Soil pH in Humboldt, CA: Lime or Sulfur?

Typical topsoil pH in Humboldt, CA

Typical topsoil in Humboldt, CA is pH 5.75, too acidic for vegetable garden. Expect roughly 9.2 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Humboldt needs, by plant

• Already in range: potatoes, strawberries, azaleas and rhododendrons.
• Lime: lawn (cool-season grass) 9.2 lb/100 sq ft over 2 applications; vegetable garden 9.2 lb/100 sq ft over 2 applications; tomatoes 9.2 lb/100 sq ft over 2 applications; roses 9.2 lb/100 sq ft over 2 applications; pink hydrangeas 5.8 lb/100 sq ft over 2 applications.
• Sulfur: blueberries 2.7 lb/100 sq ft over 2 applications; blue hydrangeas 1.7 lb/100 sq ft.

What to do next

If your test confirms pH near 5.75, spread about 92 lb of ground limestone per 1,000 sq ft of vegetable bed in 2 doses, ideally in fall.

How mixed the soil is

Of the 1,971,091 surveyed acres in Humboldt, CA, 59% are moderately acidic (5.5-6.5), 31% are strongly acidic (below 5.5), 10% are near neutral (6.5-7.3), 1% are alkaline (above 7.3). Mapped soils run from pH 3.9 to 8.3, a spread of 4.4 units across 2,147 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 21% clay and 5.97% organic matter, which this site treats as clay. At 5.97% organic matter the soil buffers like a heavier one, which pushes it into the clay bracket. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. None of the mapped components carry free carbonate.

Humboldt against the rest of California

pH 5.75 is 0.79 below the California median of 6.54. 1 of 58 California counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Del Norte (5.43), Mariposa (5.87), Amador (6), Tuolumne (6.02), El Dorado (6.04).

The range in California runs from Del Norte at 5.43 to Imperial at 8.16; Humboldt sits 12% of the way up.