It is easy to measure and is usually listed numerically on a scale of one to 14. Acid soils have a pH of below seven, neutral is pH 7 and alkaline is above seven. For most garden plants a neutral soil is ideal but some, such as rhododendrons and camellias, must have an acid soil. Others, including many clematis and lilacs, prefer alkaline conditions. The majority of amateur soil testing kits are very simple and rely on colour rather than a numerical scale.
Acid soils turn a solution yellow-orange, neutral turn it green and alkaline, dark green .