Flexible grapes like Chardonnay and Syrah can thrive in both cool and warm climates, but most grapes have to be grown within a narrow range of temperatures to develop, taste and smell their best. Pinot Noir’s range, for example, is between 57 degrees Fahrenheit and 61 degrees Fahrenheit.
Cover crops, flora grown to enrich and enhance soil, used to be part of the terroir-driven approach to farm and grow grapes. However, for many years, they were either not used or treated as a one-size-fits-all way to boost soil health, limit erosion and boost biodiversity.
This was the result of a more industrial style of farming embraced during the mid-20th century. Wild grass and wildflowers suddenly seemed untidy and a sign of undisciplined growers. “Weeds” were out, replaced by chemically manicured strips of short, naked grass.
How times have changed.
These growers are refining their approaches and identifying cover crops that work for their particular climate, soils and winemaking goals.
Bordeaux, France: Planting Trees in the Vineyard to Amplify Cooling Effect
Bordeaux is France’s largest AOC (Appellation d’Origine Contrôlée) with 274,000 acres of grapes under vine. Merlot, considered the world’s most vulnerable grape to climate change, accounts for more than 66% of red grape acreage.
In recent years, sudden frosts, hailstorms, droughts and extreme heat have devastated harvests. In 2021, spring frosts cost the French wine industry an estimated $2.1 billion.
Bordeaux’s winemakers are responding. More than 75% of growers are now certified sustainable, up from 65% in 2019, according to the Bordeaux Wine Council. Many growers combat the effects of extreme weather with innovative approaches to cover crops.
At Château La Clotte-Cazalis, Marie-Pierre Lacoste knew she had to take extreme measures.
“We produce mostly Sauternes here, which is a sweet wine, but it still needs balance,” she says. “The warming climate was making the grapes lose some of their aromatic freshness, and we were having trouble balancing the good mold of botrytis with the bad mold.”
In 2015, she began to plant cover crops dominated by legumes and cereals. She also allowed the grass and native plants to grow wild. Almond, apple, cherry, peach and pear trees were also cultivated in the vineyard.
“We planted trees every 12 rows,” says Lacoste. “We farm organically without chemicals, and all of the trees and cover crops that we bring in are native to the region. The cover crops keep the soil cool, increase fertility and health of the soil and the vines. [They also] boost aromas, freshness and acidity in the grapes, while also reducing humidity, which helps take care of the bad molds.”
By using cover crops in tandem with the vineyard trees, Lacoste says the effects are amplified, and her grapes “balance and fresh aromas have returned.”
Champlain Valley, Vermont: Using Cover Crops to Highlight Terroir
La Garagista’s Deirdre Heekin has 11 acres of hybrid grapes like Frontenac Gris and Marquette under vine in the Champlain Valley and at her Barnard estate. She began to use cover crops in 2008 as she prepared new vineyards and began to convert others from synthetic to regenerative farming.
“I have planted covers of clover, buckwheat, sweet pea, vetch, daikon and winter rye,” she says. “Winter rye was used as a cover crop seeded in the fall for early-spring sprouting. The other covers I used were seeded together or individually, depending on what was needed.”
Daikon radish helps naturally till her clay-heavy soil and boosts soil health. In the past decade, she’s discovered how each plant targets problems in the field.
“The cover crops keep the soil cool, increase fertility and health of the soil and the vines.”— Marie-Pierre Lacoste, winemaker, Château La Clotte-Cazalis
“Dandelion works like daikon,” says Heekin. “I love working with buckwheat because it’s a quick cover in our short growing season, and it breaks down quickly [to feed] the soil readily. Its blossoms attract pollinators and other beneficial insects. Clover works well here because it is an easy nitrogen fixer and it is lower-growing, which can be a benefit for under-vine flora, as we don’t do any cultivation under vine. Vetch can work in the same way.”
The cover crops have had some unexpected benefits.
“We find that working with the native plants imprints something very specific on the wines, like a garrigue,” says Heekin. “In one of our vineyards, the plants grow up into the canopy, things like purple aster, daisy fleabane and goldenrod, which are full of essential oils that are antifungal and antimicrobial. In tandem with our spray program, which utilizes plant teas made from plants in the vineyard and homeopathic doses of minerals, these native plants help keep the vines healthy from diseases like mildews and anthracnose, black rot. And those essential oils seem to also infuse the fruit with a character and sense of place.”
Alentejo, Portugal: Curating Native Crops for Soil Fertility, Erosion Control
Portugal’s Alentejo region has faced crippling heat waves and droughts that have reduced harvest by 50% in some places. Alentejo has 56,500 acres of grapes under vine and a regional eco-certification known as Wines of Alentejo Sustainability Program.
Launched in 2015, the program has 483 members that represent about 50% of the acreage.
The group seeks to tackle environmental challenges, reduce reliance on chemicals and institute greener farming with biodiversity initiatives that include cover crops.
Producers like Herdade do Esporão, which has about 1,600 acres under vine, experiments with 180 or so grape varieties across an experimental plot to find which withstand heat and drought best. It also employs organic growing methods and cover crops.
“About 15 years ago, we began using cover crops to avoid the need to till,” says winemaker Sandra Alves. “We were becoming increasingly concerned about the environment, and we found that the cover crops improve soil fertility and also control erosion and boost biodiversity.”
The team has experimented with both permanent and temporary cover crops, sown with a single or several plant species.
“We’ve adapted our strategy after finding that planting commercial seed mixtures sometimes contained invasive species,” says Alves. They began to seek out promising, native cover crops on the estate. They now focus on native crops like subterranean clover, barrel light, snail medick and tall fescue, chosen with production goals and the many soil types on the estate.
Trentino, Alto Adige: A Diverse Mix for Optimal Vine Health
Italy’s Alto Adige region has around 5,000 winegrowers that grow grapes across 13,700 acres. Currently, only about 7% of its plantings are certified organic, but Alto Adige Wines hopes to change that. Its set a 2030 Alto Adige Wine Agenda that includes a ban on synthetic herbicides, optimizing water management and improving soil health.
Certified organic Thomas Niedermayr’s Hof Gandburg has 12.4 acres of vines across seven sites. In each place, cover crops are utilized for a specific purpose, says Thomas Niedermayr, a winemaker and grower.
“We use leguminous crops like field beans and sweet peas [that] draw in nitrogen from the air and enrich the soil,” he says. “We use leguminous grasses like alfalfa and melilot to fix nitrogen and improve drainage, which helps bring oxygen and water deep down into the roots.
“They also attract beneficial insects and provide nectar and forage, especially for bees,” he says. “While they grow up to five meters high and can compete with the vine, they also absorb minerals, which are then available for the vines.”
Cruciferous plants like canola and mustard provide ground cover and shade, feed insects and leave biomass that nourishes the soil. Herbs like caraway, wild carrot and phacelia attract beneficial insects and break down phosphorus in the soil. Niedermayr also plants sunflowers, buckwheat and grains to absorb minerals like copper and help improve drainage.
“The great diversity of roots influences nutrient availability and supports the overall vitality of the vine,” says Niedermayr.
Burgenland, Austria: Combatting Heat Spikes, Drought with Careful Cover
In Austria, the rapidly warming climate is threatening its trademark grape, Grüner Veltliner. On average, temperatures have risen more than than 3.6 degrees Fahrenheit in Austria since 1880, outpacing the global average of 1.9 degrees. The Austrian Winegrowers Association unveiled a certification in 2015 that rates producers on their use of chemicals, biodiversity, soil fertility and more.
For Franz Weninger, who farms Weingut Weninger biodynamically, terroir-driven cover crop choices are a foundational aspect of his plan to withstand higher temperatures and lower rainfalls. Weninger uses a range of native herbs, legumes and grasses.
He’s become so invested in the project that he has created a cover crop seed bank suitable for a variety of growing regions and soil types. He hopes to make the seeds commercially available soon.
“With cover crops, I copy what a cow eats,” says Weninger. “We have a blend of 60% grass, 30% legumes and 10% herbs. And because I want my wine to taste of my place, I use native plants.
“Terroir, in many ways, comes down to the microbes and yeast found in a particular place. A diverse cover crop will create more complexity in the glass.”
It took time for him to get the right balance.
“[With] too many herbs and too much grass…my wine gets thinner and with more structure,” he says. “That is nice for ageable wines. But for drinkable wines, you want less of that.”
There might be too much of a good thing with cover crops. In the spring, he often removes or reduces the height of his cover crops so the vines don’t have to compete with water or energy.
Napa, California: Every Vintage Requires a New Blend
Napa is contending with warmer temperatures and devastating wild fires, not to mention long-term drought (on average, the California growing season has warmed 2.3 degrees Fahrenheit between 1895 and 2018, according to the Napa Vintage Report).
Kirk Grace, director of vineyard operations at Stag’s Leap Wine Cellars, tries to mimic nature as best he can.
“I use vines as our overstory, and a grassland cover crop as the understory,” he says. “We have found that short-statured annual grasses are often best for us. They help enrich the soil, giving the microbes something to feed on. That community of healthy organisms populate the soil and attract other healthy forms of life.”
Without the cover crop, he says that the soil becomes “sterile, especially when chemical use gets out of hand. Excessive tilling can worsen the health of the soil, but because nature abhors a vacuum, tougher weeds and microorganisms move in. It becomes a vicious cycle, with soil that becomes increasingly degraded.”
Grace says that cover crops reduce erosion, aerate soil, aid with water penetration and keep the community of microbes healthy, but each type offers something slightly different.
“A diverse cover crop will create more complexity in the glass.“— Franz Weininger, winemaker, Weininger Weingut
“We customize our strategy every year, depending on what’s happening,” says Grace. “Biomass-producing crops, like peas and beans, will fix nitrogen and invigorate the soil. Maintenance cover crops, like annual grasses and clovers, are intended to maintain vineyards in their current state. Devigorating cover crops like perennial grasses are intended to throttle back over-vigorous vines.”
Cover crops won’t make or break a vineyard. But in a more extreme environment, they can provide a foundation for health and help create more precise, terroir-driven wines. They also make growers see the vines in a completely new way.
“If a new plant arrives on the scene, it can forecast things we may need to be aware of to provide the best care in the vineyard that we can,” says Heekin. “Certain plants thriving in certain soils might tell us we need to do something like apply compost. These native covers always offer the solutions we need. We just need to be attentive enough and do our homework on what these plants mean in the vineyard landscape.”