Soil pH: What It Tells You—And What It Doesn’t


Soil pH is a hot topic among gardeners and one worth taking a look at. People talk about how ‘acidic’ or how ‘alkanine’ their soil is but they don’t always consider other factors that are essential to proper soil management.

Let’s start with a basic pH primer.

Like the temperature of the human body, pH is an important measurement of soil health. It affects the number and activity of beneficial soil microorganisms, and impacts the availability of essential nutrients.

The pH scale goes from 0 to 14 with 7 considered as ‘neutral.’ Basically, pH measures the amount of hydrogen in the soil compared to other nutrients such as magnesium, calcium, potassium, sodium and aluminum. pH is an inverse function, which means:

  • More hydrogen (and less of other nutrients) = a lower pH number (i.e., the more ‘acidic’ the soil)
  • Less hydrogen (and more of other nutrients) = a higher pH number (i.e., the more ‘alkaline’ the soil)

Soil pH typically ranges from 4 to 9, but widely accepted garden wisdom says that anything between 6 and 7 is best for growing strong and healthy plants. Although this is generally true, pH balance is just part of the equation. Proper soil management requires a bit more investigative work on the gardener’s part.

For example, many well-meaning gardeners apply dolomite lime to their soil every year to reduce acidity and raise pH levels. In doing so, they are also adding calcium and magnesium which is present in lime. Do plants need these nutrients? In what ratios? The pH value on its own does not provide any insight.

Let’s say you are trying to grow rhododendrons, azaleas or blueberries—all considered ‘acid-loving’ plants. Garden sites advise adding sphagnum peat or chemical fertilizers to make the soil more acidic. But what if your plants are missing essential nutrients or trace minerals? Again, the pH value on its own doesn’t provide enough information.

A better bet is a comprehensive soil test. By sending a soil sample to a lab, you not only get a pH value but also a detailed analysis of soil nutrients (and deficiencies). For ongoing soil management, use a high quality compost mixed with all-natural rock dust like Cascade Minerals Remineralizing Soil Booster to give plants the essential minerals and trace elements that they need while buffering both high and low pH levels.

To assess your soil for even more qualities, use a DIY system called the “Willamette Valley Soil Quality Guide” which was developed by a team of farmers and soil scientists in Oregon. The methods are simple and the only supplies you need are common household items. More details at Organic Gardening.