Winter is a wonderful season. Right in the middle of the year, it allows time to contemplate how far we have come and to reconsider and plan for the six months ahead. And without the lush green of spring and summer and even without the bronzes of autumn, winter gives a new perspective – each year I appreciate the beauty of the historic Cape Dutch buildings presenting themselves through the bare branches.
The Cape Winelands is known for its age-old oak trees providing lush shade during the warm summer and the prettiest show of colours during autumn months. But why are the trees left to face winter with their bare arms?
Leaves are green because of the chlorophyll they contain. The plant uses the chlorophyll for photosynthesis through which sunlight, water and carbon dioxide are used to form oxygen and glucose used for growth. During autumn, when days are shorter and the sun milder, less chlorophyll is produced and the green of the leaves become less intense. The yellow, orange and red that are always present in the leave become more obvious in winter when the green fades away.
So why do the leaves eventually fall off?
At the end of each leaf is a special layer of cells responsible for transporting water between the leaf and plant during the warmer months. When the colder season arrives, these cells turn into a cork-type substance that halters the transport between leaf and tree and eventually causes leaves to fall off.
While winter is an all-important time of rest for most plants, the changes happening during the cold months are very important – especially for the vine!
As temperatures fall and days get shorter, interesting physiological changes take place in the vine enabling it to survive the cold. The leaves change from green to yellow to brown and then start falling off. (Interestingly enough, although the bright purple and red leaves are lovely to look at and make for exceptionally beautiful pictures, they are a sign of stress in the plant.)
Now the vine’s metabolism slows down. No energy is produced through photosynthesis and the plant survives on the stored energy of the growing season. Having enough stored energy is very important as it will be used in spring to restart the growth cycle.
No water is absorbed during winter and cell water is moved to an inter-cellular area to protect the plant from damage should this water freeze in winter. With carbohydrates stored in the lower parts of the vine and as there are no leaves in the way, winter is also the ideal time for pruning.
A cold and wet winter is important for the quality of the harvest. While winter conditions in cooler climates can injure grapes because of too low temperatures, our Southern Hemisphere winters need to cool down sufficiently to allow vines to enter their resting phase. Ideal conditions include sufficient cold units and water. In dryer climates such as ours, groundwater as well as reservoir volumes for irrigation should be replenished.
Plenty of reason to enjoy the cold and the rain! The reward is in that beautiful glass of wine you are enjoying in front of the fire place.