Lawn and Garden Shop
Soil Improvement Information Series

What is soil pH?

The symbol pH is derived from Potenz = power + H (symbol for Hydrogen) and has been in use since 1909.
The term soil pH is simply a method used to express how acidic or alkaline the soil is. The standard pH range is 0 to 14 and on which a value of 7 represents neutrality and a value of 0 is extremely acid and a value of 14 extremely alkaline. The lower numbers indicate increasing acidity and higher numbers increasing alkalinity. Each change of number in either direction represents a tenfold change in acidity or alkalinity.

Most plants, whether vegetables, flowers, fruit, grasses, or shrubs require a soil pH of 6.6 to 7.0. In the Pacific Northwest, our constant rains wash minerals and plant nutrients deep into the soil or from the soil. This results in acid soils at the surface, where our plants grow..
Calicium and Magnesium are esential plant nutrients and are constantly being washed from soils and beyond the reach of plant roots.
In addition some elements in our soils are toxic to plants and this toxicity is reduced or minimized when the soil pH is between 6.6 and 7.0. This range of pH also optimizes the availability of micronutrients in the soil.

The soil pH can be changed from an acidic value toward a more aklaline value by adding Dolimite Limestone to the soil. Dolimite Limestone is a naturally occurring mineral. Powdered Dolimite lime is applied evenly over the soil surface. Then is allowed to wash into the soil or worked into the soil when possible.
The addition of Dolimite lime supplies Calicum Carbonate (CaCo3) and Magnesium Carbonate (MgCo3) to the soil. Over time these minerals break-down in the soil and provide calicum and magnesium to the soil and to our plants.
This is said to "sweeten the soil".

Dolimite limstone, in the powdered form, should be applied yearly to those soils that need to have a pH value of between 6.6 to 7.0. Spread 80 pounds per 1000 square feet evenly over the surface of the garden soil for the first year. And 40 pounds per 1000 square feet yearly after that. When possible work the limestone into the soil as soon as possible. And apply the limestone several weeks before planting because it takes time for the limestone to break down into calcium and magnesium.
Dolimite Limestone will not harm, or burn, your plants when the recommened amounts are applied. However, as a precaution keep childern and small pets away from the garden site when applying the limestone and until it is worked into the soil.

This web site was first published February 24, 2002.

This page was last updated December 04, 2015.