Why it matters to know the pH of your soil

The soil pH directly affects the availability of nutrients to plants. Soil pH value is a measure of soil acidity or alkalinity. The pH scale ranges from 0 to 14, with 7 neutral. Numbers less than 7 indicate acidity, while numbers greater than 7 indicate alkalinity. The scale is a logarithmic one, which means that a soil with a pH of 5.5 is ten times as acidic as a soil with a pH of 6.5, while a soil with a pH of 4.5 is 100 times as acidic as a soil with a pH of 6.5. Between 6.0 pH to 6.8 pH, the majority of plants absorb nutrients best. Nutrients for healthy plant growth are divided into three categories: primary, secondary, and micronutrients. Nitrogen (N), phosphorus (P), and potassium (K) are primary nutrients that are needed in larger quantities compared to other plant nutrients. Calcium (Ca), Magnesium (Mg), and sulfur (S) are secondary nutrients required in lesser quantities by plants for healthy growth. Zinc(Zn) and manganese (Mn) are micronutrients that are required by plants in trace amounts. Most secondary and micronutrient deficiencies can be easily corrected by keeping soil pH at optimum levels. There are different factors affecting soil pH levels, such as the parent soil type (sand, loam, clay), precipitation amounts, fertilizer applications, and the decomposition of organic matter. Soils developed from basic rock types generally have higher pH than those formed from acid rocks. While water passing through the soil leaches basic nutrients such as calcium and magnesium from the soil. They are replaced by acidic elements such as aluminum and iron. Soil in areas of higher rainfall is often more acidic than that in drier regions. The major impact that extremes in pH have on plant growth is related to the availability of nutrients to plants or the concentration in the soil of plant-toxic minerals. In highly acidic soils, aluminum and manganese can become toxic to plants. Conversely, at pH levels above 6.5, calcium, phosphorus, and most of the micronutrients become less available to plants. To make soils less acidic, the common practice is to apply material that contains some form of lime. Gardeners can choose from multiple types of ground limestone products (pulverized, granular, pelletized, and hydrated). It can take 6 to 12 months to raise the pH levels, depending on the soil type, such as clay, sand, or loam. The finer the limestone grind, the more quickly the soil pH can change. Wood ashes are also an alternative to lime, but it is not as effective. Two materials commonly used to lower soil pH are aluminum sulfate and sulfur. These products are readily available in garden sections at stores. Aluminum sulfate will change the soil pH instantly because the aluminum produces acidity as soon as it dissolves in the soil. Sulfur takes more time, and similar to lime products, the finer the grind, the faster it dissolves in the soil, lowering pH. Lime and sulfur products should be worked into the first six inches of the soil to be most effective and watered in. The most effective time to change the soil pH is before planting. Fall is the best time to make soil amendments, allowing time and nature to aid in the pH changing process. Once plants are in the ground, it is more difficult to add soil amendments without disturbing the plant roots. Several applications, taking care not to disturb roots, will be necessary and may result in only minor pH adjustments, especially for raising pH levels. The best method to determine what amendments your soil needs is to perform a soil test. The soil tests for the gardener are analogous to blood tests for a physician. The tests are an essential, inexpensive tool for the gardener. They provide detailed information on the soil composition, as well as pinpoint guidance for what amendments are required and specific application rates to address pH and nutrient deficiencies. You can purchase a soil test kit from the local OSU Erie County Extension office for $12. You can also purchase a kit directly using this link: http://agsci.psu.edu/aasl/soil-testing. Soil pH is not a static condition but changes over time. Soil tests should be done every several years. An OSU Fact Sheet on performing a soil test can be found here: https://ohioline.osu.edu/factsheet/hyg-1132