Soil pH in Marin, CA: Lime or Sulfur?

Typical topsoil pH in Marin, CA

Typical topsoil in Marin, CA is pH 6.11, already right for vegetable garden (6-7). Test before adding anything.

What Marin 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 2.1 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.11, 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 0 surveyed acres in Marin, CA, 68% are moderately acidic (5.5-6.5), 23% are near neutral (6.5-7.3), 8% are strongly acidic (below 5.5), 2% are alkaline (above 7.3). Mapped soils run from pH 4.5 to 8, a spread of 3.5 units across 169 soil components. 68% of the land falls in one class, so the county figure is a fair first guess for most yards here.

Clay, organic matter and rates

Topsoil here averages 24.3% clay and 2.68% 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).

Marin against the rest of California

pH 6.11 is 0.43 below the California median of 6.54. 10 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: Nevada (6.04), Mendocino (6.05), Sonoma (6.08), San Benito (6.09), Placer (6.13), Alpine (6.14), Calaveras (6.17), Shasta (6.17).

The range in California runs from Del Norte at 5.43 to Imperial at 8.16; Marin sits 25% of the way up.