Most California vineyards require irrigation. Irrigation can be used as a tool to increase wine quality through judicious application of water. Conversely, there is the potential to decrease quality. Too much water in the grapes can result in diluted flavor. More importantly, with poorly timed irrigation the vines may not be physiologically tripped into the ripening mode, and as the season draws to an end, the plants may continue to bear healthy leaves and produce sugar, but ‘forget’ to produce the all important flavor components.
Our Vineyard, Morningside, is particularly tricky because it wraps around a hill with very thin soil at the top and a wet swail in the middle. As a result, we must carefully monitor our irrigation and the plants to insure they are receiving the right amount of water.
A major threat to vineyards in Napa Valley is heat waves. Late season heat, when the fruit is at its most fragile stage just prior to harvest, can lead to dehydration and a large percentage of grapes can be turned into raisins. These conditions often occur when the day-length is longer, and on hot days the sun has more time to beat down on the grapes.
One option is to plant vines on drought-resistant rootstocks, such as St George, which is used in our Morningside Vineyard. This rootstock sends down deep roots to obtain any available water from the subsoil.
To increase the quality of our wines we want to push the envelope of ripeness. We want the vines to produce more flavor compounds to make wines of greater richness. The lack of water in summer and fall limit the amount of growth that the plants can achieve, the amount of fruit they produce, and most importantly, the ability of the fruit to reach full ripeness. By carefully managing irrigation of the vines, we can maintain healthy plants and obtain more intensely flavored grapes that produce premium wines.
One of the methods we use to influence and improve grape quality is the practice of regulated deficit irrigation. Deficit irrigation occurs when the vine receives less water than it is capable of utilizing, thereby inducing a stress on the grapevine. There are three main goals of regulated deficit irrigation: 1. Stop shoot growth; 2. Induce and control stress and 3. Maximize grape flavors. The first goal is to stop shoot growth once the desired canopy size is achieved. Overly vigorous canopies can contribute to undesirable vegetal characteristics in the wine. Once shoot growth is stopped, a mild or moderate stress is induced in the vines by regulating the amount of water the vines receive. Our goal is to reach a mild stress level at Verasion and maintain that level until harvest. By judicious application of water we can improve the quality of the grapes and the wine.
Carefully monitoring and regulating the amount of irrigation the vines receive can obtain the desired level of stress. To monitor the water status of the vines we use a device called a “pressure bomb”. The pressure bomb reads the water content of the vines and enables us to determine what level of stress the vine is under from unstressed to mildly, moderately, highly or extremely stressed. By knowing exactly how much stress the vine is under, irrigation can be managed to optimize fruit quality. To see a video of our irrigation manager, click paly below.