Growing & Winemaking


Native Plants Offer Cover, Too

February 2011
by Peter Mitham
cover crop wildflowers
With the help of the Washington State University extension office, viticulturist Jason Schlagel of Ste. Michelle Wine Estates chose a mix of local grasses and flowers to create beneficial diversity around Columbia Crest Estate.
Vitis vinifera may not be a type of weed, but it would be deemed an alien invasive species if it was let loose today. Its domestication and cultivation in North America is a great thing, but too often its economic benefits leave little room for growers to consider its impact on the native ecosystems vinifera is occupying.

Ironically, accreditation systems like Lodi Rules and LEED (Leadership in Energy and Environmental Design) give points for vineyards and wineries that respect the local environment, preserving and encouraging native biodiversity as well as water-efficient landscaping.

Ways to achieve biodiversity include setting aside tracts of land for native habitat and planting land outside and inside the vineyard with native species. While there’s often an aesthetic appeal to creating a native landscape around a vineyard, native plants also can boost populations of beneficial insects and provide a natural means of enhancing soil health within the vineyard.

A mix of native grasses, mustards or legumes that match local growing conditions is especially helpful in building soil organic matter. Cover crops are a relatively safe option for achieving this because, unlike composts and other amendments, there’s little risk of introducing pests and other troubles into the vineyard.

Organic matter matters

“The most cost-effective organic matter is organic matter grown in place as a cover crop,” said Stan Grant, owner of Progressive Viticulture in Turlock, Calif., and a former viticulturist for Gallo Vineyards. “Soils that are well supplied in organic matter tend to support larger, more diverse populations of soil inhabitants, and under these conditions the ability of any particular inhabitants—nematodes, phylloxera, for instance—to damage roots is more restricted.”

Deep-rooted cover crops also may help draw nutrients closer to the surface and vine roots, making them available following decomposition. And leguminous plants such as beans, peas and clovers, which fix atmospheric nitrogen, make their own contribution as part of the mix.

Grant explained that annual cover crops are ideal for vineyards, where the regular replenishment of soil nutrients is key to offset the regular depletion that occurs with each year’s crop of fruit—the single biggest cause of vineyard nutrient loss. Vineyards with divided canopies, which maximize crop density, are particularly vulnerable to nutrient depletion.

Among the species native to California that have been successfully used as cover crops are Blando brome, Zorro fescue, purple vetch and certain clovers. Grant has little experience with most of these plants other than in trials, noting that expense and soil management objectives typically place mixes of other mainstream seeds at an advantage in commercial settings.

“Native cover crop seed is expensive, and domesticated cover crop plants are often better suited to meet specific soil management objectives,” he said.

Arid Northwest environments
Outside California, in the arid environments of British Columbia’s Okanagan Valley and the high desert of Eastern Washington, wheatgrasses and other drought-hardy species are what farm advisor and Wines & Vines columnist Glenn McGourty recommends.

Some perennial cover crops can slough off about half their roots each year, returning nutrients directly into the soil (about 1.6 tons per year on average for a conventional vineyard).

McGourty recommends some of the old ranchland standbys such as crested wheatgrass or Siberian and streambank wheatgrass (sodar) to help stabilize the vineyard floor. He also recommends a mix of grasses and legumes, because the two complement each other in terms of nutrients returned to the soil, and conditions change from year to year. He estimates the cost of establishing an effective cover crop system at $50 to $500 per acre.

But native species offer an alternative to conventional seed mixes. Working with Jim Holmes of Ancora Estate in Washington state’s Red Mountain AVA, Dr. Steven Link of Native Plant Landscaping and Restoration LLC in West Richland, Wash., has been investigating the potential of native nitrogen-fixing plants such as silky lupine and antelope bitterbrush as vineyard cover crops. The plants serve the same purpose as traditional cover crop mixes but lend a natural diversity to the vineyard and are typically more efficient in their use of resources such as water.

“Classical cover crops, classical wheatgrasses and crested wheatgrass—which is in Jim’s field—are a very old-fashioned idea in my personal opinion,” Link said. “They’re easy and cheap, so they’ve taken over. I think there are reasons, and good reasons to look for alternatives.”
Native buzz in WSU vineyard research

Boosting habitat for beneficial insects is one of the ancillary benefits of having a native cover crop. By featuring native plants, vineyards can host indigenous insects that will enhance biodiversity and often find feeding opportunities among vineyard pests.

These include pollinators such as clearwing flies as well as parasitoids that attack caterpillars and worms. Various Anagrus species are helpful in the control of leafhoppers and vine mealybug. A few of the spiders helpful in leafhopper control are attracted by the grasses included in some cover crop mixes. Evidence indicates that mallow may help control cutworm by being an attractive but toxic food source for larvae of the pest.

The benefits of native species are the subject of a three-year project that Dr. David James, an associate entomologist and extension speci alist at Washington State University-Prosser, is launching in collaboration with other WSU researchers. Plots of native plants at four vineyards in Eastern Washington will recreate patches of the local sage steppe native to the region with the aim of creating habitat for pollinator bees, butterflies and other threatened but beneficial insects.

“The project will address the Washington winegrape industry priorities of reducing synthetic chemical inputs, improving integrated pest management and implementing sustainable farming practices that protect the environment and community as a whole,” the project’s abstract states.

Perennials identified for potential establishment include coyote mints and other native herbs, yarrow, nettles, rabbitbrush and penstemon.

James hopes to evaluate the perennials for practicality as cover crops as well as the ability to attract and host beneficial insects. He also hopes to evaluate populations in conventional vineyards and those with restored habitat as well as engage with growers to enhance knowledge of integrated pest management systems.

Local beneficial insects

Plant biodiversity is one reason, as is the creation of habitat for local beneficial insects that might not be as attracted to cover crop mixes that meet viticultural purposes alone. “That adds something of value to the system,” Link said. “I don’t find too many people opposed to it; it’s more a matter of trying to do it because people don’t do it very commonly at all.”

And small wonder: In lieu of widely available commercial supplies (many native grasses are available, but native nitrogen-fixing plants are less common from commercial sources), Link gathered the seeds he needed by hand in 2008 from a seven-mile radius around Red Mountain. He then took time to germinate the seeds prior to planting seedlings (plugs) in spring 2009.

The initial results indicate that forbs such as silky lupine and local milkvetches (Astragalus species) could become established but should be planted before grasses, which are highly competitive. Indeed, even existing grasses made establishment difficult for the plugs Link placed in the vine rows to establish.

“I would stay away from the grasses until you can get some forbs into the system,” Link said. “Grasses are very competitive. So if you wanted to establish a diverse mix of native species for a vineyard, you would probably be wise to put the grasses in later, in smaller amounts.”

The competitive influence of grasses is also seen on vines, where competition for nutrients may help control vine vigor in some areas but hamper development in others. The plugs Link planted in 2009 are viable, but he began a trial in December 2010 investigating the potential to grow native legumes from seed for use as vineyard cover crops. Although seed germination isn’t guaranteed, they promise to be more efficient and less costly than plugs. The new trial planted scarified seeds at 1/8 inch to 1/ 4 inch in depth, which Link hopes will facilitate germination.

Ste. Michelle’s wildflowers
One major winery is already using native species to enhance diversity, and it’s doing so from seed—albeit commercially available wildflowers rather than grasses. The goal of the mix is to beautify the property, boost populations of beneficial insects and keep local grasses at bay.

While grasses are effective in preventing erosion, viticulturist Jason Schlagel of Ste. Michelle Wine Estates’ vineyards in the Horse Heaven Hills AVA says they’re not wanted in the vine rows because of the competitive pressure they create. (The inter-row area is held down by a perennial rye grass.)

Controlling local grasses is where native flowers such as lupine, white yarrow, Bird’s Eyes and Black Eyed Susan play a role. With the help of the Washington State University extension office, Schlagel chose a mix from the Oregon Wholesale Seed Co. in Silverton, Ore., breaking up the grassland and creating a beneficial diversity around Ste. Michelle’s Columbia Crest Estate and Canoe Ridge vineyards.

Originally planted in 2009, seed has been saved from some plots at Canoe Ridge and mixed in with new seed to reseed plots (using a basic lawn seeder on the back of an all-terrain vehicle) and reinforce plantings adjacent to vineyards. The effort seems to be paying off, though Schlagel said he doesn’t have data quantifying the results.

“Every year we’re getting stuff coming back from the previous year’s seeding, and I think we’re making steps forward to get at least the perennials coming back every year,” he said. “It’s ongoing. We haven’t seen any real hard results yet, but I think we’re improving.”

That’s not a bad summary for the relatively new subject of native plants in vineyard cover crops. With the alien species of Vitis vinifera dominating vineyard properties, it seems only fair to give natives a chance to contribute.

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