Another important soil factor is pH, or the measure of alkalinity or acidity. Most trees and shrubs prefer soils that are neutral to slightly acid (pH 5-7). Some exceptions to this are azaleas and rhododendrons which prefer a more acid soil (pH ~4.5). A few species, such as butterfly bush and viburnums, prefer neutral to slightly alkaline soils. Raising the soil’s pH (increasing alkalinity) can be easily done by adding lime. Making soils more acid, however, is often more difficult. Adding sulphur to the soil will temporarily lower the pH, but if the soil is too alkaline, a better practice would be to remove the existing soil to a depth of 1.5 -2 feet and replacing it with a peat-based medium.
Information about the plant’s growing needs can usually be found on the plant label or in the description of plants been offered for sale in nursery catalogs. One could also visit their local bookstore or library to consult gardening books about the specific needs of particular plants.