Soil pH in Sonoma, CA: Lime or Sulfur?

Typical topsoil pH in Sonoma, CA

Typical topsoil in Sonoma, CA is pH 6.08, already right for vegetable garden (6-7). Test before adding anything.

What Sonoma needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, strawberries, roses, pink hydrangeas.
• Just outside, test first: tomatoes (off by 0.1), potatoes (off by 0.1), azaleas and rhododendrons (off by 0.1).
• Sulfur: blueberries 2.5 lb/100 sq ft over 2 applications; blue hydrangeas 1.8 lb/100 sq ft.

What to do next

If your test lands near 6.08, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, potatoes, strawberries, roses, azaleas and rhododendrons, pink hydrangeas.

How mixed the soil is

Of the 840,376 surveyed acres in Sonoma, CA, 51% are moderately acidic (5.5-6.5), 36% are near neutral (6.5-7.3), 12% are strongly acidic (below 5.5), 1% are alkaline (above 7.3). Mapped soils run from pH 4 to 8, a spread of 4 units across 300 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 24.9% clay and 2.86% 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. 1% of mapped components carry free carbonate (lime already in the ground).

Sonoma against the rest of California

pH 6.08 is 0.46 below the California median of 6.54. 8 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: Tuolumne (6.02), El Dorado (6.04), Nevada (6.04), Mendocino (6.05), San Benito (6.09), Marin (6.11), Placer (6.13), Alpine (6.14).

The range in California runs from Del Norte at 5.43 to Imperial at 8.16; Sonoma sits 24% of the way up.