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Soil pH is a figure which indicates how acid or alkaline your soil is. The abbreviation "pH" stands for potential of Hydrogen. A soil which is neutral (i.e. neither acid nor alkaline) has a pH value of 7. A pH value of lower than 7 indicates the soil is acidic (the lower the value the more acidic the soil); a pH value above 7 indicates the soil is alkaline (the higher the value the more alkaline the soil).
Some plants grow better in a moderately acidic soil and some plants grow best in a moderately alkaline soil. Just as importantly, some pests and diseases are more active in acid or alkaline soils.
For example, azaleas and camellias grow best in a moderately acidic soil whereas geraniums and garlic will grow well in alkaline soils. As far as pests and diseases go, potatoes are more like to suffer from scab in an alkaline soil whereas clubroot of susceptible vegetables will thrive best in an acid soil.
For most plants and vegetables a soil pH around 6.5 is the ideal although anything in the range 6.2 to 6.8 is fine. Lime hating plants such as azaleas and camellias are the exception, the definitely do prefer an acidic soil with a pH value in the range 5.2 to 5.9.
There are several soil pH testing kits available both online and from garden centres. An example of one is shown in the picture below.
Soil pH Testing Kit
These work well and they are easy to use. They contain enough kit for 100 tests and provide results in a matter of minutes. There are alternate testing kits which consist of one or two prongs which are simply inserted into the soil to give a reading, these also work well.
It is easy to become a bit obsessed with soil pH but once tested, soil only changes its pH very slowly and testing every two or three years will be sufficient.
Do not perform a pH soil test within three months of adding lime, any chemicals or large amounts of organic matter - all those will cause the tests to provide inaccurate results.
If you want to make the soil more alkaline (i.e. increase the pH), the easiest method is to add lime which readily available at garden centres and through online suppliers.
If you want increase the acidity of the soil (i.e. decrease the pH), the cheapest and safest method is to use sulphur chips. Allow a couple of months after application for it to take effect.
Read the instructions on the pack carefully before applying lime or sulphur, if too much is added it can take a long time to correct the situation.
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