Understanding the vines and what they need
The stage for the 2022 vintage was set in autumn 2021.
Wet conditions in late summer and autumn enhanced disease pressure. In 2021 Grenache, the vine that stays green the longest, lost its leaves in March rather than late May.
The photosynthetic work done after the grapes are picked in late March or April is required to restore carbohydrate levels in the shoots, arms, trunk, and roots that are heavily depleted in ripening the crop. The greater the leaf area in the following November, when flowering occurs, the larger will be the bunches and the number of berries that set seeds. If a berry doesn’t set seeds, it fails to grow. The rate at which leaves were developed in the growing season leading up to vintage 2022 was slowed by cool windy conditions and the poor carbohydrate status of the vines following vintage 2021.
If one can increase the leaf area or give the leaves better access to sunlight then more roots, leaves, shoots, and fruit is produced. Similarly, in a pasture system, growing a mixture of plants that have short and tall-growing habits can increase the working leaf area and rooting depth, thereby increasing the carbon content in the soil which feeds the microflora that has a symbiotic relationship with the plant, exchanging carbohydrate for plant nutrients not otherwise available to the roots.
Professor Gordon Howell of Michigan University in the USA examined the grapevine as an input/output system. Using potted vines, Howell manipulated water, sunlight, pruning and cropping levels in a controlled fashion. To measure performance, he harvested the whole plant measuring the weight of fruit, shoots, trunk and roots.
Inspired by the logical, systematic work of Professor Howell, I decided many years ago to harvest the leaves on a single vine on the same day that the fruit was harvested. I wanted to know the leaf area to fruit ratio. In the following year, that vine turned into a midget. This was an important lesson learned.
Next year should see a return to crop levels closer to normal because a dry finish to the season enabled the vines to work harder for longer.
The grapevine is the richest producer of carbohydrates in the pantheon of fruit producers, but its performance depends on the work of other plants. Many decisions of the vigneron (grape cultivator) bear upon the health of this system.
Carbohydrate is derived from the sugars produced in the leaves as they assimilate carbon dioxide from the air. The enhanced amount of CO2 in the air enables the vine to survive with less water, and the planet is greening accordingly. Leguminous plants fix nitrogen from the air. Air is 80 per cent nitrogen but unless it can enter the soil via passages made by decaying roots it cannot be accessed by plants.
So, a vigneron needs to make sure that they maximise the leaf area of the grasses that grow in winter when the vine is dormant. Running sheep in the vineyard is contraindicated as is the use of herbicides to prevent weed growth under the vine.
If one can understand the input-output dynamics and act accordingly, its better than simply following the current fashion.