Soil pH in Napa, CA: Lime or Sulfur?

Typical topsoil pH in Napa, CA

Typical topsoil in Napa, CA is pH 6.37, already right for vegetable garden (6-7). Test before adding anything.

What Napa needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 2.1 lb/100 sq ft over 2 applications; blueberries 3.2 lb/100 sq ft over 2 applications; azaleas and rhododendrons 2.5 lb/100 sq ft over 2 applications; blue hydrangeas 2.5 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.37, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.

How mixed the soil is

Of the 383,546 surveyed acres in Napa, CA, 48% are moderately acidic (5.5-6.5), 46% are near neutral (6.5-7.3), 4% are alkaline (above 7.3), 2% are strongly acidic (below 5.5). Mapped soils run from pH 4.6 to 7.9, a spread of 3.3 units across 111 soil components. No single class covers 60% of the county, so two gardens a few miles apart here can need opposite treatments. Test your own bed.

Clay, organic matter and rates

Topsoil here averages 22.9% clay and 3% organic matter, which this site treats as loam. Moving it one pH unit takes about 7 lb of lime or 2.3 lb of sulfur per 100 sq ft. 0% of mapped components carry free carbonate (lime already in the ground).

Napa against the rest of California

pH 6.37 is 0.17 below the California median of 6.54. 23 of 58 California counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Lake (6.28), Sacramento (6.29), Trinity (6.29), Glenn (6.34), Plumas (6.4), Santa Cruz (6.42), Santa Clara (6.44), San Diego (6.46).

The range in California runs from Del Norte at 5.43 to Imperial at 8.16; Napa sits 34% of the way up.