Understanding pH

What is pH and how does it affect your plants?


Soil pH level is dependent on many factorsYou’ll often read the recommendation to check soil pH, but what does that really mean? pH is simply a measure of how acid or alkaline a substance is, and soil acidity or alkalinity (soil pH) is important because it influences how easily plants can take up nutrients from the soil. Many gardening books and catalogs list the preferred pH for specific plants. The good news for gardeners is that, with a few exceptions, most plants will tolerate a fairly wide range of soil pH. 

Nutrient uptake and pH: Plant roots absorb mineral nutrients such as nitrogen and iron when they are dissolved in water. If the soil solution (the mixture of water and nutrients in the soil) is too acid or alkaline, some nutrients won’t dissolve easily, so they won’t be available for uptake by roots. 
Most nutrients that plants need can dissolve easily when the pH of the soil solution 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.
Regional differences: Many environmental factors, including amount of rainfall, vegetation type, and temperature, can affect soil pH. In general, areas with heavy rainfall and forest cover such as the Eastern states and the Pacific Northwest have moderately acid soils. Soils in regions with light rainfall and prairie cover such as the Midwest tend to be near neutral. Droughty areas of the western United States tend to have alkaline soils. However, the pH of cultivated and developed soils often differs from that of native soil, because during construction of homes and other buildings, topsoil is frequently removed and may be replaced by a different type of soil. So your garden soil pH could be different from that of a friend’s garden across town. 
Changing pH: Most garden plants grow well in slightly acid to neutral soil (pH 6.0–7.0). Some common exceptions include blueberries, potatoes, azaleas, and rhododendrons, which prefer moderately acid soil. You can make small changes to soil pH by applying soil amendments. However, you’ll have best success if you select plants that are adapted to your soil pH and other soil characteristics. Adding organic matter such as compost to the soil buffers the pH, which means that it tends to bring both acid and alkaline soils closer to neutral. 
If you have your soil analyzed by a lab, the lab report will include soil pH. You can also test soil pH yourself with a home soil test kit or a portable pH meter. Home kits and portable meters vary in accuracy but can be helpful in assessing the general pH range of your soil.
The quantity of liming or acidifying material needed to change soil pH depends on many factors, including current pH, soil texture, and the type of material. A soil lab report will contain recommendations on types and quantities of amendments to use.
You can spread liming or acidifying materials with a garden spreader or by hand for small areas. If hand spreading, be sure to wear heavy gloves to protect your skin.