The mycorrhizal network thrives underground, a vast fungal network that forms a symbiotic relationship with vine roots. It just might be the secret agent in the expression of soil terroir—if growers don’t till it away.
In 2005, when cousins Mimi and Ben Casteel were poised to take over their family winery in Oregon’s Eola–Amity Hills, they faced a problem: their oldest vines at Bethel Heights, planted in 1977, were battling phylloxera. On an east-facing parcel over the hill, they found a defunct Christmas tree farm which they could plant, to fill in for the suffering blocks. “It was a good site,” says Mimi, “but I had a bad attitude about it.” Commercial Christmas-tree farming is notoriously ruinous for the soil. “It’s chemically intense, heavily tilled; the ground is kept bare around the trees,” she explains. “It’s foundationally a disturbance regime.” It had rendered the soils inert.
Faced with a blank slate, Casteel took the first steps toward the rehabilitation of what would become Hope Well Vineyard, a project that has dominated her last decade; in that time, she has resurrected the property, above and below ground, with an eye to regenerating the microbial life of the soil, starting with the mycorrhizal fungi.
Mycorrhizae form a symbiosis with plant roots, an interdependent, mutually beneficial association, vastly extending the plant’s root system. (The word links two Greek word roots, myco-, meaning fungus, and rhizo-, meaning root.) Vignerons working with regenerative agricultural practices are taking active steps to cultivate healthy mycorrhizal populations in their soils; a number of those growers are based on the West Coast.
Photo by Paul Schreiner
Every spring, Ted Lemon takes a team of foragers into a forest adjacent to One Acre, his biodynamic property on the east ridge of Mendocino’s Anderson Valley. They collect leaf litter and fallen branches, most of it in some stage of decomposition and decay, and make a mulch, from which he makes a tea to spray onto his compost. When that compost is dispersed into his vine rows, he says, “it contributes to the mycorrhizal stream.”
At Hiyu Wine Farm in the Columbia Gorge, Nate Ready gathers forest detritus from the property’s adjacent wildlands and simply disperses it in his vine rows, providing fodder for the organisms that lie beneath the cover crop, contributing to the nutrient cycle.
Underground, plants and fungi exchange nutrients, fight off pathogens, assist each other through drought and manage other climatic extremes. Scientists are studying how this network might form other communication pathways. And growers are considering how a healthy mycorrhizal network may be fundamental to a wine expressing the character of the soil where it grows.
“It seems obvious to me,” says Eric Sussman of Radio-Coteau in the Sonoma Coast, who has farmed his vineyard biodynamically since 2012. “Healthy soil promotes subterranean activity we may not see. And when you farm a certain way, you preserve that.”
Photo by Aubrie LeGault
“What had grown here, the trees, the plants, all of this had been removed. I wanted to know what this place could actually taste like.”
—Mimi Casteel, Hope Well Farm
The bond between mycorrhizal fungi and plants is ancient; indeed, according to USDA plant physiologist Paul Schreiner, where terrestrial plant life is concerned, they are among the world’s first symbionts: “Mycorrhizae helped the earliest land plants get a foothold on primitive soils,” he says.
In healthy, well-structured soil you can see these networks with the naked eye, wending through the dirt in pale-veined pathways known as mycelia, composed of tiny filament segments known as hyphae. These penetrate root branches, forming a conduit for the fungi to convey minerals and nutrients to the plant—primarily phosphorus, but also potassium, copper and zinc. In exchange, the fungi receive carbohydrates and fatty acids, products of photosynthesis which the fungi cannot produce on their own.
Mycorrhizal networks exist in nearly every plant system on earth; they’re found in boreal and temperate forests, in Mediterranean woodland and chaparral; they’re abundant in grasslands, savannah, tropical forests, even tundra. According to Schreiner, some “80 percent of all plant species form this type of mycorrhizal association.”
In healthy systems, these networks crowd the soil with astonishing intricacy: Michael Phillips, an author and orchardist, notes in his book Mycorrhizal Planet that in one handful of forest dirt you can find 26 linear miles of mycelium threads. Not only do these lend structure to the soil, they broaden the roots’ surface area, help plants resist pathogens, contribute to drought tolerance and provide carbon sequestration.
Mycorrhizal networks have crept into the zeitgeist a great deal lately—impressive for an organism that rarely sees the light of day. They were explored in the 2016 bestseller The Hidden Life of Trees by the German forester Peter Wohlleben, a book which contained an afterword by plant physiologist Suzanne Simard, who’s received recognition in her own right for her studies of old-growth forests in British Columbia.
In the 1990s, Simard had set out to research why Douglas fir trees began to decline after birch trees, an unrelated species, were thinned from the same section of forest. In experiments tracking radioactive isotopes as they traveled through the root systems of the trees, she discovered that a mycorrhizal network linked the two species; they not only shared resources, but displayed previously unknown levels of mutualism, communication and cooperation, what she called a “collaborative wisdom.” “It was a social network for trees and plants,” she wrote. “They had forged their duality into a oneness, thereby making a forest.” And just like that, the “Wood Wide Web” was born.
Two years later, a character based on Simard drove the narrative of Richard Powers’ Pulitzer Prize-winning novel The Overstory, in which her field studies were sympathetically (and accurately) portrayed.
One year after that, the nature writer Robert MacFarlane’s Underland, about all manner of subterranean environments, from the Lascaux caves to nuclear waste graveyards and the catacombs of Paris, produced a vivid portrait of the Wood Wide Web through depictions of Simard and an English fungi researcher, Merlin Sheldrake. Both Simard and Sheldrake have recently authored books, their research centered on forests—complex, natural, often ancient biomes where mycorrhizal networks can flourish undisturbed for centuries.
Alongside this newfound attention is growing interest in the mycorrhizal networks that exist in agricultural settings, including vineyards. Those systems involve a different fungal group, called arbuscular mycorrhizal fungi (AMF) which are endomycorrhizae. Whereas ectomycorrhizae fungi, the forest variety, interact with root systems by essentially wrapping themselves around the finest roots and forming a sheath, endomycorrhizal fungi establish their connections inside the cells of the root, penetrating into some cells, forming an arbuscule (a branchlike tuft) inside the cell.
Much of what we know about AMF in U.S. vineyards comes from the work of two USDA researchers, Kendra Baumgartner, based in Davis, California, and Paul Schreiner, based in Corvallis, Oregon.
Both Schreiner and Baumgartner have published several studies examining AMF in vineyards. In fact, Schreiner calls grapevines “super-hosts,” as they are extremely amenable to robust mycorrhizal networks. “I’ve looked at a lot of root systems for a lot of plants,” he says, “and when grapevines are colonized, they’re just loaded. Even if the field is fallow, grapevines would get colonized better and more quickly than other plants.”
Both Baumgartner and Schreiner have designed several studies to determine how best to build up AMF in vineyards, to promote vine health and protect them from pathogens—all with an eye toward avoiding pesticides, fumigants, chemical fertilizers and other inputs that can destroy microbial populations and inhibit underground life. Their studies suggest encouraging AMF by crowding a property with plant species, providing abundant and diverse cover crops; Schreiner also sees benefits in planting a cover crop before the vineyard goes to ground, to boost existing AMF populations in the soil. He finds this is particularly important in the Willamette Valley, where the soils are especially poor in phosphorus.
Baumgartner’s and Schreiner’s research support conclusions similar to Simard’s: once the system is in place, it’s best for the vineyard and the microbiological life beneath the ground to be left alone. “When you till,” says Baumgartner, “you tear up any connection between the mycorrhizal filaments and the roots. The fungal connections are disrupted.”
“In the same way that we’re creating conditions where life forms will thrive, we’re creating conditions where unique wines can be made.”
—Nate Ready, Hiyu Wine Farm
Nearly two years before she put down vines, Mimi Casteel set about rehabilitating the property at Hope Well, starting with a systematic regeneration of the soils. “I felt it important to begin to replace what had been lost on this property through agriculture,” she says, listing “habitat, species diversity, stable soil carbon, organic matter.” Casteel spread tons of compost—initially, about sixty tons; all told, she estimates, she’s applied more than 250—turned organic matter into the soil and generally made the environment hospitable to mycorrhizal fungi. She planted 300 trees within the property’s wildlife corridors, planted shrubs for bird habitats, created woodpiles for other animals; she made the land attractive for bees and monitored their population. Casteel covered the ground with plants, aiming for no visible soil, anywhere; she planted 20 species of cover crop, and in the years since, has added hundreds more.
She designed her property so that her vines would occupy less than a third of the land, leaving the rest to wild areas, forested tracts, animal habitats and her family home. Casteel has an M.S. in Forest Biology from Oregon State, so she was familiar Simard’s work, as well as Schreiner’s, and knew of the importance of mycorrhizae—she believed those networks would ultimately play a role in her wines’ flavors. “So much of the life of this ground had been taken away,” she says. “What had grown here, the trees, the plants, all of this had been removed. I wanted to know what this place could actually taste like.”
One hundred miles away, in the Columbia Gorge, Nate Ready and China Tresemer purchased their property in 2010. An organic farm, it included orchards and a 14-acre vineyard. They renamed it Hiyu Wine Farm (Hiyu is a Chinook word meaning “big party”) and converted the property—some 30 acres—to permaculture, with the goal of creating a sustainable closed-loop in which the land provides what the farm needs.
They intended to graft over the vines—mostly planted to pinot noir and pinot gris—to some sort of field blend. But when Ready inquired about cuttings at Davis, he was surprised to learn how many were available to him; he went on to plant a huge varietal array. “How could I not?” he says. “It was crazy to me no one had tried this.” In all, they grafted 112 varieties on the property, mixed rows in mostly half-acre blocks, with varieties planted together based on whim, on curiosity, on regional or historic affinities or on hunches as to what would work well.
The Hypericum block, for example, is composed of a cross-section of Mediterranean varieties that Ready assumed were exchanged in ancient times between southern Italy and Greece—so assyrtiko and roditis are interplanted with fiano, greco di Tufo and verdicchio. They did the same with the orchard, regrafting over 50 different fruit and nut varieties onto pear and apple trees.
After Ready reseeded cover crops, built up an animal population, and inoculated with a mycorrhizal population (such preps are now available as commercial inputs), he finds the property is increasingly self-sufficient. All of his vineyards are no till; Ready tosses seeds in the spring, sometimes behind where his pigs are rooting, between rows; he prunes minimally, does no hedging or leaf-pulling and doesn’t drop fruit.
To look for signs of a healthy mycorrhizal network in a no-till vineyard is to rely on evidence of things not seen, starting with the soil, which, in a no-till block, is entirely out of sight. (Just to turn a spade would be a disruptive act.) But one reliable clue is that, comparatively, these vineyards are a mess.
Cover crops often stand two to five feet high, unmown and untended. Canopies are relatively unkempt, in part to contend with the cover crop as the vines seek out sunshine. Insects and birds abound, attracted by flowering plants. Animals roam freely—sheep, goats, llamas, chickens, ducks, guinea hens, geese, even cows, are common in the vine rows, their droppings, ubiquitous. They feed on grasses, on plant litter, on insects and on other animals (Ready thinks his pigs help with the mole and vole population in his vineyards). At Hiyu, cows have been known to poke their heads through open windows at the kitchen, greeting guests during meals and tastings.
In Hiyu’s early years, the vines seemed to operate on their own rhythms, ripening unevenly, often at different times, often very late, with a fruit quality that was, to Ready, similarly out of sync. But as the vines got older and the between-row plant population filled in and matured—and, presumably, as below ground populations did as well—Ready noticed that most blocks were reaching full maturity earlier, at lower sugars. And he noticed that co-planted varieties which had ripened at different times were now ripening at the same time. Even their flavors were beginning to coalesce.
“So, I started to wonder,” he says, “Are the vines adapting? Are they mutating? Or are they communicating?” And he assumed that mycorrhizal networks were, at least, part of the equation. “The fungal-bacterial networks have to be changing the plant’s access to nutrients and trace minerals,” he says, comparing what infiltrates into the underground environs to garrigue imprinting its scent on the plants above ground. “The way all those things are functioning together makes for this amazing entity,” he says, referencing the entire farm. And he describes wine as “a particularly wonderful access point” to that entity. “In the same way that we’re creating conditions where life forms will thrive; we’re creating conditions where unique wines can be made.”
Photo by Aubrie LeGault
No-till farming can be challenging: The delivery of nutrients isn’t as controlled as it might be with chemical fertilizers, and fewer passes through the vines can lead to some uneven nutrition. But both Ready and Casteel believe this results in a broader range of flavors in their wines. Replanting and reseeding is complicated, labor intensive, and often expensive. Properties tend to balance out over time but are vulnerable to disruption from outside threats: this past summer, Hope Well was inundated with voles, which had fled an adjoining property when that farmer, with his tractor and disc, destroyed the rodents’ habitat. They quickly took up residence at Hope Well, feasting on vine roots and threatening harvest. “We take it as far as we can,” says Casteel, “but we’re surrounded by conventional practices. We’re a refuge that is also trying to be a farm.”
But the vines survived. Indeed, says Casteel, the most salient difference afforded by a healthy mycorrhizal network is resilience. “Even in the places where we have weakness,” she says, “tissue samples from our vines show they are never low in phosphorus, which means the mycorrhizae are doing their job. And even the weakest looking plants are very resistant to pests. Finally, our vines don’t struggle to complete the season, they don’t give up the ghost when the season goes to shit.”
When asked about evidence of mycorrhizal communication, she often refers to the edge effect, an ecological phenomenon where transition is occurring. She points to Bethel Heights and the vines that were afflicted with phylloxera.
“With phylloxera, you have these lenses where there are sick and dying plants,” she says, “but around that lens you have some of your strongest, most resistant plants. Not only are those grapevines sharing information—‘I am in trouble, I am sick,’—they radiate a stress communication. And, of course, the ones at the edge of that communication pathway receive it first; you often see super healthy vines at the edge of affected blocks.”
Casteel often observes weaker vines at the forest’s edge, where the vineyard ends. “But,” she says, “those vines that appear weak are in dynamic communication with a diverse and powerful habitat. They have to be scrappy, they have to negotiate and share in order to get what they need.” She believes that helps intensify the resulting wine’s unique expression. It’s why she keeps blocks small and breaks them up with other systems. “I like to amplify what’s there,” she says, “put in more habitat and watch what happens.”
Further Reading
As this story suggests, mycorrhizal fungi are the subject of an ever-increasing number of books, papers and articles in recent years. Here is a roundup of books mentioned in or consulted for the story.
The Overstory, by Richard Powers. This Pulitzer Prize-winning novel from 2016 examines the interconnected life of humans, plants and trees from a number of perspectives, including that of forest researcher Patricia Westerford, whose discoveries in Canadian forests are loosely based on those of Suzanne Simard.
Underland, by Robert McFarlane. MacFarlane is a nature writer who, in this book, explores life as humans experience it underground. This takes him to some unusual places, sinkholes, caves, catacombs, underground rivers and tunnels. Along the way he profiles Suzanne Simard and a young contemporary of hers, Merlin Sheldrake, both researchers of the Wood Wide Web.
Last year, Sheldrake published Entangled Life, focused on all aspects of the fungal universe. Simard’s book, based on her years of research, Finding the Mother Tree, has a publication date of May 4, 2021.
For practical guides to the mysteries and the uses of mycorrhizal fungi, several winegrowers recommend Mycorrhizal Planet by Michael Phillips. Phillips is an apple farmer and orchardist who has put together an introduction to the biology of fungi and their essential role in agriculture. Others recommend Mycelium Running by Paul Stamets.
Nearly every grower I spoke to, especially those practicing no-till farming, took inspiration from the work and life of Masanobu Fukuoka, a Japanese rice farmer and agricultural theorist. Along with Rudolf Steiner, Fukuoka is considered one of the most influential proponents of natural farming in the last century. His essential book on the practice, The One-Straw Revolution, first published in 1975, is a thoughtful practicum on managing chemical-free, no-till, laissez faire practices—what he refers to as “do-nothing” agriculture.
To taste the wines of Ted Lemon, Eric Sussman, Nate Ready and Mimi Casteel, you might find they have an extra gear. For one thing, they’re not oriented to fruit expression; they exist in a savory realm that’s wholly their own. The pinot noirs of Littorai and Radio-Coteau are thoroughly Californian on one level, but there is always a savor that takes you out of the sunshine, down into the earth. Nate Ready’s patchwork field blends are designed to be unorthodox, and he further courts outré flavors and textures by leaving his fruit unsorted; by and large, that fruit goes into the fermenter as an unretouched snapshot of where it was grown.
When I taste the wines of Hope Well and Hiyu, inevitably a single word comes to the forefront of my mind: more. There are recognizable flavors, aromas and textures, but there are more of them than I can comfortably direct my attention to. It is complexity, yes, but it’s also a kind of crowded life in the glass, an analogue, perhaps, for the crowded, abundant, microbial commotion of the soil beneath the vines.
Mimi Casteel’s goal is simple, to have her wines be a megaphone for place. She worries sometimes that the voices aren’t modulated, that the soil isn’t given every opportunity to be heard in the face of so many other intrusions of expression.
“The tragedy of post-modern winemaking is that we don’t ask ourselves what we mean by terroir,” she says. “We don’t poke at it. So often we’re just tasting the abiotic factors of a site. You can taste climate; you can occasionally taste the relative elevation. You can certainly taste winemaking. Is that interesting? Sure. But the fact is we’re looking at terroir in the context of a very, very loud climate.”
Without a healthy mycorrhizal network, the soil doesn’t have a chance—but in a healthy network, its voice is amplified. “When it comes to the soil, it isn’t possible to have too much life in one place,” says Casteel. “Life begets life; biology works exponentially. The more you have, the more you can have. That’s what I want to communicate. It’s the only hope we have of retaining any sense of what it means to say, ‘I can only do this here.’”
Patrick J. Comiskey covers US wines for Wine & Spirits magazine, focusing on the Pacific Northwest, California’s Central Coast and New York’s Finger Lakes.
This story appears in the print issue of April 2021.
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