California’s Trellising Systems Adapt with the Times
While wine grape varieties in California often change to reflect what is in or out of vogue with winemakers and consumers, the types and styles of wines that are made are also affected by trellising choices in the vineyard, which can significantly impact the health and vigor of the grapes.
Trellising systems have evolved to encompass an increased understanding of viticulture and winemaking in the state, considering changing climatic conditions, style preferences, economic pressures, and choices between mechanized and hands-on labor.
In California’s warm climate, how grapevines have been trellised has long impacted the flavor and intensity of the resulting wines. Having experimented with several different types of trellising systems across a variety of regions over multiple decades, California grapegrowers in many areas are reconsidering the systems they use in their vineyards as changes in climate and style become increasingly relevant.
John McCarthy, the director of vineyard operations at Far Niente Winery, in Napa Valley, is one of them.
“Over the past few years, we’ve made significant improvements in key vineyards, like our new Grand Sky site, in Carneros, and the historic Martin Stelling Vineyard, in Oakville,” he says. “Trellising can have a big impact on overall fruit quality. In both sites, we’ve moved to a horizontally divided system, creating two planes of canopy. This allows more sunlight to penetrate the canopy and allows more even exposure to the sun through dappled light.”
McCarthy sees these enhancements, along with changes to rootstock and row orientation, leading to higher-quality wines. This trellising change, he believes, also decreases fruit congestion, improves photosynthesis, regulates temperatures, and promotes better phenolic development. He also thinks it mitigates heat risk, with the sun hitting the top of the canopy at the hottest part of the day, providing a natural shade for the berries.
“It helps protect against climate change through shading and optimal sun exposure,” McCarthy adds.
The History of Trellising Systems in California
With a history of grapegrowing dating back to the time of the Spanish missions, by the time of statehood, in 1850, California had just a few hundred acres of wine grapes, most of which were sold for a high price to wine businesses in San Francisco and Los Angeles. The money that flowed from those grape sales led to more investment in planting vineyards, with planted grapes reaching a total of 56,000 acres by 1880.
Then, Pierce’s disease struck, and most of what was planted, especially in Southern California, was pulled out, with production moving largely to the center and north of the state. By 1910, there were 350,000 acres, but supply eventually outpaced demand and prices for grapes fell.
Throughout most of this time, grapevines were head-trained without wires or stakes, essentially what still exists in old vine vineyards where there’s no trellis system. Instead, in head-trained vines (also known as gobelet), spurs of the vines were left to grow in a variety of directions, with dramatic differences in how each of the clusters was shaded.
Gobelet was a method borrowed from fruit trees, as written about by Edward J. Wickson in The California Fruits and How to Grow Them, published in the 1880s.
For grapes, the gobelet method can result in variability in ripening and is labor-intensive in terms of pruning and harvesting. Head-trained vines are often dry-farmed as well, forcing roots to dig deep into the soil to find moisture without the help of irrigation.
Once Prohibition hit California, many of these head-trained vineyards were pulled out or abandoned. Pockets of them remain, and they are often revered for their historic significance and longevity, sustained by winemakers searching for old vines.
After Prohibition, new plantings resumed throughout California, though slowly at first. According to UC Davis, between 1920 and 1973, acreage devoted to wine grapes ranged from 100,000 to 200,000 acres across the state, an area smaller than the acreage devoted to raisin grapes.
That shifted between 1973 and 1977, with wine grape acreage doubling in four years to reach 318,000 acres, finally exceeding raisin grapes, especially in the Central Coast and San Joaquin Valley, with most of the vines planted for fine red table wines. By 1978, 83% of California wine was classified as table wine.
With a total of 330 wineries by 1975, California wine acreage and production boomed over the ensuing decades: there are now 6,200 wineries and 5,900 grapegrowers in the state.
Much of the growth in California’s wine grapes occurred during an era of large-scale replanting in the late 1980s and 1990s, after phylloxera decimated many vineyards. Phylloxera is an insect related to aphids that feeds on the roots and leaves of grapevines, cutting off water and nutrients. Phylloxera is native to North America, and there is no cure for it. Affected vines must be pulled out and new ones planted on phylloxera-resistant rootstock.
Within the context of America’s booming consumer interest in wine, California vineyard owners were able to not only consider new varieties—more Cabernet Sauvignon and Chardonnay, for example—but also rethink trellising.
The era’s bigger-is-better ideology prevailed in many areas, with the belief that more exposure to sunlight and heat would produce more flavorful, darker-hued and more robust grapes and, thus, more flavorful, darker, and more robust wines.
Increasing sun exposure on the vines was also a way to maximize ripeness in the grapes and diminish an overt presence of pyrazines, whose herbal, vegetal flavors were drifting out of favor with most American winemakers and wine drinkers.
The winemaker Zelma Long was the head of Simi Winery, in Sonoma County, throughout most of the 1980s, overseeing both winery and vineyard development. In an oral history about that time, she noted: “With Cabernet in particular, the vineyard issues were ripe fruit flavors, i.e., moving away from the herbaceous, vegetative flavors that we saw more frequently in the early seventies and eighties, to the blackberry, black cherry, cassis, very ripe fruit flavors of Cabernet – and ripe tannins. . . . The Cabernet grapevine does have the ability under poor circumstances to produce very astringent tannins, so the goal was to display the fruit and balance the vine in such a way that by the time the grapes were ready to harvest, the tannins were ripe.”
The prevailing trellising system in this era became known as vertical shoot positioning (VSP). VSP trellises allowed more rows to fit per unit of land than previous sprawls, which was of interest to any growers looking to maximize the economic viability and sustainability of their acreage.
First used in cooler areas of Germany, France, and New Zealand, VSP was also effective in warding off fungal diseases and reducing mildew pressures. In California, however, it was widely used in warmer areas, too, such as Napa Valley. This indeed led to more even ripening and, in many cases, to what many considered a period of bigger, bolder wines.
In 1985, there were 320,782 acres of wine grapes, according to the California Department of Food and Agriculture’s California Grape Acreage Report. The acreage steadily rose from there, and, at its height, in 2013, California was growing 469,790 acres of wine grapes. The latest figures (2022) show wine grape acreage at 449,223.
Trellising Systems 101
Throughout these periods of growth, there were multiple trellis and training systems and canopy management practices that were used, as detailed in Wine Grape Varieties in California, published in 2003 by the University of California Agriculture and Natural Resources.
In the book’s chapter titled “Trellis Selection and Canopy Management,” the author Nick K. Dokoozlian notes, “Over the past two decades, advancements in vineyard design, trellis and training systems, and canopy management practices have dramatically improved wine grape productivity and fruit quality in California. Prior to this period, a standard vineyard design and trellis system was used throughout the state. Little attention was paid to site-specific factors influencing vine vigor such as climate, growing region, soil type, and rootstock. Now significant effort is made to match vineyard design and trellis system to the site-specific factors that influence potential vine growth.”
Trellising begins with vine trellising. As Jonathan Swinchatt and David G. Howell note in The Winemaker’s Dance: Exploring Terroir in the Napa Valley, “A naturally growing grapevine does not look like the vines you see in Napa. Left to its own devices, the vine’s strongest shoots will extend themselves to the detriment of others—the plant will become a true vine, climbing and clinging to the surrounding growth, reaching farther each year.”
A vine would also bear hundreds of clusters with a small number of berries, allocating just enough energy to ripen those berries to a degree of sweetness that would attract birds and animals, but that amount of sweetness is not ideal for wine grapes. The right amount of ripeness involves the grower, who must direct the plant’s energy to the berries.
Vines in many vineyards across California are trained vertically, with wires that hold the shoots upright. Fruit clusters form at the base of the shoots, hanging below the canes, exposed to the sun.
As Swinchatt and Howell explain in The Winemaker’s Dance, “Rising from these horizontal limbs are dark stubs with canes growing up through the containing wires, forming a linear, vertical wall of green. These are cordon-trained vines, with permanent canes attached to the lower wires, some trained bilaterally with cordons in both directions from the vine stem, others with a single cordon.”
Cane-pruned vines, on the other hand, are less orderly, without permanent growth other than the main stem. The shoots are pruned back to one or two canes every year, with the buds on these canes held vertically by a two-wire trellis. Cane-pruned vines typically require more attention than cordons, with every vine assessed for health and strength for the next year, since only one or two will be kept.
Others opt for California sprawl, believing it yields more balanced grapes.
“People want to get the grapes in the sun, get high phenolics, and make dark wine,” John Williams, the founder and winemaker of Frog’s Leap Winery, told Swinchatt and Howell. “They favor the huge differences that come from sun exposure, exotic yeasts, high maturation, oak perfume. Here, the fruit grows at a variety of levels in the plant, a variety of exposures, which gives a broad range of texture and flavor components.”
The following are the major wine grape trellis systems used in California.
Single curtain system: This is either a two-wire vertical trellis, known as simple curtain or California sprawl, common in hot, vigorous areas; or a vertical shoot positioning (VSP) trellis, more common in coastal areas. It is often used in high-production areas with moderate to high vigor, such as California’s Central Valley, with vine spacing between 6 and 8 feet and row spacing between 10 and 12 feet. It can be relatively inexpensive to install and maintain, with mechanization easy to implement for pruning, hedging, and harvesting. The biggest challenge with this system is controlling yields to ensure high-quality grapes.
Single curtain system with vertically divided foliage: Also called Smart-Dyson, this system is often used in new vineyards when vine vigor is too high for VSP but narrow row spacing is desired. It is widely used in coastal regions, especially where vine vigor is moderate to low. Vine spacing is six to eight feet and row spacing is seven to eight feet. The closer spacing affects competition among the plants and helps curtail the pressures of wind in coastal areas.
Vertically divided double curtain: Also known as Smart-Henry, this system is used in coastal regions when vine vigor is too high for VSP but narrow row spacing is desirable. Vines are cordon-trained at two heights to create upper and lower fruiting zones. The similar Scott-Henry allows for easier separation of the canopy through cane pruning. The separate fruiting zones allow winemakers to handpick grapes for different styles and bottlings.
Horizontally divided double curtain: The double curtain system is used to reduce canopy density under high-vigor conditions, whereas the lyre trellis is found in Cabernet Sauvignon and Merlot vineyards of moderate to high vigor in the North Coast of California. It is considered expensive to install and maintain.
The Future of California Vineyard Trellising
VSP has been one of the prevailing methodologies until recently, with growers questioning whether, considering climate change and consumer interest in fresher, more balanced wines, VSP is the best trellis system for the future.
In 2022, UC Davis published a Frontiers of Plant Science study that examined how to adapt wine grape production to climate change through trellising and irrigation, particularly in warmer climates. Recognizing that “trellis systems are utilized to optimize grapevine production, physiology and berry chemistry,” the study aimed to compare six trellis systems.
These included VSP, two modified VSPs, a single high wire (SH), a high quadrilateral (HQ), and a Guyot pruned VSP (GY).
According to the study, “An ideal trellis can promote grapevines’ photosynthetic capacity through optimizing light interception by the grapevine canopy. Most importantly, a suitable trellis can optimize canopy microclimate by providing sufficient solar penetration into canopies since solar radiation is necessary to enhance the berry composition . . . without excessive exposure to clusters to direct sunlight to avoid flavonoid degradation. There is evidence that grape clusters overexposed to solar radiation are prone to occur with some of the widely used trellis systems.”
VSP was singled out as a trellis system that can increase vulnerability of clusters to overexposure, and the study maintained that single high-wire trellis systems allow vine leaves to shade grapes better than VSP, where vine shoots are trained to grow up in vertical, narrow rows with fruit growing lower to the ground, allowing greater exposure to sunlight. How much sunlight depends on the site and the farmer.
Examining six different types of trellis systems and three different watering amounts, the study found that single high-wire trellis systems resulted in a more marketable yield for the amount of water used. It also found that single high-wire trellis systems acted as a good shade cloth, without negatively affecting grape color or quality.
FIGURE 1 Illustrations for the Trellis Systems Established at the Oakville Experimental Vineyard: (A) Traditional Vertical Shoot Position (VSP); (B) Vertical Shoot Position 60° (VSP60); (C) Vertical Shoot Position 80° (VSP80); (D) High-Quadrilateral (HQ); (E) Single High Wire (SH); (F) Guyot-pruned Vertical Shoot Position (GY). “h” stands for the cordon height from the vineyard ground.
“Cabernet sauvignon, Napa and Sonoma’s signature variety, needs sunlight, but excessive heat can dry out the fruit, costing growers thousands of pounds in weight per acre,” Caleb Hampton wrote in a November 2022 article for the California Farm Bureau Ag Alert. “It can also make the grapes too sugary. During fermentation, sugar turns into alcohol, and too much alcohol content masks the layered aromas that distinguish quality wines.”
Peter Nissen, the president of the Napa County Farm Bureau, noted in the article that the August and September heat waves that year resulted in wineries rejecting the fruit of some growers. “In all the years I’ve been farming, it was probably the worst heat event,” he said.
In anticipation of such an event, Napa Valley and Sonoma County growers had for years been experimenting with new trellis systems, such as moving from VSP to high-wire trellises, more common in typically hot areas, such as California’s Central Valley. The high-wire system is better at shading grape clusters with vine leaves and allows growers to reduce labor costs, as it’s more suited to machine pruning.
Adam Casto, the head winemaker at Ehlers Estate, in St. Helena, is moving to high-wire trellises as he replants part of the property’s 42-acre vineyard, planted predominantly to Cabernet Sauvignon, Merlot, Cabernet Franc, and Petit Verdot. “There’s been a pretty decisive move away from VSP over the last 10 years or so, but especially over the last five,” he says. “The vast majority [of growers] are either bringing up the fruiting wire or converting to cane pruning altogether. Climate change is increasingly the reason.”
He notes that moving the fruit zone up and planting vines farther apart help reduce intervine competition, especially because, as the fruit moves up, it requires more energy to transport nutrients from the trunk to the grapes.
But a single high-wire trellis also allows for more diversity in vasculature and sap flow, which also helps mitigate heat stress.
“It might be that homogenization in vines is unhelpful in increasing heat developments,” Casto says. “It’s such a deeply cultural expression, what it takes to make great wine. What is shifting is the idea that vines need humans to be great. [Trusting that] vines know what to do to be great, with some direction, is a sea change.”
Trellising isn’t being rethought only in Napa Valley.
“The VSP system is a dinosaur at this point,” Bryan Babcock, the winemaker at Babcock Winery & Vineyards, in the Sta. Rita Hills, said in an article for Wine-Searcher, “because it exposes the fruit to too much sun and maximizes labor and fuel consumption.”
Kathleen Willcox, who wrote the article, described Babcock’s experimental trellising system as entailing a raised platform that allows the vines to grow naturally, without wires, allowing the fruit and canes to float. He estimates that it saves him up to 30% in farming costs per acre annually and reduces bunch rot and heat damage.
Conclusion
California is in a golden era of vineyard development and management, where lessons from the past can be reconsidered to produce the best grapes in the future, while responding to the challenges of climate change and environmental and economic sustainability. Vineyard managers are also considering what trellising systems to use based on the challenges of finding labor to work in vineyards, and a growing consumer interest in wines of balance and freshness.
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Bibliography
Dokoozlian, Nick. “Trellis Selection and Canopy Management.” In Wine Grape Varieties in California, edited by Peter Christensen, Nick Dokoozlian, Andrew Walker, and James Wolpert, 16–21. Davis, California: University of California Agriculture and Natural Resources, 2003.
Geisseler, Daniel, and William R. Horwath. “Grapevine Production in California.” UC Davis, 2016. https://apps1.cdfa.ca.gov/FertilizerResearch/docs/grapevine_Production_CA.pdf.
Hampton, Caleb. “Winegrape Growers Turn to Higher Trellises to Beat Heat.” California Farm Bureau Ag Alert. November 2, 2022. https://www.agalert.com/california-ag-news/archives/november-2-2022/winegrape-growers-turn-to-higher-trellises-to-beat-heat/.
Long, Zelma R. “The Past Is the Beginning of the Future: Simi Winery in Its Second Century.” Interview by Carole Hicke. The Wine Spectator California Winemen Oral History Series, The Bancroft Library. Berkeley: University of California, Berkeley, 1991 and 1992. https://archive.org/details/pastbeginningfuture00longrich/page/n7/mode/2up?view=theater.
Swinchatt, Jonathan, and David G. Howell. The Winemaker’s Dance: Exploring Terroir in the Napa Valley. Berkeley: University of California Press, 2004.
Willcox, Kathleen. “Extreme Winemaking for Extreme Conditions.” Wine-Searcher. March 14, 2023. https://www.wine-searcher.com/m/2023/03/extreme-winemaking-for-extreme-conditions.
Yu, Runze, et al. “Adapting Wine Grape Production to Climate Change through Canopy Architecture Manipulation and Irrigation in Warm Climates.” Frontiers in Plant Science 13 (October 2, 2022). https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1015574/full.