In this latest interview article, I asked a handful of growers about their thoughts and practices as pertains to soil health. As you will see, the questions elicited a lot of passion! Many answers are lengthy, but are well worth reading through, as they contain a great deal of insight and information.
When talking about wine, we in the trade often namedrop soils as if their effects on the resulting wines are understood and obvious. Such mentions are not only often intellectually tenuous, but, according to these vineyard managers, shallow as well. As Martin Di Stefano from Zuccardi in the Uco Valley points out, soil is not just a “physical substratum,” it is a living thing, subject to its own phases and cycles independent of vintage characteristics. Because of this, its effects on wine are more complex than is typically discussed.
For example, low nitrogen sites can sometimes lead to stuck fermentations, which can impact wine depending on how this is managed. Cover crops can be used to create resource competition, which can limit vine growth in vigorous sites, a healthy microbiome converts inert soil compounds into nutrients that can be taken up by plants, and the presence of rodents can reduce soil compaction and increase aeration. These examples link back directly, if subtly, to wine quality.
I also enjoyed the discussion surrounding some of the more practical considerations. Pete Richmond tends vineyards for a range of clients and must take their budgets and philosophies into account when creating a farming plan. He contemplates the benefits of organic cultivation versus the extra fuel burned to apply the many treatments. And more than one grower mentioned that purchasing seeds for cover crops is actually quite expensive, and that budgetary limitations are often a factor in the final selection.
In short, soil type is only one aspect of a vineyard’s identity. Soil health, its microbial ecosystem, and the farming methods applied are also of considerable import.
Contributors to this article are Pete Richmond from the Silverado Farming Company in Napa, Martin Di Stefano from Familia Zuccardi in the Uco Valley, Mimi Casteel from Hope Well Wine in the Willamette Valley, Roberto Santana from Envínate, which works with a handful of sites across Spain, and Vanya Cullen from Cullen Wines in Margaret River.
Clockwise from top left: Pete Richmond, Martin Di Stefano, Mimi Casteel, Vanya Cullen, and Roberto Santana.
Kelli White: Tell me about the vineyards you farm. How many are there? How big are they? What are they like in terms of soil, climate, and varietal composition?
Pete Richmond: We farm both Napa and Sonoma—about 50 acres in Sonoma and 600 in Napa. Sonoma is all Pinot and Chardonnay, from Sebastopol to Bodega Bay. Napa is Cabernet Sauvignon, Sauvignon Blanc, and a little Zinfandel. Our Napa vineyards range from south to north and into the hills on both sides, nothing into the outer valleys of Napa.
Martin Di Stefano: We are farming five different vineyards for the Zuccardi range, with a total surface of 160 hectares, and two vineyards for the Santa Julia range, with 150 hectares. All of them are in the Uco Valley, which is the coolest winegrowing region in Mendoza. The altitudes run from 1,000 to 1,400 meters above sea level, so we have many different microclimates. In terms of soil, all of them are alluvial, created with sediments carried down by two rivers, Tunuyán and Las Tunas, from their source in the high Andes. We normally have subsoils with round-edged stones, and topsoil of sand or sandy loam. In some areas (Paraje Altamira, Gualtallary, San Pablo), the stones are covered with a large crust of calcium carbonate, which makes the soils really calcareous. In terms of varietal composition, our main variety is, of course, Malbec, but we also farm Cabernet Franc, Cabernet Sauvignon, Bonarda, and some Tempranillo, and in whites, Chardonnay, Verdejo, and we are starting to play around with Sémillon and Riesling.
Mimi Casteel: I farm Hope Well, my farm and vineyard, and my wines are exclusively from this site. Hope Well is 80 acres, with 25 under vine. We have a small, one-acre orchard and a vegetable garden, but most of our land is in habitat. We are located on the east side of the Eola-Amity Hills. The property has volcanic, marine sediments and some alluvial sediments as well—in other words, we have all the soil types. The vineyard is roughly 65% Pinot Noir, 20% Chardonnay, and 15% Riesling. The east side of the Eola-Amity Hills faces the Cascades and the Great Basin beyond, so it does tend to be slightly warmer than the west side from a meso-climatic perspective. I have a highly wind-affected site, like much of Eola. However, the Willamette Valley has a very warm growing season, and in the summer, it is quite xeric, so we have powerfully hot days during our protracted growing season offset by nights that get quite cool thanks to our position with respect to the Van Duzer Corridor. I also work with Larry [Stone] at Lingua Franca, which includes the Larry Stone Vineyard, which is 66 acres, only Pinot Noir and Chardonnay, also on the east side of the Eola-Amity Hills, and their leased Chardonnay site, Bunker Hill, in the hills south of Salem. Larry’s vineyard also has several soil types, much like mine, with volcanic soils at the top and sedimentary soils on the bench and lower areas. The Bunker Hill site is just five acres of Chardonnay. It is volcanic as well and somewhat cooler and quite protected in a unique hill chain that has very close proximity to a bend in the Willamette River, which I believe also contributes some thermal protection.
Roberto Santana: We work mainly in three different areas of Spain: Ribeira Sacra (6 hectares) in Galicia where the fruit goes to our Lousas wines, Almansa and Manchuela (8 hectares) for our Albahra wines, and three different areas in Tenerife (16 hectares) for our Táganan, Benje, Migan, and Palo Blanco [wines].
Most of our vineyards are small (between 0.2 and 1 hectares) so vary in terms of soil and climate, but to speak generally the soils are mainly, in Ribeira Sacra, broken slate, gneiss, and schist; in Almansa and Manchuela, chalky and sandy; and in Tenerife, mostly basalt, but depending on the area, we have different kinds of volcanic soils. Some vineyards are located close to a volcano, so the soils are covered with a layer of ash.
The climates also range but are mainly, [in] Ribeira Sacra, Atlantic weather, rainy and high humidity, [and in] Almansa and Manchuela, continental weather and dry. Tenerife is in a subtropical area, but the north is influenced by the alisios [“trade”] winds, which make the weather fresher and more Atlantic. The temperature stays constant throughout the year.
We work with the traditional varieties in each place. [In] Ribeira Sacra, mostly Mencía, with Merenzao (Trousseau), Garnacha Tintorera (Alicante Bouschet), Brancellao, Caiño, and Sousón. In Ribeira Sacra, we make only red wines, but we do have old vineyards planted with a small percentage of white varieties. In Almansa, we work with Garnacha Tintorera. In Manchuela, we work with Moravia Agria. In Tenerife, we have never had phylloxera, so we have very old vineyards and everything is ungrafted. [We work with] Listán Prieto, Listán Negro, Negramoll, Listán Gaucho, and Malvasia Negra. For whites, Listán Blanco, Verdello, Forastera, Marmajuelo, Malvasia, Vijariego Blanco, Gual (Albillo), Albillo Criollo, and Torrontés.
Vanya Cullen: We work with two sites, 20 hectares and 30 hectares. Both have a Mediterranean climate. The soils are gravelly loam, loam, and sandy loam over clay. The varieties include Chardonnay, Chenin, Semillón, Sauvignon Blanc, Cabernet Sauvignon, Merlot, Malbec, Cabernet Franc, [and] Petit Verdot.
Kelli: Do you farm in any specific way, i.e., conventional, sustainable, organic, biodynamic?
Pete: We farm all of the ways listed, including certified biodynamic. About 30% of the acres are farmed organically. These decisions about farming are made with the winery and are based on their desires for the property. Included in the biodynamic vineyards are blackout days, which means we don’t have employees in the field on those days. This is determined by the biodynamic calendar. In many cases, we work with a vineyard consultant, who gives direction on what they would like to see
Martin: So far, we have been working in a sustainable way, no organic certification. This year, we are starting to move into organic cultivation in some of the vineyards.
Mimi: My farm is certified organic, because I believe that accountability for not using systemic and synthetic chemistries is important. While I use several of the biodynamic preps, I diverge a little in philosophy particularly with respect to tillage, which I do not practice. I have a very strong philosophy about building soil that is not compatible with repeated cultivation, plowing, etc., so while I like some of what I have taken from biodynamics, I especially like to be adventurous with compost and teas and don’t like prescriptions, so I’m constantly tweaking what I do based on what I observe. I’m trying to facilitate the recovery of lost layers of a very complex and interconnected system, providing food, forage, and safe harbor for members of the food web that agriculture tends to view as the enemy.
Roberto: For us, [it] is very important to have grapes that allow us to make a wine that shows the personality of the soil, the character of the year, and the soul of the people who cultivate the grapes. For those reasons, the vineyards and how we farm them are the most important things. We don’t believe in any “religion” or fashion; we just farm with common sense. We have learned and still keep learning that each vineyard is different, and how it has been treated is very important. For us, the most important thing is to have living soils, so we never use herbicides, and we sometimes farm organically and will use some biodynamic products. We work in this way because we believe in it and see the results. We don’t need to have a certificate for marketing!
Vanya: [Our sites are] certified organic and biodynamic.
Kelli: What is your general approach to cover crop? How do you choose which plants to grow? Do you cultivate every row? Do you mow or plow, and if so, when? What are your reasons for this?
Pete: Lots of covers crops with lots of seed choices. We use about 10 mixes. In some cases, we want to increase soil health, so we plant large biomass covers such as beans, peas, and vetch. We try to till right after mowing (same day) to get the maximum effect from the cover. We also use some perennial grasses, such as rye and Blando brome, where we want to dry out the soils. In the ideal world, we grow cover crop under the vines as well and only do a small amount of shovel work around the vines. Studies have shown this is the best way to get soil biodiversity.
We do all mowing and cultivation options listed and probably some that aren’t listed. This is all determined by what we are trying to do with the fruit. Low soil moisture areas get mowed and disked to reduce weed competition for water. High vigor areas in the middle of the valley or on the coast are only mowed. We also spade in cover crop instead of disking. This pushes the cover much deeper into the soil and helps soil health. We alternate between spading and disking by year to reduce the threat of soil compaction. Disking penetrates 6 to 8 inches into the soil, while spaders reach 10 to 12 inches. We also have some vineyards with very close row spacing (five feet) that we rip every other year. Generally, we rip to 18 inches to break up the tractor compaction next to vines.
This year, we harvested native mustard seed from one vineyard to mix with the cover crop to encourage more mustard growth in the spring. We prefer this to acquiring commercial mustard seed to grow.
Martin: We think cover crop is a really powerful tool to improve soil structure. The soils in Mendoza are very poor in organic material, so every living plant growing on them will improve the microbial activity, the cycles of nutrients, and the release of organic compounds. But, overall, cover crops are biological plows. They help to avoid soil compaction, which is one of the worst problems in soil conservation.
As we can’t irrigate them, we need to choose species that don’t need too much water. In our experience, rye seems to be the best option for drip irrigation, or a mix of rye and vetch if we expect the season to be rainy. We normally cultivate alternative rows, and we don’t disk it into the soil. We just slash it and leave it as a coverage on the soil. The reason we do that in our area is the frost risk during springtime. If we move the soil with disks, we will disturb the surface of the soil, and the loss of heat by soil radiation during nights will be too much. The only way to avoid that is to flood the soil after disking it. But, unfortunately, we cannot do that in our vineyards in Uco (because of the soil slope and drip irrigation). So, really, we are taking advantage of the roots of cover crops rather than their aerial mass.
Mimi: I do not cultivate, and I have very strong feelings about any type of agriculture that insists that it can practice “sustainable cultivation” indefinitely. Bare soils lose carbon, oxidize humus, and thereby lose biology. Period. You cannot build soil without plants. Period. My approach to cover crop is to have as many species growing during as many days of the year as possible. Plants send anywhere from 20 to 60% of the products for photosynthesis into the soil to feed the microorganisms that do the real job of feeding plants. Plants only get carbon, hydrogen, and oxygen through photosynthesis. Everything else they need has to come via a microbial bridge or microbial pathway. These organisms take inorganic forms of minerals and convert them into organic forms that the plant can absorb. The higher the diversity of plant species you have growing, the greater your microbial diversity will be, empirically, because plants have coevolved with their own species of microorganisms that assist them in their “digestion.”
I have a no-till drill that I use to add as many new species of seed as I can afford every fall. I believe in having a mix of perennials and annuals, lots of flowering forbs and herbs, nitrogen fixers, and even more tender, edible species growing all together. We do have to keep adding, as perennials tend to get the upper hand if you try to let everything reseed naturally. I’m looking for hundreds of species, with as close to year-round green as possible. If the grapes seem to be struggling, I will adjust the seed mix to try to facilitate late-season nutrient cycling. It is my opinion, and I know it is not a popular one, that if agriculture is not able to build topsoil, protect and recharge the watershed, and store carbon in a given area, then it is not suitable to that environment. In other words, if it cannot be done regeneratively, then it is not sustainable.
Roberto: Cover crop is a natural tool for balance in the vineyard. In places like in Almansa or Manchuela, where it is dry, cover crop is not good for the vines because the water competition will stress the vines. But in places like Ribeira Sacra and in Tenerife, we work with cover crops, depending [on] the year and the area. We always let them grow naturally, and we let them cover all the surface of the vineyard.
In Ribeira Sacra in a normal year, we plow by hand two times (February and July). If the year is dry, we plow three times and don’t let the cover crop [get] too tall. If the year is rainy, we plow once or not at all, and we mow to keep the cover crop from getting too tall.
[In Tenerife,] we plow deeply and by hand in Taganana. We plow three times (January, April, and July) and we never mow. Though this area is very close to the sea, if the humidity and the rain [are] lacking, too much cover crop will cause the vines to suffer. In La Orotava, we mow throughout the year to keep the grasses short, and plow every three years so that the soil doesn’t get too compacted. Because we use the traditional cordon trenzado system, the vines are vigorous, and the grasses help balance the vigor. Santiago del Teide is a high elevation site that is not as windy. Because it is drier than our other areas, we plow once in March and then mow in June. In our vineyards that are covered with volcanic ash, the grass won’t grow, and we don’t do anything to the soil.
Vanya: We utilize cover cropping to help feed the soil, maintain and improve soil structure, improve soil mineral availability, and add diversity to the system. Species are selected according to budget and availability. We select a diverse multispecies to create a polyculture: cereals, grasses, legumes, medics, brassicas. Depending on the site, we may rotate every second row to cover cropping, while in some vineyards every row is planted. Cover crops are slashed at desired times, multiple times over the growing season, depending on seasonal conditions. This cycles nutrients, feeds the soil microflora, and leaves protection on the soil over summer months.
Kelli: How important is it to have “living soils”? What are you looking for in terms of vegetable, animal, fungal, insect, and bacterial life? How do you measure these things and what do you do to encourage or control certain populations?
Pete: My personal view is there isn’t a lot I can do in the short term to impact soil health. I can screw it up pretty fast but can’t make dramatic improvements in three years. You really need 10 years of careful management to improve soil health. Healthy soils can improve water infiltration and create more uniform vine vigor. I don’t believe in using small amounts of compost (5 tons per acre). Generally, we like to put at least 25 tons per acre. Compost source is also very important. A good mix of manure, food scraps, and very well-ground yard waste is a nice mix. You have to be careful with yard waste, however, as it may have been treated with lots of commercial fertilizers. If not prepared properly, you can end up with a lot of viable weed seeds in your compost that you never wanted. We have done work with soil scientists to measure soil health. In general, we use the old farmer method, which is to simply ask ourselves, how does the soil feel and how do the vines grow?
Martin: Having living soils is key to sustaining any crop production. Soil is not just a physical substratum. In places like Mendoza, under desert conditions, we need to improve the activity of the microorganisms as much as we can during the whole season. Our soil pH is close to 7 or 8, so phosphorus and iron availability is naturally low. We really need the bacteria to do the hard work keeping the root area at a comfortable pH and full of nutrients. There is no chemical fertilizer that’s able to do that, no matter how much you use.
About measuring microbial populations, we’ve done some research on that, but the numbers are so high that conclusions are not easy to reach. And it’s not only a matter of quantity but of interaction between different groups of microbes (bacteria, fungus, etc.). What do we do to encourage those populations? We keep the soil moist enough during winter, we add liquid compost through the drippers, we add compost as mulch on the rows (under the drip lines) so that the nutrients and microbium can leach down. We also use bioreactors to multiply specific beneficial species (for example, Trichoderma), and then we inject them through the irrigation system. Everything helps, but it’s a lot of work made of little steps day after day.
Mimi: Nothing is more important than having living soils. I’m looking for diversity. I’m looking for a complete and unchallenged food web, from protists to apex predators. Habitat is how we affect that. You cannot buy soil predators or biological controls that will function efficiently and provide enough resilience to the system to do the work a farm needs to do, now and in the future. We have to recognize that habitat is the invitation to those layers to come back on their own, to bring new and diverse genetics to build exponential complexity toward an energetic system that can protect itself.
I do a lot of diversity surveys. When I see a rare species in increasing numbers, be that a beetle, a weasel, a falcon, or a lily, nothing gets me more excited. I don’t believe in wars against species. When I see a plant becoming a bully, or taking over, I see that as a sign we need more diversity. “Weeds” often tell you which of your nutrient cycles are out of balance. Bully plants often take purchase where disturbance is regular, cycles have been interrupted, so your more sensitive species cannot thrive there. We go after those species, like Himalayan blackberry and thistles, once a year to keep populations reasonable, and continue to build diversity, and over time, we have had to “fight” them less and less. I don’t believe in eradication. I think it is absurd. We are the OG invasive species.
Roberto: We think that if you don’t have living soils, you cannot have a wine with personality. Having all kinds of microorganisms makes a balance in the vineyard and healthy vines. The problem is that if you kill the environment and therefore most of the microorganisms, there is not a balance and the vines get more vulnerable to diseases. We don’t measure these things in a scientific way; we just observe them by walking the vineyard. It is easy to see and feel if a soil is alive or dead. We try to respect the environment and never use synthetic chemistry products.
Vanya: Living soils are very important to us. We are looking for diversity of life and balanced soils, which includes balanced ratios of soil microflora and what we are trying to achieve. Observation of soils and soil analysis for microbial numbers are carried out.
Kelli: Are there fundamental differences to farming mountain versus valley floor sites? Slopes versus flats? Are there things you can do on flat land that you can’t do on slopes, for example?
Pete: Very different. The valley floor is very forgiving. In many cases, these vineyards can be dry-farmed once they are established. Hillsides have much more soil variability, and as a result, you need to be on your toes. You really need to spend time walking hillside vineyards and responding. We may cultivate portions of rows or may change cover crop going down the rows to encourage more vigor. We also tend to harvest these sub-blocks separately. Keep in mind that any vineyard planted in Napa after 1991 on slopes over 5% must have a winter cover crop planted on it by October if it was cultivated during the season. The cover crop must have straw mulch spread over the top. This is all to reduce the run-off of winter rains.
Martin: We have no experience in farming on slopes or hills, because there are not too many in Mendoza. Today, 99.9% of our vineyards are on flat areas.
Mimi: The main difference tends to be depth of soil, with steep slopes being generally very shallow, flats and benches and valley floors being deeper, as that’s where the eroded slopes drain to, and the floodplains are there. Generally, those deep, moist soils tend to be much more vigorous and have the potential to hold more water, which can create a very vegetative situation for grapevines. That being said, the floor soils are being more and more cultivated for grapes for volume, and they can be almost entirely farmed with machines. Hillsides necessitate hand-farming and harvesting. Flat lands also are more frost prone, whereas the slopes drain that cold air down into the valleys.
Roberto: There are big differences. When you are in mountains, you have to look out for erosion, so sometimes you need to make terraces. Another important thing is the influence of the rain. When you are in a valley, the water from the rain is generally the same in all areas. In the mountains, the water runs down the hillsides, so it is important to work the soils to retain the water.
Vanya: There are fundamental differences to farming slopes and flats. Soil types vary, as do drainage and the expression of that site dependent on aspect.
Kelli: Do you measure the mineral content of the soils? Which ones are you looking for, and what are the desired ranges? Do you correct for mineral deficiencies, and if so, how?
Pete: Any new vineyard planting we do, we have an outside soil scientist dig pits and perform soil analysis. Pits are dug down to six feet to determine the geology of the site. This helps us determine rootstock, spacing, and pre-planting soil needs. We generally do three to four soil pits per acre. Once the vines are planted, we take petioles, or the stem of the leaf, from each block or sub-block if we have concerns about a particular area and have them analyzed to determine nutrient status. This is done post-bloom and at coloring. We then plan next year’s fertility based on what we see.
Martin: We take samples every winter, and we measure mainly nitrogen, phosphorus, and potassium. We also measure the levels of the vine leaves during flowering, to be able to calculate the output of nutrients with our crop. We replenish the levels with fertilizers in three applications: one after harvest (if possible), and the rest between budbreak and when the berries are pea-sized. If we discover any specific mineral deficiency (for example, magnesium in some Cabernet Sauvignon parcels), we try to fix it with leaf fertilization. But that is really unusual. For those areas where we see big problems of lack of vigor, or really poor soils, besides fertilization, we add compost (20 to 40 tons per hectare) and we drip liquid compost into the soil.
Mimi: I generally have a soil test done when I’m new to a site. One thing that is frequently misunderstood is how minerals in the soil relate to minerals that are available for the plant. There are actually very few soils, the world around, that don’t contain enough of the required minerals for grapes or any other plant to grow, and they tend to be desert soils that are essentially inert; sand, with its silicon-oxygen conformation, has no charge, and therefore cannot bind other charged minerals or even bind to water. Sometimes things show up as “deficient” in a soil test but might actually be present. This is because soil tests merely measure how much of any given mineral is available at the given pH of the soil at that moment, [and] minerals are unavailable to plants when they are in an inorganic form. Most soils around here will test low in available boron, zinc, nitrogen, and others. Our native pHs are low, which is common in wet climates. However, those minerals are present, and—provided you build an adequate organic matter substrate that is active as far into the growing season as possible—the microbial diversity will ensure that those minerals become available when the plant needs them.
Roberto: When we have a vineyard that starts to have mineral deficiencies, we use natural compost from goats or sheep.
Vanya: We measure the mineral content of our soils, and observation is very important to understanding mineral function and what may be deficient or limiting soil function. Certain trace minerals are important—boron for example. We use a multi-pronged approach to understanding and improving soil mineral balance, which may include applying mineral rich compost and utilizing cover cropping, for example.
Kelli: Does the variety you are growing influence the way you treat the soil?
Pete: No, but the rootstock does.
Martin: Not really. Only in some blocks of high yielding varieties (such as Bonarda), so we try to not deplete the soil with cover crops.
Mimi: No. Emphatic no. Healthy soil is my responsibility, my very first responsibility.
Roberto: It depends mostly on the vigor of the variety.
Kelli: How do you handle weeds and growth under the vine? By extension, what is your opinion of Roundup and other weed killers?
Pete: We do everything. Organic and manual treatments and in some places even Roundup. Regarding Roundup, I always ask people to consider the amount of fuel we burn spraying a quart of Roundup per acre with an ATV versus how much diesel a 90-horsepower tractor will burn cultivating under each vine. I don’t have a strong opinion on what is right. I want people to understand no one is clean in their farming operations, and they need to consider the whole system, by which I mean the watershed in the valley. Again, the perfect world is letting grasses grow under vines and only mowing them.
Martin: We do use herbicides, but only in the vine rows (not all the vineyard surface). We spray at an ultra-low volume and try to manage the timing to be most efficient. Two times per season should be enough. In the vineyards, we are moving into organic cultivation; we use mechanical in-row cultivators.
I think weed killers are a tool that should be used with a great deal of responsibility and consciousness (the same with fertilizers, fungicides, etc.). In some big farms, cultivating without them can be more difficult or expensive. Trying to use them in a sustainable way is necessary if you have to. But, in general, I don’t feel really happy using glyphosate. It kills not only the weeds, but also microbial activity near the soil surface, and it pollutes the soil. Despite the risk of damaging the vines if anything goes wrong, I think we need to work harder to be more efficient with mechanical labor in order to be able to stop using herbicides.
Mimi: We initially used a weed bar under the vines to eliminate high-growing grasses and problematic thistles. We then established, and continue to reseed, low-growing ground covers like subclover, which we can pretty much get away with not managing. We have a Clemens Multi-Clean as well which we sometimes use, but only where we see taller plants wanting to grow into the fruiting wire. If you want to get the long version of my feelings on Roundup, and you have some time on your hands, here is a link to a version of a presentation I give regularly. I am not loved by many peers for taking this stance on the use of synthetics and systemics, but I cannot tolerate the abuse of these chemicals on a worldwide scale. Their uses have born our most devastating problems and plagues, in the hands of people who do not have the education, the bandwidth, or the knowledge to even know the first thing about the way these chemicals work, how they interact with other chemicals and minerals in the environment, how they affect microorganisms in the natural world, and how they gain access to and create major changes in our own physiology.
Roberto: We handle the weeds and growth under the vine by hand or brush cutter. We think Roundup and other weed killers are the worst things you can do to a vineyard, because you kill everything and you make a drug-addict vineyard.
Vanya: We manage under-vine growth of volunteer plant species mechanically, using mowing and/or minor soil disturbances targeted at certain times of year depending on species and strategy. We understand that weed killers negatively impact wine grape quality and the longevity of a vineyard, but they also negatively impact soil health and human health, and they are not allowed under organic certification. Roundup also has been shown to contain glyphosate, which causes cancer and has been found in wine.
Kelli: How do you manage or prevent soil compaction? How important is this?
Pete: Cover crops are a big part of this. While clean, tilled vineyards look nice, they aren’t best for reducing soil compaction. We look at each site at the end of the season and determine if we have compaction. If we do, we like to add 25 tons to the acre of compost, rip 18 to 24 inches, and plant a deep-rooted cover that we can spade in the next spring.
Martin: As I mentioned before, preventing soil compaction is extremely important toward having sustainable vineyards. After making a lot of mistakes with rippers (destroying roots, for example), I found that the best way is to use the cover crops. Sowing the seeds under the tracks of tractor wheels really improves their effect. And of course, we need to avoid the use of tractor transit (especially with wet soils!).
Mimi: Soil compaction is very difficult to avoid entirely when you have to use tractors. Compaction can be a particular issue here, where we have a good amount of clay, and it can form a plow pan, or a perched layer of impermeable soil that doesn’t allow for air or water to flow. We try to make as few passes with a tractor as possible; our spray program is as ambitious as it can be with only organic tools, we only mow/hedge once (or not at all in some years), and we do those jobs together. I believe in plants for mitigation of the compaction that we incur. I also don’t actively control rodents, which are the best aerators a farmer has. Maintaining the year-round cover means they are active and have food even in hot years, and I have yet to see any damage to the grapevines—and we have so many rodents. They are critical nutrient mixers, and create tilth in the soil. It is a tricky subject, and some of the people I love and respect most still cling to their cultivation/plowing, but I cannot endorse what I believe is going to be our undoing. I am speaking on the whole of farming now. Bare soil is losing carbon. Bare soil is oxidizing humus. Bare soil is lost to wind, rain, tire traffic, etc. If we cannot figure out how to maintain green on most of the soil that is currently being farmed in the US, then we are already done. With that great battery of soil that we already have, we could actually begin to reverse the trajectory of climate change within our lifetimes. We would continue to see warming, but the next two generations might actually see improvements to watersheds, to air quality, to productivity, and resilience. It’s all within reach, but it’s also very tightly tied to a very, very powerful train going the other direction.
Roberto: For us, it is very important to prevent soil compaction, as it is important to have soils that drain water and develop deeps roots. So depending [on] the texture of the soil, we plow less often where it is sandier, and the depth of the plowing depends on the age of the vines and the depth and type of topsoil (we typically plow between 10 to 15 centimeters).
Vanya: Very important. To avoid it, we minimize traffic in [the] overall management plan, target specific seasonal timing of traffic in the vineyard when less vulnerable. Building soil structure and soil balance also reduces susceptibility to compaction.
Kelli: What is your approach to irrigation? How does it relate to soil health?
Pete: That’s all dependent on vine growth. We also like to look at wines for irrigation. Studies have shown that you can manage tannins in the wines by keeping water on later in the season. We do use a lot of measurement devices to decide when and how much to irrigate. Once a vineyard is established, we like to keep the water to a minimum. We do both short irrigations (4 gallons a week every week) and long irrigations (20 gallons three times a year). It all depends on what the water-holding ability is, the rootstock type, and the goal for the site.
Martin: It’s unfair to answer this question coming from Mendoza, because we need to irrigate. We cannot think about any agriculture without irrigation, so it’s a part of our day-to-day management. What I can say about irrigation is that maybe the biggest problem is to over-irrigate, especially at the beginning of the spring. That creates an environment with low temperature and lack of oxygen in the soil, and all the microbial and root activity gets depressed. It’s mandatory to monitor the moisture levels and to be able to use different irrigation frequencies according to soil types.
Mimi: Water is limiting for everything. It is an undeniable truth, and we are all going to feel the weight of that more and more as the years grow hotter and drier. However, when topsoil, humus, microorganisms, and their protection are your priority, the soil can naturally hold many times its own weight in water. Soils with high organic matter and humus are wetter, longer. Moreover, roots (from cover crop plants) continue to hold water, to feed microorganisms, and create a more stable environment for grapevine roots to make use of throughout a droughty season.
Roberto: We don’t think irrigation is bad when it is without chemicals (only water). In the places that we work, we don’t need to irrigate, but we understand that in some very dry places you need to give water to keep the vine working. The problem is when you irrigate for quantity and you use too much water; this can affect the soil negatively and vines will develop roots on the surface.
Vanya: No irrigation is used in established, yielding vineyards. [It’s] not directly related to soil health.
Kelli: Do you use fertilizer or compost? If so, how and when do you apply it to the vineyard? How do you determine what to use?
Pete: We use compost and organic and conventional fertilizers. Generally, we like to inject our fertilizers via the drip system when we irrigate. Vines need very little as compared to other crops. This is determined by observation and petiole reports.
Martin: We use fertilizer as a base to replenish the soil after mineral extraction, and we use compost for fixing the tricky places. Using compost is expensive and complicated, so we need to make a plan every year to set priorities. We study the evolution of pruning weight in the parcels to detect decreasing vigor. We apply it in winters, as a surface mulch, and via the drip line. We don’t disk it into the soil.
Mimi: I do not use fertilizers. Plants are in a dynamic relationship with their environment that is informed, in real time, by the conditions of a particular moment. Plant metabolism dictates when certain micronutrients or cofactors are needed in tiny amounts to catalyze the reactions that drive all processes of plant function. We do that very clumsily, at best, when we dose in micronutrients, and we interrupt the process of the plant gaining access to those things through the soil. Here at Hope Well, our main way of creating new organic matter and topsoil is using year-round cover, which decomposes during the year to return nutrients to the soil. We use compost mainly to make compost teas, which are applied both to leaves and to soil. This is less about nutrition than it is about encouraging microbiological diversity.
Roberto: We use compost from goats or sheep, which we apply during winter with a plow.
Vanya: Yes, compost is used [and] customized mineral fertilizer may be used. We determine this based on observation of the vineyards as well as soil testing, tissue testing, and microbial testing. Applications are generally made in autumn and/or spring depending on what we are trying to achieve, using specialized spreading equipment.
Kelli: In your experience, how does soil health specifically relate to wine quality?
Pete: If you have nutritional issues in the vineyard, such as low nitrogen, you will have issues in your fermentation. More food will have to be added to fermentation to keep it active. In general, our best wines come from our less vigorous (less healthy) soils—note I said less healthy not least healthy. Big, deep, rich soils are great for growing corn but not for growing great wines.
Martin: I strongly believe that a great wine cannot be made with grapes growing in sick or poor soil. We want the vines to be balanced and happy, with a good canopy, healthy shoots and leaves, and a good capacity to take nutrients and minerals from the soil and to ripen the fruit properly. Both lack and excess of vigor are a problem. I think that a soil with a good amount of organic material, a great deal of microbial activity, a good balance between air and water, and with no compaction is the perfect start for a healthy vine, quality canopy, and, finally, quality bunches. I think the complexity of the wine improves when grown in healthy soils. The mineral texture and the balance of sugar and acidity is also improved.
Mimi: The wines that inspire me, and the wines that I hope to grow, reflect the exponential unfolding of energetic relationships between the vines and the most diverse environment I can encourage and support. The greater the diversity of plants we have here, the greater diversity of all life, leads to a greater potential energy in the wine. The minerals that support the synthesis of complex molecules in wine are a minuscule fraction of what constitutes nutrition for the grapevine, but they are arguably where all the most important detail comes from in wine. The finest expression of place is a mind-blowingly complex series of conversations of a plant with its environment, and reducing that environment—by eliminating competition, by attempting to eliminate all other plant and animal life, by changing the vine’s intuitive relationship to one of dependence on a human to provide water and nutrients—breaks down the web of stability. I don’t believe great wine can be made this way, but more importantly, we cannot hope to do this in perpetuity. The landscape will not support the creation of great wines if we do not support the landscape.
Roberto: We think that the personality of the wine is given by the soil, so if you have a dead soil you will have a wine without personality, boring. For us, this is a wine without quality. For this reason, [we] try to study more and more the soil in each vineyard. When we work them with respect, we have a wine with personality!
Vanya: [Soil health] contributes to mineral availability and uptake, balanced vine growth, and balanced wine grapes, [influencing] expression of variety, site, and the micro- and macroclimates where they are grown.
This is fantastic! Thank you very much for such wonderful content.