Soil pH is a measure of the acidity or alkalinity of soil. It's measured on a scale of one to 14, with seven as the neutral mark. So, anything that measures below seven is considered acidic and anything above seven is considered alkaline. Gardeners should know whether their soil is alkaline or acidic because some plants require nutrients that can only be retrieved when the soil pH level falls into an certain range. Hydrangea, for example, will blossom in either pink (alkaline) or blue (acidic), depending on the soil pH. For Good to Grow month, this is a good term to know!