Gardeners have an arsenal of testing options to create the best growing environment for ornamental or edible plants. Like stabilizing a swimming pool or a fish tank, pH represents a balance between the chemical components in water, or in this instance, soil. Highly acidic water creates an orange rust in the pool or rapidly kills all the fish in your tank. Striking a balance is key to understanding any kind of pH.
Soil pH refers to the relation of acid and alkaline in a soil. Soil pH is a range of 14 numbers from zero to 14. The middle number of 7.0 pH represents a neutral solution balanced between acid and alkaline. Soil pH values lower than 7.0 indicate gradually higher levels of acid in the soil. Numbers higher than 7.0 pH refer to the alkaline side of the scale. Soil pH directly affects the availability of nutrients in the soil and the ability of plants to capture nutrients for use in growth.
Soil falling outside of the neutral range from 6.5 to 7.5 can produce distress in plants. This means that minerals, nutrients and inorganic materials aren't balanced in the soil. Acidic soils capture calcium, phosphorous, and magnesium and limit the availability of these nutrients to plant roots. The lack of balance kills off ornamental or vegetable plants. Most acidic soils occur in areas with heavy rainfall that leaches nutrients right out of the soil.
Gardeners limit acidic soils with the addition of lime to reduce acid levels. Wood ash also helps control soil acidity and shouldn't be applied at a rate over 2 pounds per 100 square feet based on recommendations from the University of Minnesota Cooperative Extension Service. Wood ash also serves as a viable source of potassium in garden soil.
Highly alkaline soils often occur in city areas or in locations with less rainfall. Gardeners often refer to the need to make soils "more acid" to reduce alkalinity. Organic products such as peat moss, compost or manure reduce alkalinity in soil. Inorganic materials include iron sulfate or aluminum sulfate.
Just as with a swimming pool, pH needs to be stable to provide the best growing environment for a plant. Each plant differs by its required pH value. Best gardening practices involves grouping plants together with similar pH needs. Changing soil pH requires patience and time to adequately change the chemical structure of garden soil. Remember to always consult with a professional to determine the best soil additives. Always mix any additives thoroughly through the planting bed to evenly distribute the amendment material.
For more information on soil pH, visit the University of Vermont Extension Service. This link includes basic soil pH descriptions, application rates, and required pH rates for common landscape plants.