For Winemakers and Viticulturalists, Spring marks the shift from winter dormancy to reawakening in the vineyard. At this time, the groundwork for harvest is laid and important transitions occur, from inactivity to bud burst and flowering. As soil temperatures warm, sap begins coursing through vines.
This triggers a sequence of events which eventually results in the appearance of fruit on the vines.
Bud burst is the first stage of the vine’s annual cycle. New green growths appear, fed by water and stored nutrients. Small, fuzzy (or woolly) buds sprout.
As temperatures increase, tiny leaves, tendrils and miniature flower clusters burst through the bud, every day is a step towards the next vintage. Grape flowers typically arrive in late spring, roughly 40 to 80 days after bud break. Vines are self-fruitful, which means they self-pollinate without bees or wind. Each flower bears a single grape. This is a very delicate time that is easily impacted by the weather. The ideal conditions are from 15°C to 20°C without rain and little or no breeze. For the weather to stay like this consistently for two weeks would be a dream. Any rain or strong wind during this time can hamper flowering, disrupt pollination, and lower the potential yield.
Winemakers and Viticulturalists rejoice when the weather turns warm, but it also presents hazards for tender plants. Late-season frosts are particularly threatening. Vines are sensitive to injury from freezing temperatures once growth restarts. Lethal temperatures range from -3.5°C for swollen buds to -1.0°C during the leaf stage.
When the southerlies blow, and the temperature drops active measure to fight frosts come down to modifying temperatures in the vineyard. Wind machines, fans and even helicopters can stop colder air from settling around vine trunks by creating air currents and pulling warmer air down into the vineyard.
Nevertheless, for all Winemakers and Viticulturists, Spring remains a season of hope of great things to come.
Tim Adams
Winter dormancy in our Clutha Central Otago Vineyard
