Napa County Soil Data
Napa County, California
Avg pH
6.2
Texture
Silty clay loam
Drainage
Very poorly drained
Organic Matter
5.3%
Hydrologic Group
C/D
Data Story
About Soil in Napa County, California
The Acidic Foundation of Napa Valley
Napa's dominant Entisols show a pH of 6.15, which is notably more acidic than the national median of 6.5. These young, mineral-rich soils provide the specific chemistry that fuels the county's world-class vineyards. This acidic profile is a key component of the region's unique terroir.
Balanced Texture for Silty Clay Loam
The county's silty clay loam consists of 34.7% sand, 37.5% silt, and 24.7% clay. This balanced distribution offers excellent structure and moisture retention for deep-rooted crops. It provides a stable environment that is easy to work while still providing enough body for plant support.
Exceptional Organic Matter Levels
Napa boasts an organic matter content of 5.28%, far exceeding the California state average of 3.30%. The available water capacity of 0.140 in/in stays competitive with the state average of 0.141 in/in. These high carbon levels translate to superior nutrient availability and soil health.
Navigating Poorly Drained Lands
The soil is classified as very poorly drained and falls into hydrologic group C/D. This indicates slow water movement and high runoff potential, especially during heavy winter rains. Proper drainage infrastructure is vital for protecting both agricultural yields and residential foundations.
Premier Growing in Zone 9b
Hardiness zone 9b combined with rich soil makes Napa a haven for wine grapes, olives, and citrus. The high organic matter provides a natural head start for any home vegetable garden or professional vineyard. Dig in today to take advantage of some of the most fertile ground in the state.
Soil Composition
Soil pH
Soil Series
Detailed soil series data not yet available for this county.
Hydrologic Group
Group C — Moderate-High Runoff
Soils with slow infiltration rates, often with a layer that impedes downward water movement. Higher clay content restricts drainage.
Drainage Class
Very poorly drained
Water is removed so slowly that free water remains at or on the surface most of the year. Typically wetland soils.
Soil Profile
Dominant texture: Silty clay loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Frequently Asked Questions
What type of soil does Napa County have?
Napa County's soil is classified as Silty clay loam. This indicates the relative proportions of sand, silt, and clay — 35% sand, 38% silt, and 25% clay. Loamy soils hold moisture well and support a wide range of plants.
Is Napa County's soil acidic or alkaline?
Napa County's soil has a pH of 6.2, which is moderately acidic. This range suits many crops and is common across much of the eastern US.
What is the drainage class for Napa County?
Napa County has a dominant drainage class of "Very poorly drained." Poorly drained soils retain water for extended periods, which can limit crop choices and may require tile drainage or raised beds.
What crops or plants grow well in Napa County's soil?
Based on Napa County's Silty clay loam texture, pH of 6.2, and Very poorly drained, the soil is well suited for vegetables, grains, and most field crops, row crops and vegetable gardens, rice, cranberries, and other water-tolerant species.
What USDA soil order is found in Napa County?
Napa County's dominant soil order is Entisols. Entisols are recently formed soils with little to no horizon development. They are common on floodplains, steep slopes, and sandy deposits.
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Other Counties in California
Soil data sourced from USDA SSURGO via Soil Data Access. Data is informational only and should not be used as a substitute for on-site soil testing. Contact your local NRCS office for site-specific soil information.