Getting the “Dirt” on Yakima Valley Soils

Yakima Valley vineyards support the best Washington State and Pacific Northwest wineries  in achieving excellence. Acclaimed brands that have grown to greatness showcasing Yakima Valley grapes include Quilceda Creek, DeLille Cellars, Andrew Will, Col Solare, Côte Bonneville, Betz Family, Avennia, and many more.

What is it that makes the Yakima Valley AVA so remarkable?  One of the key elements is the soil.

We  discussed in last week’s blog how Mother Nature has blessed the Yakima Valley with a series of events that brought a variety of the most desirable soils for growing wine grapes.  Today’s blog focuses on how those soils impact the quality of the wine grapes grown in the Yakima Valley Appellation.

Sample of loess soil. Wind-deposited silt and fine sand.

Sample of loess soil. Wind-deposited silt and fine sand.

The surface layers of vineyard soils within the Yakima Valley AVA are based primarily in loess (lĕs), which consists mostly of wind-deposited silt and fine sand derived from the sediments of the ice age floods. The mineralogical content of the soils consists of a mixture of minerals derived from both the local basalt bedrock and the granites of northern Idaho and Montana.

Most of the soils in the Valley are classified as either silt loams (lohm) or fine sandy loams, which means that they have a low clay percentage relative to silt and sand. The low clay content creates well-drained soils encouraging the vines to root more deeply, a factor associated with high quality grapes and wines. It also creates an inhospitable environment for phylloxera, an aphid-like pest that feeds on the roots of grapevines.  Due in large part to the clay-poor soils, the Yakima Valley is one of the few places on earth where European wine grapes like Cabernet Sauvignon can be grown on their own roots.

Calcium carbonate on the rocks of DuBrul Vineyard

Calcium carbonate on the rocks of DuBrul Vineyard

The shallow parts of Yakima Valley soil profiles contain calcium carbonate horizons called caliche.  In most areas the caliche forms a conspicuous white layer in the soil that adds mineral complexity.

The deep roots of grapevines often penetrate through the surface layer of loess, which averages 3 ft. in thickness and into the underlying substrate. Depending on location, the substrate below the loess varies dramatically, adding diversity to the Valley’s many terroirs.

Variations in thickness of the loess, composition and texture of the underlying substrates produce a broad range of vineyard soil terroirs.

When talking to a winemaker who uses Yakima Valley fruit, he or she will note the soil differences from block to block or vineyard to vineyard. These differences are notable in the flavor profiles they produce offering that special sense of place of Yakima Valley wines.

Special thank you to Dr. Kevin Pogue, geology professor, Whitman College, Walla Walla, WA. for content contributions of today’s blog post.

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One Response to Getting the “Dirt” on Yakima Valley Soils

  1. This is an excellent discussion of loess soils and why they form the best dirt on earth in which to grow wine grapes. It pertains especially to the parts of the Yakima Valley that did not get inundated by the floods after the ice ages.

    I would like to add an addendum about the Naches Heights AVA located to the Northwest of the Yakima Valley AVA. Naches Height’s loess is called Tieton Loam and has always been above the floods. Most distinctively, Naches Height’s Tieton Loam is flavored with Andesite rather than the Basalt that influences the soils of the Yakima Valley. The Naches Heights AVA encompasses the largest flow of Andesite lava in the world, and it’s covered with 100% loess. Therefore, the Naches Heights AVA has a geologic and soil terroir that is similar, but unique, from the terroir of the Yakima Valley. Can you taste it in the wines?

    Naches Heights also has the calcium carbonate caliche layer. When you travel the area, you can see the white caliche on the Andesite rocks that were dug up when the orchards and vineyards were planted.

    Paul Beveridge
    Wilridge Winery & Vineyard

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