In vineyards, grapevines are the only plant used for actual production. But there is often a considerable amount of other vegetal growth—whether wild plants or selected crops of legumes, cereals, or grasses—that can help facilitate viticulture and support the long-term health of the vineyards.
Set between the rows or under the vines, this vegetal cover serves a variety of functions. “Cover crops are useful in the vineyard to avoid erosion and aerate the soils,” says Jean Hoefliger, a consulting winemaker at Alpha Omega Winery in Napa Valley who also works with vineyards in Spain and Italy, among other wine regions. “They also supply nitrogen, which is needed with the increased microbiological activity that comes with better soil aeration.” In places like Napa, Hoefliger says, cover crops can also moderate excessive vine growth early in the season by creating competition for water and nutrients.
By understanding the various functions of cover crops and adapting their use to local growing conditions, winegrowers can reap a number of benefits—and even cut costs, notably by reducing or eliminating the need for herbicide applications.
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Steve Roche, a South African viticulturist who is currently the vineyard manager at Clos du Soleil winery in British Columbia, Canada, points out that cover crops and vegetation can be crucial in keeping the soil in place. “In South Africa, 80 percent of the rain comes in the winter,” he says, “and it can rain several days in a row, so there can be lots of runoff. Cover crops … prevent erosion. And when the dry weather comes, you can flatten them to preserve moisture in the soil or mow them down or mulch them to help improve the soil.”
Maintaining a vegetal cover is a lot more effective in supporting and preserving soil than cultivating it or keeping it bare by means of herbicides, according to Justine Vanden Heuvel, an associate professor at Cornell University’s School of Integrative Plant Science. In 2017 she concluded a multiyear research project on under-vine cover crops that demonstrated positive results in avoiding erosion and runoff, and nutrient or pesticide leaching. “I think the industry needs to think more about soil preservation,” Vanden Heuvel says. “This idea that we can grow vines with open, bare soil, is not a good one.” Her research also showed that soil quality is improved by the presence of vegetal cover—the soil becomes more porous and offers greater water availability.
Nutrients and Vigor
Cover crops can be used in a variety of ways to manage vineyard growth, whether invigorating or moderating it. They can even be used to increase yields and productivity in exhausted blocks. A famous example of this is winemaker Cathy Corison’s Kronos Vineyard, an old-vines parcel in Napa Valley that was significantly depleted and low-yielding when she took it over in 1995. Winter cover crops like peas, clover, and mustard have significantly helped increase nitrogen content in the soil at Kronos—and helped restore vineyard health and yields.
Vanden Heuvel’s work also shows that cover crop selection can have important effects on vineyard balance and vine vigor. Her study focused on vineyards in New York State’s Finger Lakes region, where the effects of such cover crops as white clover, turnips, radishes, and alfalfa were compared with those of the natural vegetal cover. While some crops competed significantly with the vines and limited growth, others did not. “Some cover crops have very little effect on vine vigor, like buckwheat, says Vanden Heuvel. “But this can be good, right? If you have lower-vigor vines, growing buckwheat would still reduce erosion risks by limiting the amount of open soil, without affecting [the vine’s] growth. We also found that other cover crops, like chicory, will significantly reduce vine size, but without reducing yields.”
One of the Cornell study’s goals was to compare the results of using cover crops with the still common practice of using herbicides like glyphosate to kill off plants under the rows. Vanden Heuvel found that the judicious use of cover crops is much more advantageous than using herbicides. “Here in the Finger Lakes, we have vines that we have to hedge four or five times in the growing season [because of vigorous growth],” she says, “but then you apply herbicide to make sure [the vines] don’t have competition. Doesn’t make much sense, right?” Her study also found that maintaining cover crops instead of using herbicides reduces viticulture costs.
Another advantage of cover crops is that they provide vineyard operators a lot of options. For example, if growers plant chicory—which competes for water and nutrients with the vines, reducing their vigor—they can switch to a different plant, like buckwheat, says Vanden Heuvel. “You’re definitely not wedded to a single plant.” In dry years—or in drier, hotter climates—when the vines struggle more, growers can choose to mow or cultivate the under-vine crops to reduce competition.
Sometimes, the best cover crop is not a cover crop at all but native plants that are allowed to grow naturally in the vineyard. For instance, Jason Lett, the owner and winemaker of Eyrie Vineyards in Oregon’s Dundee Hills, has found success using a permaculture approach—essentially never plowing but letting vegetation naturally establish itself between and under the rows. The approach encourages biodiversity, lets the vineyard find balance in its ecosystem, and protects the soil structure so that it can build itself over time.
Clos du Soleil’s Roche takes a similar approach in the winery’s organic vineyards, allowing plants adapted to the local conditions—in particular, the dry summers—to establish themselves. This benefits soil structure and biodiversity, he says—“The naturally occurring flora is especially helpful in organic viticulture because it helps [attract] beneficial insects.” Alternatively, leafy plants under the rows can help keep pests like leafhoppers away from the vines by providing a preferred food source.
For Roche, who has also worked at Hidden Bench, an organic producer in Ontario’s Niagara Peninsula in eastern Canada, the general idea is to allow vineyards and cover crops to adapt to specific conditions. Sandy soils, he says, can benefit from having more organic material added to them, for example, while loamier, heavier soils might not. And heavy clay soils can benefit from dandelions and other plants with deep roots, which break up the soil and allow it to breathe and manage water better. “You shouldn’t fight with nature,” says Roche, adding, “I certainly prefer to work with it.”
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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.