Late Spring / Early Summer is a time of great anticipation in the Vineyards as we await to see how much fruit is going to successfully set following flowering. This is one of the earliest indications of the likely size of Vintage.
Several key factors play their part here, most importantly air temperature, soil temperature, soil moisture levels, vine nutrition, and vine canopy condition.
Air temperature in the range of 15ºC to 30ºC is ideal. Extended cold periods do not allow the pollen to develop properly, and high temperatures cause pollen to dry and become unviable.
Cold soil temperatures and high soil moisture levels result in flowering over an extended period with usually poor set. High soil temperatures and low soil moisture levels result in poor photosynthesis in vine leaves also resulting in poor set.
Very high nutrient levels particularly nitrogen, and low level of trace nutrients particularly zinc are common causes of poor fruit set.
Excessive canopy growth results in shading of the flower clusters within the canopy reducing flowering and set, whilst under-developed canopies result in overly exposed flower clusters also reducing flowering and fruit set.
Overall, a quite complex array of interactions are at play here. Thankfully early indications are showing good fruit set – only two thirds of the growing season left now to determine what Vintage will be like!