Joseph Phelps Winery: Using Compost to Help Capture “Terroir”

Joseph Phelps Winery, Napa, California.

Winemakers manage their vineyards to cultivate particular characteristics in their wine, including flavors and aromas unique to their soils and climate, sometimes known as “terroir.” For Sarah Black, viticulturist, tending the vineyards and managing 600 tons of organic waste material each year and applying its compost for soil restoration is a full-circle labor of love for the land and the wine.

Sarah operates a compost facility at the Joseph Phelps Vineyards winery in Napa.

Located on what was once a cattle ranch on the rolling hills of the eastern slopes in Napa Valley, the winery has 120 acres planted and is home to a compost site that sits among mustards, poppies, daisies, soaring blue oak trees, and other native species that provide a habitat for birds and a host of beneficial insects.

The compost project site sits in a small valley on the property—not far from the wine tasting room and surrounded by vineyards on all sides. Feedstock for composting includes manure from an organic dairy, wood chips, and grape seeds, skins, and stems (sometimes called pomace) from winemaking. After building a windrow, the pile is turned and aerated. The windrow is about 100 feet long and 7 feet high. Sarah makes sure to meet the “time and temperature” requirements that kill weed seeds and pathogens. The windrow reaches temperatures up to—and sometimes exceeding—150 degrees Fahrenheit, more than hot enough to comply with the standards for pathogen reduction established by California regulations.

Just a short distance from the windrow pile, Sarah turns up a small shovelful of soil from along the vineyard’s avenue, pulling up a handful and taking in its earthy scent. Asked about soil compaction, Sarah said, “There are some areas on the property with compaction, but there’s no compaction anywhere where we have applied compost.”

But this is not about large yields. It’s about creating site specific conditions in the soil, and keeping the vines just so, in order to produce the particular grape quality. “Too much moisture, and you can get fungus. Grape vines want a low nutrient condition and not too much moisture at the surface so the roots can get deep. You don’t want to coddle these plants, you have to stress them a bit in order to get the vines to produce a grape that is suitable to wine-making.”

Sarah Black explaining soil compaction

Compost benefits these vineyards by helping with water-holding capacity, reducing the potential for erosion. This is especially valuable on steep hillsides that characterize Napa Valley’s geography. Compost is part of Sarah’s best management practices.

“Compost helps build organic matter in soils, and overall healthy plants is what we are striving to maintain,” she said. “Using compost in combination with cover crops enhances soil life and this helps create an environment for healthy plants.”

Pest management is accomplished with beneficial insects. The insects are introduced by planting a mix of wild mustard, Queen Anne’s lace, and other companion plants. These plants attract beneficial insects that eat pests, including mites, mealy bugs, and aphids. The plants are placed along vine rows, avenues, field edges, and along the road edges. In 2009 the European grapevine moth (EGM) became a problem pest in the region. The winery set up EGM traps and several moths were found. In addition to an increase in the number of traps, they used pheromone dispersers in strategic locations, designed to interrupt the mating cycles of the moths and, in the process, they were able to eradicate the moth population.

Canes. Grape canes to be cut and shredded for mulch

Large blue oak trees on the property provide excellent habitat for a variety of birds that feed on insects, as well as larger birds or raptors that feed on rodents and moles. There are also bats that feed on insects.

Continuing with best management practices where nothing is discarded, the cuttings of grape canes—which are particularly woody and hard to break down—are shredded for use as mulch. The material is shredded in between the vine row and left to mulch into the soil.

Joseph Phelps Winery has been using sustainable methods in its vineyards since 1974. Their flagship wine, Insignia, was selected as wine of the year by Wine Spectator magazine in 2005 and, in part, is evidence that sustainable agriculture practices work well and contribute to the production of world-class wines.

Because of its ideal climate and growing conditions, Napa Valley has become synonymous with great wine. Sustainable practices, including annual applications of compost and using mulch to protect the soil, will be critical in the future as California copes with the impacts of global climate change, including potentially hotter summers and less rain water for growing crops of all types.

For more information contact: Compost Use in Agriculture,