Soil pH in San Luis Obispo, CA: Lime or Sulfur?

Typical topsoil pH in San Luis Obispo, CA

Typical topsoil in San Luis Obispo, CA is pH 7.12, just outside the 6-7 range for vegetable garden. Test first; it may need nothing.

What San Luis Obispo needs, by plant

• Just outside, test first: lawn (cool-season grass) (off by 0.1), vegetable garden (off by 0.1), roses (off by 0.1).
• Beds or pots instead: tomatoes, potatoes, strawberries, blueberries, azaleas and rhododendrons, blue hydrangeas, pink hydrangeas.

What to do next

If your test lands near 7.12, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, roses.

How mixed the soil is

Of the 1,025,128 surveyed acres in San Luis Obispo, CA, 41% are alkaline (above 7.3), 37% are near neutral (6.5-7.3), 21% are moderately acidic (5.5-6.5), 1% are strongly acidic (below 5.5). Mapped soils run from pH 5.4 to 9, a spread of 3.6 units across 475 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 2.17% 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. 36% of mapped components carry free carbonate (lime already in the ground), enough that sulfur gets neutralised before it does much.

San Luis Obispo against the rest of California

pH 7.12 is 0.58 above the California median of 6.54. 47 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: Stanislaus (6.96), Modoc (7.04), Sutter (7.1), Orange (7.12), Riverside (7.15), Ventura (7.22), Merced (7.27), Tulare (7.27).

The range in California runs from Del Norte at 5.43 to Imperial at 8.16; San Luis Obispo sits 62% of the way up.