Marvelous mustard: How these golden blooms help North Bay vineyards, pastures

Drive along Petaluma Hill Road from Santa Rosa to Rohnert Park in Sonoma County and the rolling meadows to the west are shimmering with it.

Ride a bicycle through the backroads of Dry Creek Valley and the dark, gnarly zinfandel old vines contrast starkly with the yellow brilliance of it.

A tour of the Silverado Trail shows wave after wave of the uncontested harbinger of spring growing in profusion among the rows of Napa Valley’s wine estates. It’s even found in profusion between Highway 12 and Third Street as you head to Imwalle Gardens to buy vegetable starts.

It is mustard time in the North Bay.

From the end of February through March the plants grow fast and furious, serving as the backdrop for many a calendar shot or wedding portrait.

Some vineyard managers plant mustard for more than its magnificent gold and yellow hues, however. This aesthetically pleasing cover crop has supreme value as a “green manure.” When the weather warms and the mustard plants begin to set their seeds, the vineyard workers mow it down, and either let it lay where it drops or till it under to do its nourishing magic deep underground.

Mustard is planted in the fall in our region. Sometimes it will be sown to refresh a fallow field, growing an average of five to six feet, or even higher. The hardy mustard seeds can survive in the soil for up to forty years and burst into life after a late rain.

Cover crop seed mixes consisting of members of the brassica family, such as mustard and radishes, are valuable for a host of reasons.

When planted on sloped grades, they prevent erosion and decrease nutrient runoff. Mustard retains soil moisture, recycles nitrogen, reduces weeds because of its early vigor and fast growth, and attracts a variety of pollinators with its bright blooms. These attributes of the plant interest farmers and gardeners who wish to improve overall soil health, but for the health of the growing wine grapes, there is an additional benefit.

Mustard plants help suppress the nematode population — microscopic worms that can damage vines — because mustard contains high levels of natural chemical agents called biofumigants.

The best types of mustard to grow are those with high levels of Glucosinolate, the extra spicey compounds that give mustard seed that slight pungent taste and further deter the roundworms.

Examples include black mustard, ida gold mustard, oilseed radish, daikon radish and wild radish. The seeds are so hot they repel insects. Reducing these harmful organisms by natural means spares our vineyards the harm done from artificial eradicators and dangerous pesticides.

Cutting the mustard

Kelly Boyer has been working at LeBallister’s Seed and Fertilizer for nearly 20 years. A former educator with an ag business degree from California Polytechnic University, she has assumed the general manager role from her father, Tom Hendrickson, now 79.

In 1947, Hendrickson’s grandfather, George LeBallister, bought a Sebastopol apple ranch, where, in addition to packing apples, he sold agricultural chemicals and fertilizers on the side. In 1980, Hendrickson purchased his grandfather’s inventory and five years later he expanded to include seeds and seed equipment.

Today LeBallister’s sells about 50% seed and 50% fertilizer. The family-owned business specializes in creating custom seed mixes and offering consulting services from a facility located on Sebastopol Avenue in Santa Rosa.

“We have always sold mustard as a cover crop, but there has been an uptick in the last five to eight years because of interest in sustainable farming,” Boyer says.

Like home improvement stores and other agriculture-related businesses, the company has been open and consistently busy all during the pandemic.

“We sell about 95% to the vineyards, but small farms, big farms, home gardeners all want these seed mixes for prepping the ground. Mustard’s deep taproot helps break up our area’s clay soils.”

Besides being prolific and quite adept at reseeding itself, Boyer says mustard is appealing because of its price. “It’s $1.50 a pound, and you use 15-20 pounds an acre. By comparison, poppies are $15.50 per pound.”

Boyer notes that mustard wasn’t always planted as a crop to grow and sell.

“It was considered a weed, the bane of the farmer’s existence because it got in the way of the hay they were trying to grow. To them the thought of planting mustard on purpose was a little crazy.”

One winery official who asked not to be named wrote, “The majority of the mustard in our vineyard is naturally reseeded. It does indeed look beautiful, but it is essentially a prolific weed with benefits: preventing erosion, discouraging nematodes and creating fantastic backdrops for photos. We don’t consider it a highly important aspect of our wine production.”

Mustard and the vine

Whatever choices growers make in the present day, wine is a part of mustard’s heritage in that it was the “must” (freshly pressed fruit juice) from the winemaking process that was first used in making prepared mustard. Historical sources cite the use of mustard seed as a condiment mixed with the sweet must of old wine called mustum ardens, or hot must. Some of the earliest known documentation of mustard’s use dates back to Sumerian and Sanskrit texts from 3000 BC.

Dani vanDriel, on the Sask Mustard website, confirms the “ancient connection between mustard and the vine” this way: “Mustard and wine share an affinity on many levels. There is the delight of grilled chicken in mustard cream sauce paired with a crisp Chardonnay, for example. And the flagship of all mustards (Dijon, of course) is made with wine. The plants themselves—the mustard flowers and the grapevines—get along famously as well.”

Brad Hanson, extension weed specialist in the Plant Science Department at UC Davis, likes to sing the praises of cover crops, of which mustards are common components.

“Because of its root architecture, mustard is important for soil health,” Hanson said. “When its taproot decays, it leaves a channel that makes space for air and water to penetrate. Custom mixes also include plants that fix nitrogen from the atmosphere, like vetch or peas. I would say soil building is the biggest benefit of mustard and cover crops in wine production, especially in the hilly areas where it prevents erosion.”

Hanson noted that a mustard or radish cover crops also are advantageous to pollinators.

“Grapes don’t need bees and other pollinators, but the flowers are beneficial from an overall ecosystem point of view,” Hanson said. “The reason to mix different plants is that one might have an early flowering, one a later flowering, so it extends the time that the pollen is available.”

Mustard aids in weed control because it grows fast and tall, using up nutrients and water, and shading the undesirables. The timing of bud break in the vineyards and when mustard finishes flowering often coincide. But exactly when the cover crop is cut, and whether it is left on the surface or plowed under, depends on the needs of the growers.

“If they are trying to produce seed to regrow, they will wait to mow and then till it in. If these are unwanted plants, they get mowed before they set seed,” Hanson said. “In the vineyards in spring, they often cut the cover crop between the rows because it’s in the way and they need to get to work.”