Grape growers in Napa County are constantly looking for innovative ways to decrease waste while increasing productivity in their vineyards, but not all of these methods are high-tech or brand-new. For many, the act of accumulating, turning and spreading compost is a basic but key part of their vineyard management strategy, and has been practiced since ancient civilizations first prioritized agriculture.
“Composting has always been considered key to better farming and is a key practice employed in Napa Valley vineyards,” said Michael Silacci, winemaker for Opus One and president of the Napa Valley Grapegrowers. “When composting is done properly using good management techniques and temperature monitoring, the result is a fine source of nutrients for plants and it has a positive impact on preventing soil erosion by rebuilding soil structure and supporting plant growth.”
By increasing microbial activity in these waste materials – think oak leaves, grape stems, manure – pulled from their property, vintners are able to not only benefit soil health, but also keep as much of its waste on-site as possible.
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“The mission of the Napa Valley Grapegrowers is to preserve and promote Napa Valley’s world-class vineyards, [and] the watermark hovering behind this statement is to protect. Given the impact of climate change on the Napa Valley, it is imperative that we go beyond simply recycling to reusing,” said Silacci.
The actual breakdown of what vintners choose to compost varies year-to-year and vineyard-to-vineyard, but generally is a mixture of different organic plant and animal waste. According to Gustavo Avina, viticulture director of Pine Ridge Vineyards, the ratio of plant-to-animal waste directly correlates to what types of nutrients will be spread across the property, and thus differs based on growing conditions.
“For instance, grapevine-based compost can be high in potassium and some heavy manure-based types can be very high in nitrogen,” said Avina. “On the same note, poorly sourced and produced animal-based compost can be high in salts … Compost quality is the driver here, as both compost types are invaluable tools in viticulture.”
In addition to differences in material makeup, there are also different methods of spreading compost. Some vintners prefer compost teas – made by quite literally brewing a sachet of compost in water – so they can apply compost similar to irrigation, while others opt for physically spreading the solid material across the soil and incorporating it through discing or other intervention.
“For existing vineyards, I really prefer compost tea, [because] it goes straight to the root zone and it starts to work right away,” said Avina.
Since Pine Ridge started using compost tea, Avina estimates they have reduced their water use by nearly 40 percent, and the canopy of their vines have improved tremendously.
“In addition, we have also observed a dramatic improvement of how vines handle heat events,” Avina said. “The fact of the matter is that many of the vineyards we purchase from and that do not utilize tea injections have more shrivel, leaf burn, damage to exposed to clusters such as rosette or pinkish sunburn, and in some cases, canopy collapse.”
However, for developing vineyards, Avina suggests solid compost because you can add it based on the needs of the soil.
At Seavey Vineyard, Fred Seavey and the rest of his staff take this a step further by incorporating biochar into their compost. In addition to a mix of manure from the property’s goats and sheep, grape skins and downed leaves, Seavey also burns dead vines and other wood to capture carbon in the vineyard.
“Napa RCD taught us how to do the burns in a way that produces that biochar so we can recycle it into our compost and into our soil,” said Seavey. “By heating it up in the absence of oxygen, you turn all of that material into almost pure carbon, and then you can put the carbon into the soil.”
Using biochar in this way thus sequesters carbon – in turn mitigating climate impacts – as Seavey would otherwise need to ignore or burn any downed wood or dead vines on the property.
“If we were just going to leave the wood on the forest floor, eventually it would decompose and break down and return that carbon into the atmosphere as CO2,” said Seavey. “It also enhances the water holding capacity of the soil, which makes us more drought resilient, and it helps us be a place with microbial life.”
In general, while vintners use compost in slightly different ways depending on the needs of their soil, the size of the property or even rainfall, the general consensus is that reusing this waste is a benevolent act, that also just might lead to a more delicious wine.
“The more we do to isolate the inputs to a vineyard, the more authentic the reflection of place,” said Silacci. “Allowing wild yeast from the vineyard to ferment grape juice, using composted materials from the vineyard, and understanding the site all lead to a greater sense of place in wine.”
You can reach Sam Jones at 707-256-2221 and firstname.lastname@example.org.