  University of California Press:  2018.
Wikipedia.  "Annual Growth Cycle of Grapevines."
Wikipedia.  "Chloroplast."
Wikipedia.  "Water Splitting."

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