Stag’s Leap Wine Cellars

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Stag’s Leap Wine Cellars

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Irrigation: Turning Water into Wine

As every home gardener knows, water is crucial to the success of any plant-growing endeavor. But in grape growing, the application of water – or irrigation – is the single most influential tool growers have to affect the desired outcome of a particular vintage. Too much water and the grapes will produce an insipid, vegetal wine; too little water and the wine will be overly tannic and astringent. It’s a fine line, and it’s one that Stag’s Leap Wine Cellars Vineyard Manager Kirk Grace walks every day.

“Irrigation is a tool to mimic ideal natural conditions in an environment subject to prolonged drying,” notes Kirk. “We look at it from the standpoint of the Mediterranean region, a climate similar to the Napa Valley. There you typically see maximum soil saturation at the end of a monsoon-like rainy season, and then a gradual drying of the soils as the growing season progresses and the grape clusters mature.”

However, in years when winter rains are unreliable or in times of prolonged drought, irrigation is essential for maintaining the proper moisture level in the soil. Of course the grower also has to have a reliable water source. At Stag’s Leap Wine Cellars we use reclaimed municipal water for irrigation under an agreement with the nearby town of Yountville. Using reclaimed water is one of the many ways we try to preserve natural resources. Also, drip irrigation, introduced in Napa Valley in the 1970’s, has vastly improved both the efficiency of water use and the precision with which it is applied to the soil.

“Drip irrigation gives our winery the ability to deliver water to the plant’s roots without watering the entire vineyard, as in the case of sprinkler irrigation,” says Kirk. “This results in a savings of total water applied and in a reduction of weed competition.” It also allows growers to adjust water application by vineyard blocks, or even to subdivide blocks into different watering regimes if desirable.

So how does a grower know when to irrigate? Although there are as many opinions about when and how much to irrigate as there are growers, generally speaking water is only applied during the growing season, between April and October (although very dry winters can be an exception). What makes it complex, according to Kirk, is that “while irrigation can help to react to current weather patterns, it is even more effective when we can anticipate dry and hot patterns and apply water proactively.” In other words, irrigation works best when the grower can accurately predict the weather.

Of course there are tools to help make the job a little bit easier. These include devices that measure soil water content, vine stress and evapotranspiration (the sum of evaporation and plant transpiration into the atmosphere). But as is often the case with grape growing, the human element is often the best. Kirk’s favorite method is simply inspecting the shoot tips of the vines. He uses a five point scale in which one represents rapid and luxuriant growth (favorable early in the season but not so favorable close to harvest) and five represents the drying of the shoot tip (unfavorable in both the early season and the late season).

It’s a fairly simple system that allows Kirk to get the information he needs from the vineyard itself, since “ultimately, the vine is the mirror of its own health.” With constant vigilance by Kirk and his vineyard crew, they’re able to determine whether irrigation and vine growth are in balance.

“In approximately 70 AD the writer and agriculturist Columella wrote about how to till, irrigate, and manage vineyards in dry conditions,” notes Kirk. “With knowledge passed down through generations, along with modern technologies like drip irrigation and weather forecasting, I’m confident that vineyards will continue to thrive well into the future.”