Soil pH in Contra Costa, CA: Lime or Sulfur?

Typical topsoil pH in Contra Costa, CA

Typical topsoil in Contra Costa, CA is pH 6.69, already right for vegetable garden (6-7). Test before adding anything.

What Contra Costa needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, roses.
• Just outside, test first: strawberries (off by 0.2), pink hydrangeas (off by 0.2).
• Sulfur: potatoes 4.1 lb/100 sq ft over 3 applications; blueberries 5.8 lb/100 sq ft over 3 applications; azaleas and rhododendrons 4.8 lb/100 sq ft over 3 applications; blue hydrangeas 4.8 lb/100 sq ft over 3 applications.

What to do next

If your test lands near 6.69, 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 375,098 surveyed acres in Contra Costa, CA, 49% are near neutral (6.5-7.3), 39% are moderately acidic (5.5-6.5), 12% are alkaline (above 7.3). Mapped soils run from pH 5.5 to 8.2, a spread of 2.7 units across 144 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 35.2% clay and 2.49% organic matter, which this site treats as clay. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. 21% of mapped components carry free carbonate (lime already in the ground).

Contra Costa against the rest of California

pH 6.69 is 0.15 above the California median of 6.54. 31 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: San Diego (6.46), San Francisco (6.5), Madera (6.58), Solano (6.63), Santa Barbara (6.69), Sierra (6.71), Los Angeles (6.72), Fresno (6.75).

The range in California runs from Del Norte at 5.43 to Imperial at 8.16; Contra Costa sits 46% of the way up.