Tag Archives: Soil Chemistry

Soil pH [part 1]

I continue to get a lot of soil pH questions.  Growers need to realize that soil pH values, to a certain degree, are empirical.  That is, no one pH value can be declared and affirmed to be ideal or optimum for all mineral soils, and the same can be said for organic soils.  There is always room for flexibility.

A Typical Mollisol Profile

With this in mind, it is safe to say that most crops/plants are best suited to a soil pH value of 6.4 with temperate mineral Mollisols, and likewise, most plants are best suited to a soil pH value of 5.5 with temperate organic soils.  However, the older the soil, i.e., the more weathered the soil (especially pertaining to tropical soils) the lower the optimum soil pH value.

 Optimum Soil pH Values For Plant Nutrient Availability


Optimum pH

Temperate Mineral Mollisols


Temperate Mineral Alfisols






Temperate Organic Soils


For the western United States, most Arizona, California, Idaho, Nevada, Oregon, and Washington agricultural soils are Mollisols and Alfisols while most Hawaii soils are Ultisols and Oxisols.

More on soil reaction (pH) soon.  And send me your pH questions….