It’s wintertime in Wine Country and the vines are undergoing their crucial transformation into dormancy. As the temperature drops and the days get shorter, a remarkable physiological change occurs within the vine that allows it to endure the cold winter months.
The vine leaves will turn from green to yellow to brown before falling in a process called senescence. Bright colored leaves of red and orange may be pretty to look at and to photograph, but are generally a sign of stress and disease, two things not desired by the vineyard manager.
By now, the vine has discontinued its metabolic process and has stopped producing energy through photosynthesis. The plant will rely exclusively on the stored energy it has gathered throughout the growing season in its roots, trunk and branches. This energy will be vital to jump-start the conversion from dormancy to bud break when spring arrives.
As the vines carry on their preparation for the cold temperatures, chemical changes will help protect the living cells inside. Water inside the plant’s cell tissue can freeze during the winter, causing the cells to burst and thus damaging the vine; during dormancy, the vine develops a remarkable natural defense to this threat.
First, the vine stops the uptake and absorption of water from the root system, and second, it transfers water out of the plant cells and into the inter-cellular area where it can safely freeze without causing damage. Truly amazing!
With our expected arrival of the winter rains the cover crops are starting to grow quickly. Cover crops are used for a broad variety of reasons, including providing a habitat for beneficial predatory insects that are needed to help sustain an environment of balance.
Planting and establishing cover crops may also be used to prevent and control erosion on hillside slopes; they may even be mowed and mulched to be used as a source of nitrogen to enrich the soil. If a particular vineyard site needs to be de-vigorized, a cover crop may be planted to compete with the vine for water. The most common and easily identifiable cover crop is mustard. We will also seasonally rotate cover crops using clover, vetch and fava beans. Chianti anyone?