The pH range required by vegetables (pH 5-7.5) just happens to coincide with the pH levels at which the nutrients in the soil are most available for uptake by plants.

As another bonus to organic gardening, plants are far more tolerant of different pH levels. In a garden where there is high levels of organic matter and a generally healthy soil, the availability of nutrients is spread over a greater pH range. Yet another reason to start with healthy, well-conditioned soil!

Below is a general guide for the pH requirements of some common crops. The Soils section contains information on how soil pH can be altered and the availability of nutrients at the different pH levels.  

pH refers to the acidity or alkalinity of the soil and is measured by the concentration of hydrogen atoms in the water within the soil. It has a direct effect on the availability of the major nutrients to the plants.

Microbial activity is also affected by the acidity or alkalinity of the soil.

Plants have a range within the pH scale where they have optimum growth.