Importance of Soil pH

Soil pH is a measure of the soil's acidity or alkalinity measured on a scale of 0 to 14, with 7 being considered neutral (neither acidic nor alkaline). Moving down the scale closer to 0 (zero), the pH is considered more acidic. Moving up the scale closer to 14, the pH is considered more alkaline. In simple terms, the closer to zero you go, the closer to battery acid you get and the closer to 14 you go the closer to drain cleaner you get.

As a basic reference the following chart is a good example of common items and their lcoation on the pH scale:

There are more graphic examples out there - but you get the idea.

So why is this important for your plants? Soil pH directly affects nutrient availability and the toxicity of minerals to your plants. Aluminum and manganese become more available in acidic soils, while calcium, phosphorous, and magnesium are less available. In alkaline soils, phosphorous and most micro-nutrients become less available. Depending on what nutrients your plants require and in what quantities will determine the optimal soil pH level.

Most plants prefer a relatively neutral soil pH (between 6.0 and 7.5, approximately). Some plants do thrive in acidic conditions (pH of 4.5 to 6.5) and some in alkaline conditions (pH of 7.5 to 8.0). The Old Farmer's Almanac has a good listing of plants and their preferred pH ranges.