There are so many variables in wine and plenty just within the vineyard.

A Vineyards “Terroir” or sense of place come from the weather, the location of the vines on slopes for more or less sun, coastal influences, temperature fluxuations, cover crops, and soil.

After our recent trip to Paso Robles I was curious about the calcareous soil and the differences between the soil types for east side and west side vineyards.  So we will explore that here today.  The subject is complex and I will only deal with some of the basics, but I will happily provide links for further information.

Paso Robles sits south of San Francisco and North of LA.  Well, that’s pretty basic isn’t it?  This area is considered California’s Central Coast.  Paso’s west side begins just 6 miles from the Pacific Ocean.  The Santa Lucia Mountains give us the western border.  The AVA is about 35 miles east to west and 25 north to south.  That encompasses 614,000 acres of land about 26,000 of that planted in vineyards.

There are over 45 different soil types found in this area and they tend to be mixed!  You can find vineyard blocks whose soils vary row to row.

Tablas Creek Soil

So what makes the really good stuff?  Well these days in Paso especially on the west side you will hear quite a bit about the Calcareous soils.  This soil is limestone based and comes from this land at one time being an ocean floor.  Whale bone Winery is named for the actual whale bones that they unearthed when they were planting their vineyard.  All of this ancient sea bed was pushed up with the mountain ranges by the geological plates.

On Paso’s westside you find huge chunks of limestone.  As the limestone gets wet it becomes softer and chalkier and the roots of the vines can then push through and did deep to get to water.  The limestone rock also holds heat from the 100 degree days keeping the vines warm at night when the temperatures drop to 45 degrees.  This soil type is similar to that of Chateau-neuf de Pape which is what brought the Perrin Family here with the Haas family to grow Rhone varietals here in California at their Tablas Creek Winery.  These Calcareous soils also have soil pH of 7.4 to 8.6 and this is not found in other areas of California.  This higher pH is helpful in that it increases the availability of phosphorus and nitrogen. Calcium based soils retain water well but do not become water logged during heavy rains.  High pH in calcium rich soils has been shown to help maintain acidity late in the growing season.  So you can increase the hang time to get riper fruit without sacrificing acid!

On the east side of Paso you find loamier soils due to the Salinas River that runs between the east and west side.  With fewer hills this soil tends to be more fertile and easier to cultivate as the hills roll rather than having steep hills.  With less limestone in the soils the pH is lower and as such more hang time can compromise the acidity of a wine.

Okay, so I sound like a commercial for Calcareous soil.  Now let me tell you a little about the east side soils.

There is still calcareous soil on the east side, but it is mixed with clay and sandy loam.  Gravely and clay loam make for great drainage and cause low vine vigor which intensifies the flavor in the berries. Nacimiento – Los Osos complex  soil is found often on the east side.  These complex soils are well drained but are relatively poor and have chalky or gravelly components.  Due to the heat on this side you find more of the big bold varieties grown here such as: Cabernet Sauvignon, Syrah, Merlot, and Petite Sirah.

So is one soil type better than another?  It depends on the grape, the vineyard climate and sun, and the winemaker.  Soil is another one of the many components in creating wine.

For more information on the soils of Paso Robles look for the book Paso Robles: An American Terroir or just about anything written by Dr. Thomas Rice who teaches at Cal Poly.  Some of his work can be found here http://works.bepress.com/trice/