Can Rootstock Trials Save Napa Valley Cabernet Sauvignon?

Climate change is threatening Napa’s greatest asset. Andy Beckstoffer’s new research aims to preserve its future

rootstock clone planting
Rootstock clone planting. Photo by Lake County Wine Commission/Karen Pavone Photography.

Wildfires. Floods. Late-season cold snaps. Heat spikes at harvest. Few question that Northern California’s vineyards are experiencing the effects of climate change. In the Napa Valley, rising temperatures threaten to diminish the quality of the region’s iconic Cabernet Sauvignon—or perhaps eradicate it altogether.

Some Napa winemakers are planting experimental plots of grapes, such as Aglianico and Tempranillo, which may be more resilient to a hotter climate. But at least one winemaker refuses to accept that Cabernet’s days in Napa are numbered. 

According to Andy Beckstoffer, a change in farming—not variety—could solve the problem. “Cabernet Sauvignon is not going anywhere,” he says with stubborn conviction. 

A long-term study helmed by Beckstoffer Vineyards, the University of California, Davis, and Duarte Nursery aims to assess the effects of different rootstocks on different Cabernet Sauvignon clones in the Red Hills of Lake County. By studying 100 combinations of clones and rootstocks across 3,600 vines, Cabernet Sauvignon magnate Andy Beckstoffer hopes to ensure that the region’s emblematic grape is here to stay, despite the effects of climate change.

Climate Change’s Effects on Cabernet Sauvignon

In Napa, extreme weather events have made climate change particularly difficult to ignore. “The thing that’s really affecting us is the erratic nature of weather. Things are happening that have never happened before,” says Beckstoffer, citing as an example a May 2019 snowstorm in the Red Hills, which was followed by 100-degree temperatures a week later. 

Rising temperatures pose the greatest threat to Cabernet Sauvignon’s fate. In a 2018 symposium titled “Bordeaux in America: The Climate Disruption,” Greg Jones, a professor and climatologist at Linfield College in McMinnville, Oregon, stated that 15 of the past 20 growing seasons in California have been 3° to 5° F warmer than the 100-year average. Moreover, several recent harvests have started historically early; the 2015 harvest, which began on July 22, was one of the earliest on record in Napa Valley.

The region is also steadily moving up the Winkler Index of climatic classification. Napa Valley started on the cooler end of the scale at Region II, but it is now mostly a Region III or IV. As temperatures continue to rise, parts of the appellation will inevitably enter Region V, the warmest classification. According to the index, Cabernet Sauvignon can grow successfully in Regions II, III, and IV, but V is a likely tipping point. 

With cooler temperatures, Cabernet Sauvignon enjoys a long growing season, which results in fresh and elegant wines with balanced alcohol and acidity. But irregular climate events, such as frost, drought, and extreme heat spikes, can cause variability in both yield and quality. In 2015, a warm winter and spring led to early budbreak and bloom, but a sudden burst of colder temperatures in May caused uneven fruit set. These changes, combined with several years of drought, caused yields across California to drop 20 to 50 percent.

Heat spikes can cause grapes to sunburn or shrivel. In addition, sugars may skyrocket before such essential elements as acidity, structure, and flavor fully develop. The negative results of heat present winemakers with a difficult decision: Harvest the grapes earlier, before they are fully ripened, or let them hang and risk a wine that’s overripe and too alcoholic. In 2017, an extreme heat wave that pushed temperatures past 105 degrees Fahrenheit around Labor Day kicked ripening into high gear, forcing many winemakers to pick early. The only upside was that by October 8, when devastating fires rolled through, 90 percent of the grapes had been harvested. 

Dan Petroski, the winemaker for Larkmead Vineyards, says that the winery’s growing season has been tracking 10 days earlier than 15 years ago. “Ten days is a pretty big shift in seasonality that impacts color, flavor, and texture development of the grapes and the resulting wine,” he says. His data also shows that the region hasn’t only been experiencing warmer days, but also warmer nights. In 2019, nighttime temperatures were five percent above average. 

Left: Andy Beckstoffer, left, with David Beckstoffer. Right: Clint Nelson, left, and Andy Beckstoffer. Photos by Lake County Wine Commission/Karen Pavone Photography.

Seeking Solutions in Rootstock Selection 

The most significant effort to find a solution is the “Climate Smart Solutions for Cabernet Sauvignon Production” study, which is taking place at Amber Knoll Vineyard in the Red Hills. This trial is the brainchild of Clint Nelson, the director of vineyard operations for Beckstoffer Vineyards, and Kaan Kurtural, Ph.D., the lead researcher and a cooperative extension specialist in viticulture and enology at UC Davis and Oakville Experiment Station. Using planting material from Duarte Nursery, the team consulted various industry leaders to select the 10 clones and 10 rootstocks that will create about 100 possible rootstock-clone combinations—a meticulous process that took a year and a half.  

Over the past 50 years, numerous smaller trials have been conducted all over the world to study the impact of rootstock on various grape varieties and clones, but none of them have been done at this scale, says Nelson—and especially not with a focus on Cabernet Sauvignon clones. For example, in New York’s Hudson Valley, the Hudson Valley Wine and Grape Association partnered with Cornell University in 2017 to test four Cabernet Franc clones on three types of rootstock to discover the best rootstock for earlier fruit development. By contrast, in California, Beckstoffer’s team is looking for drought-resistant rootstock that can promote slower ripening in the face of dramatic heat spikes. 

The trial’s rootstocks were selected based on sustainability and resiliency goals and include some rootstocks that have just been released by the USDA and show strong promise of heat and drought resistance. The clones originated from Mediterranean-like climates across the world (including France, Argentina, Germany, and the United States). The team focused on quality, selecting clones known to deliver the best aromatics, mouthfeel, and color. 

“Grapevine phenology and plant development are strongly impacted by the scion and rootstock interaction,” Nelson explains, meaning that different rootstocks have varied interactions with the scion, which directly influences such factors as fruit set, vine vigor, ripening, yield, grape quality, and disease resistance. “This trial will hopefully identify combinations that avoid or tolerate spring and fall frost better, flower later in the year to avoid poor fruit set, adapt and rebound from extended drought, and maintain cluster and berry integrity through those drought events, all the while delivering the highest concentrations of quality components,” says Nelson. 

“The direct impact of rootstock on water relations and fruit quality has been proven,” he maintains, clarifying that rootstocks have the ability to directly affect both a vine’s water intake and its ability to handle stress, like a lack of water. This then indirectly impacts the fruit quality: the berry size, concentration of flavors, and dehydration. “This project will take those learnings and directly apply them at an unprecedented number of repetitions.”

The trial is expected to run for at least six to eight years. The vines have been planted in the Red Hills’ challenging, gravelly loam soil, and it will be another three years before the team can begin to crop the vines and start taking measurements with respect to drought tolerance, water-use efficiency, crop yield, and overall grape quality. With each forthcoming harvest, both the grapes and finished wine will be analyzed.

“We’ll see how they are, young and old. It’s a really long-term experiment because, in the end, you want to taste aged wines from those vines,” says Beckstoffer, who believes the results will help set Cabernet Sauvignon planting guidelines for vintners across many California regions. “The trial is in Lake County, but it’s for everywhere in Northern California. It’s for climate change, but really, wine quality. We’re trying to make these vineyards economically viable by producing better quality.”

Pictured here is Beckstoffer Vineyards’s Red Hills and research block. Photo courtesy of Beckstoffer Vineyards.

Napa Valley Without Cabernet Sauvignon?

California winemakers have been grappling with the effects of climate change and debating the future viability of viticulture for years. Randall Grahm, the founder of Bonny Doon Vineyard in Santa Cruz, California, made waves when he launched an experimental vineyard using money from a crowdfunding campaign. The project was designed to produce new grape cultivars better suited to California’s growing conditions. 

Petroski has also been especially vocal about the industry’s need to consider alternative grape varieties that will enable Napa Valley to evolve with climate change rather than crumble under it. He planted a research vineyard at Larkmead to test varieties that thrive in warmer climates, including Petite Sirah, Zinfandel, Tempranillo, and Syrah. Beth Novak Milliken, owner of Spottswoode Winery in St. Helena, California, has also begun experimenting with alternative varieties, like Alicante Bouschet, Charbono, and Valdiguié, and different rootstocks. Both wineries have built their reputations on producing premium Cabernet Sauvignon, but they don’t feel as though they can turn a blind eye to the hard data in front of them. 

Beckstoffer, on the other hand, is convinced that Cabernet Sauvignon is central to Napa’s identity as a wine region—and its commercial success. “If you’re trying to sell Tempranillo 10 years from now, you’re going to have a hell of a problem,” he says, adding that consumers will always look to Napa for Cabernet Sauvignon. Although it may indeed be possible to produce excellent Tempranillo in Napa, he explains, it will be incredibly difficult to sell. 

For Beckstoffer, the stakes are high when it comes to Cabernet Sauvignon. Arguably Napa Valley’s most prolific grape grower, Beckstoffer farms roughly 10,000 tons of high-end Cabernet Sauvignon grapes annually. He’s part of a growing cadre of vintners around the globe who are seeking solutions to combat climate change. Many are experimenting with shade cloth, irrigation, and cover crop. Some are purchasing land in historically cooler places. The difference here is that Beckstoffer’s efforts are laser-focused on preserving Napa Valley’s most lucrative asset. 

“I’m convinced we need to work within the current establishment of Cabernet Sauvignon,” he says. “It’s an important brand that’s grown all over the world. We have such a tremendous investment in it, so we’ve got to protect that investment. We’ve got to stick with what we do best and try to make it better.”


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Jess Lander is a writer based in Napa Valley, California, who covers wine, beer, food, and travel. Her work has appeared in Wine Enthusiast, Decanter, the San Francisco Chronicle, AFAR, and other publications.

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