Soil pH - Acidity or Alkalinity

Soil acidity or alkalinity is expressed as a pH number ranging from 1.0 (extremely acid) to 14.0 (extremely alkaline). A pH of 7.0 is neutral, neither acid nor alkaline. Most plants grow best in slightly acidic to neutral soil (a pH between 6.0 and 7.0). San Diego soils that are cultivated tend to be alkaline because our irrigation water is alkaline. Soil pH affects the chemical form of some nutrients like phosphorus and iron. When the pH is too high or low, plants may suffer a nutrient deficiency even in a nutrient rich soil. When the pH is too high or low, some nutrients convert to a form that cannot be absorbed by plants. This can cause a nutrient deficiency in plants - even in nutrient rich soil.