pH stands for 'potential hydrogen'. It refers to the ability of a plant to attract hydrogen ions.
The pH scale is a reference grid which shows how acidic or alkaline a solution is.
The pH scale runs from 0-14, with 0 being a maximum concentration of acid and 14 being the maximum concentration of alkaline.
At pH 7, there is a balance between acid and alkaline solutions.
A universal indicator is a mixture of dyes which change colour gradually over a range of pH's. Any substance with more than one colour form can be used as an indicator.