Viticulture Spring Practices - Guest Speaker

March 3, 2011 Speaker Summary


Terry Wright, Ph.D., Professor Emeritus at Sonoma State University, and a specialist in vineyard soils, spoke on terroirs of Sonoma County AVAs - the geology, the soils, and their wine “profiles” - how they relate to vigor and vineyard suitability.

We already know that “great soils and the right climate” are essential to growing quality winegrapes, and we also know that Sonoma County has the perfect combination of soils and climate and enjoys a long, slow growing season for optimally ripe fruit and small berries (Dr. Wright emphasized, more than once, that low vigor vines and small berries result in concentrated flavors.) But it was very helpful to understand, from a geologic standpoint, how these soils were created, the variety that exists, and where they are located.

The “Franciscan Complex” lies under most of Sonoma County and is 120 million years old. It consists of oceanic rocks that have been faulted and mixed; the soils here are largely sandstone and mudstone – sandy clay loam soils that have a good chemical and textural balance. The Wilson Grove Formation lies along low, rolling hills; it consists of shallow, fine-grained sea sandstone along with layers of volcanic ash (well-drained and balanced) and some fossil layers that contain high calcium. The famed Goldridge Soils in the Sebastopol/Forestville area are prime for growing Pinot noir. Sonoma Volcanic rock, which stretches further east to Napa, boasts volcanic, alluvial soils which are well- drained and balanced. Dr. Wright passed around samples of these various rocks and soils, which were very helpful to look at. One of the most interesting things Dr. Wright said was that the Russian River existed before the mountains, having established its path 3 million years ago.

The topics presented were definitely related to year-round viticultural practices and the information presented would be important to incorporate into a vineyard plan (i.e. soil mapping by experts). As Dr. Wright emphasized, the makeup of soil on any given site affects balance (the key to wine quality) – having a slow water supply (both sand and some clay); a good chemical balance (lots of calcium, less potassium and even less magnesium); and a moderate climate with an ocean influence. He also suggested the book Soils for Fine Wines as a good resource for more information.

One comment I particularly liked because it’s easy to remember: “vines are like cats – they don’t like wet feet!”