This innovative trial explores a variety of test plots of native grasses to solve water issues.

See the post as God intended (with photos, etc.) on free substack post.

A Long Term Relationship

Mankind has been “managing” weeds for more than 5,000 years, and hasn’t found the perfect system in crops or vineyards yet, but the latest frontier in researching ground cover for wine growers is taking an unexpectedly rigorous turn at Opus One with the help of Selena Vengco, biologist and native plant specialist at U.C. Cooperative Extension and veteran agro-ecologist Dave Kaplow (of Eco-Management in Santa Rosa).

Kaplow’s approach stands in contrast to regenerative organic cover crop initiatives that focus on quick start biodiversity, planting seed mixes with as many as 28 species in a vineyard.

Kaplow says his approach, though slower to take root, is road tested and built for the long haul.

Opus One assistant winemaker and viticulturist Kimberlee Marinelli shared the innovative trial on ground cover with a crowd of about 30 people attending the third field day July 22 in a forward-thinking series on organic wine growing education (under the leadership of the Napa Valley Grapegrowers) during their “organic month” series in July.

A New Estate Vineyard | Ground Cover Trial Site

Vengco and Kaplow worked with the Opus One team as the winery takes on a newly acquired, 33 acre Oakville vineyard (the former Stanton vineyard) along the Napa River.

See the post as God intended (with photos, etc.) on free substack post.

Kimberlee Marinelli photo

“Opus One purchased it in early 2025 so this is kind of our first couple of years really understanding this property,” said Marinelli. “A big thing that we’ve been doing at Opus One is questioning all of our viticultural practices, really thinking about how stewardship is at the crux of what we do.”

Farmed organically since 2011, she said, the estate was certified in 2022.

In 2022, the team heard from Mimi Casteel at a Napa Rise event talking about regenerative farming practices and how do wine growers really make an impact with a changing climate.

“She talked about a lot about hydrology and how on the hillsides there’s such great opportunities for larger micro and then macro climate cooling. So this got our gears turning about thinking about hydrology, when we think about vineyard redevelopment,” Marinelli said.

The estate winery is moving toward regenerative organic practices (and potential ROC certification).

“We have since transitioned 60-65% of our vineyard over to perennial cover crop. It’s not all grasses,” she said. “We have different mixes depending on the goals all over the estate. But here…the plan is to have this area fallow for hopefully a few years to have some time to understand the property.”

A Unique Site | A River Runs By It

Like many others in Napa Valley’s central corridor, the site has a really high water table along the river.

“That is a blessing in the drought conditions that we have,” she said, “but it also can be a challenge. So we really have to think about managing that….it’s a biodiversity hotspot, and a riparian zone…This was a floodplain, and so we really want to honor that when we think about how we’re going to approach redevelopment on this parcel.”

Enter Oregon born, agroecologist Mimi Casteel, a well known champion of vineyards and biodiversity, who consulted for the winery and challenged them to consider options.

Mimi Casteel speaking at Napa Rise in 2023 See the post with photos, etc.) on substack free

“We had done soil pits and talked about the high water table…It was August, and we were hitting water at 456, feet, and having standing water. So there was a lot of water here, especially as you get to the back of the property [by the river],” Marinelli said.

“There’s obviously some active hydrology happening here, and when Mimi came to the property with the team..and we love Mimi because she really does not hold back at all…[and her comments were] ‘How are you going to develop this?’”

Experimenting with a New Agroecological Approach | Can Plants Mitigate the Hydrological Challenges?

“We’re doing so much to promote agroecology,” said Marinelli, “… And she was kind of challenging us, pushing us. ‘How are you going to plant vineyards all the way up to the riparian zone? Does a vineyard really need to be there?’”

“From this challenge came a lot of curiosity, and from that friction came this trial. So that is how we connected with Dave Kaplow,” she said.

The vineyard could lie fallow for some period of time which gave the team time to do research.

“We’v go some sediment, but then we’ve got some clay and sandy soils and higher clay as we get towards the river,” she said.

French drains and drain tiles were options. But the Opus team pivoted to a new approach.

“Potentially grasses could help fluctuate some of the water table…or help absorb so that vines could coexist without having to use some super invasive vineyard development techniques,” she said. “From that, this grass trial was born.”

Embarking on an Innovative Native Grasses Trial

Missing photo See the photos, etc. as God intended on free on substack.

With Kaplow’s knowledge of native grasses from years of working in conservation and on golf courses, the team set about creating a field trial with a variety of Kaplow’s recommended grasses.

Vengco brought her research skills to the project.

First, the site was treated with biochar and compost (at a rate of 10 tons an acre), spread throughout the fallowed field, then disked in, smoothed out, and ring rolled. The team then marked out a grid with the different strips for the trial.

Kaplow recommended five grasses and two combinations to try.

Planting the Seeds | Not As Simple As It Sounds

“The biggest challenge in seeding was the different sizes of the seeds. The Diego bentgrass, for example, has seeds that are really, really fine, almost like a dust or powder,” said David McGraw, production manager at Silverado Farming. “So they just slipped right through the seeder. We had to mix them with rice hulls and organic granular fertilizer to bulk up the volume, and then we were able to seed that at a better rate.

“Calibration probably took the most time and was the most critical part,” he said. “A lot of these native seeds are small productions, so they’re quite expensive. So we really wanted to make sure we didn’t overseed and run out because purchasing more was not an option. So we would seed, calibrate the seeder for each seed, seed all of it, the different strips all the way down. Once that was finished, we’d switch to the next seed, recalibrate, and repeat the process seven times.”

By the time it all was seeded, they lucked out with some nice rain that came in and germinated everything. “And from there, we just let Mother Nature take over,” said McGraw.

Preliminary Establishment Results

Researcher Vengco’s reported on how quickly the native seeds responded in the first year.

The first year results are published here. See the post as God intended (with photos, etc.) free on substack.

An Ecological Approach to Grasses

As background, Kaplow said, “The work I did from the beginning had to do with native grasses, so I was learning all about native grasses and how to manage native prairies, and that’s my orientation coming into looking at a vineyard ground cover.

“I’m looking at from the perspective as an ecologist, and how are the maintenance techniques or the seed selections affecting what the ground cover does, and how does it behave? So I have learned from all these years.”

“My preferred ground cover is working with perennial grasses, particularly natives, and from there I can enhance onto using wildflowers and perennials and all the other things. But I always start with grasses first.”

Why Grasses?

Kaplow recommends native perennial grasses over annuals.

“They have certain major advantages over the annuals that you're using. When you look at the grasses, you're going to see foliage even in the height of the growing season. They may only get six inches tall if you didn't mow them. They don't get tall. They're little bunch grasses, but underground, they're putting roots that are going down five or six feet, and they're putting a lot of carbon into the ground.

“Around the world, it's well known that the soils with the highest amount of soil carbon are all grassland soils. They're all prairie soils. So, in a sense, what I'm talking about doing here is putting in strips of linear prairie into your vineyards.”

Carbon Sequestration and Microbiome Advantages of Native Perennial Grasses

“If you want to put the carbon in the ground, you have to let the roots do it,” Kaplow said.

Kaplow said the native grasses inject a lot of carbon into the soil and create a stable environment for the beneficial bacteria and fungi to grow. “Versus, if you have annuals, their roots only go down about a foot, and they’re going to die at the end of the season,” he added. “So you’re kind of starting from zero again for the microbial community, or at least their habitat is pretty much starting from zero. Whereas with perennials, you have a stable environment, and you can get the microbes to grow much better.

“Perennial grasses are very good for mycorrhizal association, bacterial association. So if you’re trying to get soil microchlora, perennial grasses are a great way to go.”

Native Grass Establishment: "Like Prepping a Canvas”

Kaplow said he loves wildflowers but recommends waiting until the native grasses are established before planting them.

“The first step you're trying to do in a perennial cover,” he said, “is get a stable background. It's almost like prepping a canvas. You're trying to get a stable surface that's going to be weed resistant, and as the perennial grasses grow, their roots are going to fill the soil, and they're going to basically make a wall of roots. And when weeds try to germinate in that; their roots are going to hit the native grass roots, and they're going to stop.”

He is not an advocate for planting legumes as cover crop for nitrogen. “If you don’t need the nitrogen, don’t put the legumes in, because they’re going to harbor a lot of pests. Too much nitrogen in the soil creates a weed problem. If you don’t need the nitrogen, don’t do it. If you do need the nitrogen, absolutely, that’s not a question. But if you don’t need it, don’t do it,” he said.

Kaplow cautioned against using fescues and and bluegrasses. “I didn't use any fescue or bluegrass in this project, and the reason is that I've worked with them in restoration projects a lot, and fescue and bluegrass are northern grasses. They're moist site grasses. If you are in Washington State, it's a no-brainer. If you're in British Columbia, absolutely.

“There are native fescues and bluegrasses here, but they're on the north side of a hill. They're in the shade of trees. They're in the fog belt next to the ocean.

“You don't see them wild out here. You can seed it, and you will get scattered plants. But you're not going to get reliable results. You're not going to get a full cover. It certainly won't live. So that's the only reason I didn't try those.”

See the post as God intended (with photos, etc.) on free substack post.

Diego bentgrass photo

Seeding Is A Bit of An Art Form

McGraw cautioned, “With native grass seeding you really have to be careful. The seeding rates are so low. You say, ‘Oh, I bought seed for five acres,’ and you use it up after one, because ‘it just doesn't look right.’ You seed it, and you don't you don't really see anything, and you go, ‘I’ve got to put more. Well, by the time you did, you've overseeded. So you really have to learn to stretch it out.

“Sometimes what people do is they will mix it with rice hulls, or they'll mix it in with something else to spread it out, so that it looks better…It's as light as humanly possible, and even then, you’re probably putting it on too heavy. So that's a major case of self-control.”

The rest of the morning was devoted to looking at each grass plot.

Kaplow said that even after just one year, some of the grasses, which were only about an inch high, would have roots extending three feet deep.

“They’re reaching for water. They’re trying to make it through the summer. Now eventually they’re going to be six, eight feet deep. They’re going to hit the water table at some point. Maybe they have, but I don’t know. They’re still young.

“Eventually they’re going to not only grow down but sideways, and the root systems can start banging into each other. So it’s going to become a wall of roots…each year it gets a little more like that.

California oatgrass (Danthonia californica) is old-growth grass in California is a long-lived native perennial bunchgrass that can live for up to 200 years and helps sustain ancient meadow ecosystems.

“Danthonia has a very, very long term strategy,” said Kaplow. “This grass, when it’s going, will live 120 years. It would be an old growth kind of grass. This is the redwoods of the grasses, but it’s hard to start it.

“I'm not quite giving up on it for here because that is one that will stay green and will dry this field out if that's what you need,” Kaplow said. “It's long lived and once it's in, it's in forever. It's just a great plant. I have high future hopes for it. I've got this growing in my front yard in Santa Rosa. I don't water it and it's still green.”

This is part one of a two part article. We will post a link to Part 2 here soon.

The final event in the NVGG organic series on July 29 featured a keynote conversation featuring two respected organic producers-Steve Matthiasson of Matthiasson Wines and Jason Haas of Tablas Creek Vineyard.

That will be the subject of a future post here.

Wine Country Geographic

Message History

Delivery option(s)