Soil pH Simplified
Soil acidity or alkalinity affects plant growth by influencing the chemical availability of the nutrients in soil for uptake by plants. Acidity or alkalinity of soil is determined by its lime content. Soil pH test kits are easy to find at your local hardware store. PH is measured on a scale of 1 to 14. neutral soil has a pH of 7; anything above that is alkaline, and anything that is acid.
Fortunately, most plants will tolerate a fairly wide range of soil pH. Most nutrients that plants need are readily available when the pH of the soil solution (mixture of water and soil nutrients) ranges from 6.0 to 7.5. Below pH 6.0, some nutrients such as nitrogen, phosphorus and potassium, are less available. When pH exceeds 7.5, iron manganese and phosphorus are less available. Adding organic matter to the soil, regardless if it is acid or alkaline, tends to make the soil more neutral.
Blueberries and potatoes prefer moderately acid soil. It is easier to make an acid soil more alkaline by adding lime than the other way around. Adding lime to heavy clay soils will help bind the particles together. However, too much lime can chemically “lock up” some of the plant nutrients, particularly trace elements, so that they are unavailable to the plant roots, resulting in nutrient deficiencies.
In general, droughty areas of the western U.S. tend to have alkaline soils. By selecting plants that are adapted to your soil pH and other soil characteristics, you will have the best success. Otherwise, alkaline soil may be corrected by adding a source of acidity. The most common material to add is elemental sulfur. However, there is no simple rule on how much sulfur to add. Mixing peat moss with the soil will also lower pH.
- Written by Mary Hartford Mary Hartford
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