However, soil scientists have found that plants generally need a small amount of acidity in the soil to grow well. The ideal soil pH for many ornamental plants is within the range of pH 5.5 to 6.5, where most nutrients are available. In very acidic soil, some elements change from beneficial to harmful. Below pH 4.0, aluminum and manganese become toxic to plant roots. In highly alkaline soil, manganese and boron are relatively unavailable.
Some plants have specific pH preferences.
Since they have evolved for millennia in a moist, acidic environment, their roots have adapted. Acid-tolerating plants function best at about pH 5.2, but tolerate conditions a full pH point above or below that level. Conversely, many grasses and grains evolved in a low-rainfall, slightly alkaline environment. You can have it measured by a university laboratory through your local cooperative-extension service or a commercial agricultural laboratory. You can also purchase soil-testing kits from garden stores or catalogs.