Wine

Examining the Effects of Vine Vigor on Grapes

Winegrowers and researchers weigh in on site selection, canopy management, and other strategies to manage growth and ripeness

Vines at Eyrie Vineyards
Vines at Eyrie Vineyards. Photo courtesy of Rémy Charest.

Winegrowing is very much about balance. A vine needs enough canopy and growth to ripen the grapes, but if it has too much, problems can arise—including ripening issues, ironically. In order to find that balance, understanding and managing vine vigor is essential.

On a very basic level, vigor refers to the amount of growth—shoots, leaves, and grapes—produced by a grapevine over the course of a season. If a vine has many long shoots as well as larger leaves and yields a large crop, it has a lot of vigor. If the vine has trouble growing shoots up to the trellis wires and bears a very limited crop, it’s low on vigor.

Alan N. Lakso, a professor emeritus at Cornell University’s School of Integrative Plant Sciences in New York’s Finger Lakes region, explains that interpreting vigor can be complicated. “If you think of vine shoots, and one is very long and the other one is short, the long one has more vigor, and everyone is on the same page about that,” he says. “However, for the vine as a whole, it’s more complicated. With pruning, if you leave only a few shoots, they’ll grow long and be more vigorous. But the total growth of the plant would be greater on a vine where you left a lot of shoots.” A plant might have more energy than another but show less overall vigor because it’s been pruned back more heavily.

Patricia Skinkis, a viticulture extension specialist and an associate professor at Oregon State University’s College of Agricultural Sciences in Corvallis, also notes that vine vigor can be measured in a number of different ways, such as by the vine’s rate of growth or by winter pruning weight, which is the amount of material removed after the growing season. “The term vigor,” she says, “becomes a matter of debate when it comes to researchers.”

Too Much of a Good Thing

The term vine vigor can also have a different meaning for growers than it does for researchers. “In winegrowing, vigor tends to be interpreted on the high side,” says Skinkis, who notes that most often, the concept becomes a preoccupation when there is excess vigor. “For growers and vineyard managers, it’s about shoot growth, lateral growth, things that need to be managed.

”Although it might seem as though this growth would be beneficial, a vine that has too much vegetal growth—big canes, big leaves, lots of lateral shoots (also known as suckers)—will have a crowded canopy, which creates excessive shade, slows ripening, and hinders airflow, which in turn encourages the growth of fungal diseases. Jason Lett, the owner and winemaker of Eyrie Vineyards in Oregon’s Dundee Hills, once faced such issues in vineyard sections that were closely planted on rich soils. He changed the trellising system to channel the excessive vigor into a more open and widely spread canopy, restoring airflow and reducing disease in the process—and, consequently, improving grape quality. “We used to cut bunches because they were stuck in foliage and had powdery mildew,” he says. “Now, we only cut them when there is uneven ripening.”

Vines at Eyrie Vineyards
Vines at Eyrie Vineyards. Photo courtesy of Rémy Charest.

If energy goes to shoots and leaves, grape maturity can be affected. Lakso explains that in studies done on Cabernet Franc in the Finger Lakes, ripening problems appeared when there was too much vigor. “Lots of variations were used in the number of shoots and growth levels,” he says, “and what we saw is that when there is more vigor, the grapes retain more methoxypyrazines. White [grapes] tend to be more tolerant of these situations, but in red grapes, the skin-to-volume ratio goes down when there is lots of vigor, meaning [there’s] less concentration—and green character remains.”

However, research conducted by Skinkis in Oregon has shown that crop thinning—dropping grape bunches in order to reduce the crop load and foster better ripening—has limited effects on a plant’s overall vigor. This has led to questions about the usefulness of the practice in achieving the desired results. “It’s likely,” she says, “[that] the plants can hold all that fruit.”

External Factors

The vigor of a plant also depends on other factors, such as water availability, soil fertility, and rootstocks. “If you go to a vineyard and you see vines that are on shallow soil,” says Lakso, “and others are in deep soil, the ones with more water and more soil will grow more, and the vine as a whole will have more vigor.” Looking at vigor becomes a very different exercise in Virginia, for example, where summer precipitation is plentiful, than in California or Washington, where summers are dry and many growers use deficit irrigation to keep the vines alive and productive.

Nutrients are significant as well. If a vineyard is planted on rich soil, especially agricultural soil that was heavily fertilized, vigor can increase considerably. “Vines really want to grow,” says Lakso. “I once saw a single shoot that measured 62 feet long [growing] around a pergola at a private home. If you give them water and nutrients, they’ll grow like crazy.” In drier climates where resources are less readily available, using cover crops between rows, under vines, or both can create competition for nitrogen, other nutrients, and water, making the technique an effective tool for moderating vine growth where necessary. When water and nutrients are more plentiful, cover crops are less effective at limiting vigor because there’s plenty of resources to go around and all the plants can grow without being in any significant competition.

Jean Hoefliger, a winemaker at Alpha Omega Winery in the Napa Valley and a consulting winemaker for other estates in Priorat and Tuscany, among others, points out that seasonal variations in the availability of water and nutrients can have powerful effects on the vines’ behavior. “This year, in Napa,” he says, “we’ve had lots of rain, especially in May, and that has created a push for very strong vegetative growth in the vines. The water gives the vines a signal that resources are abundant and the plants react accordingly.” But Hoefliger adds that when the vines are set up for abundance, “once the weather becomes hot and dry, the plants have a greater tendency to shut down, which can affect the fruit’s development. The fruit set is also negatively affected because the energy is all going to leaves and shoots.” There are, however, means to manage such reactions to weather changes, like leaving extra shoots on the vines early in the season to capture rising sap and vigor, and then cutting them later on so the plant can shift its focus back to ripening grapes.

Conversely, Hoefliger adds, very dry and hot years like 2003 in Bordeaux or 2015 and 2016 in California can negatively affect the vines’ growth so much that the effect extends into the following vintages. When a plant is insufficiently vigorous, grape quality can also be impacted. “If the vine isn’t strong enough,” he says, “acid drops out very quickly and berries tend to get dehydrated.”

To Kalon Vineyard
Bush vine from the 1940s located at To Kalon Vineyard in Napa Valley. Photo courtesy of Rémy Charest.

Well-grounded Vines

Rootstocks can also exert an influence, and many are cited as either increasing or restricting vigor. It’s hard to draw general conclusions, though. Results of their use vary, especially between wetter and drier climates. Rootstocks that restrict growth in many California vineyards can be fairly generous once planted in the water-retaining Jory soils of the Willamette Valley, or in wetter northeastern U.S. regions. Also, as Lakso points out, the effects of rootstocks on vines are relatively moderate compared with their effects on other plants. “In fruit trees, there are rootstocks that will turn very tall varieties into dwarf trees that stop growing at two or three meters high,” he says. “In grapevines, the effects are nowhere near that.”

At Eyrie Vineyards, Lett has been researching new options for rootstocks in his vineyards, as sections of older, own-rooted vines are succumbing to phylloxera. The search has been proving difficult. “It’s a bit of a tall order to find rootstocks that give you moderate vigor, drought tolerance, and good acid retention,” he says. “Also, when you read descriptions from nurseries, one will tell you that such and such rootstock is drought resistant, and the other one tells you the opposite, and the same thing for moderating vigor.” This has led Lett to try to find his own, distinctive rootstocks—while trying to envision the effects that climate change, causing drier, hotter summers, might have for dry-farmed vines in Oregon.

From site selection to canopy management and the use of cover crops, there are many ways in which winegrowers and vineyard managers can work to achieve the desired vigor—or put another way, the desired balance—of their vines. Though Skinkis cautions that the concept of balance irks some researchers because it’s hard to quantify, she still thinks it’s useful. “It’s a true concept,” she notes. “The vines need to reach a certain balance to ripen fruit and be productive, whether it’s natural balance or something we need to do to help them reach it. We have a lot of control: We can use shoot thinning, leaf removal, hedging, crop thinning, and other means to moderate vigor.” Solutions, however, are far from uniform; approaches used to manage vigor and establish balance need to be specifically tailored. “It’s really based on what you find on your site and in your region,” Skinkis says. “There is a site effect.”

Rémy Charest is a journalist, writer, and translator based in Quebec City, Canada. He has been writing about wine and food since 1997 for various Canadian and American print and online publications, including Chacun son vin/WineAlign, Wine Enthusiast, Le Devoir, Le Soleil,  EnRoute, Palate Press, Punch Drink, and Châtelaine, and has been a regular radio columnist for CBC/Radio-Canada. He has also judged national and international wine competitions, notably the WineAlign National Wine Awards of Canada, the TEXSOM International Wine Awards, and the International Rosé Championships.

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