Why does soil pH matter to plants?

Soil pH affects how available soil nutrients are to plant roots. For example, a common problem when growing citrus on alkaline soils is iron deficiency, which presents as yellowing between the leaf veins (interveinal chlorosis).

When soils are neutral or very mildly acidic, plants can access most nutrients easily. At low (acid) or high (alkaline) pH, some nutrients cannot be utilised even if they are present in large amounts.

The natural pH of the soil tends to be acidic in moist environments where sodium, calcium, magnesium and potassium have been leached out of the topsoil.

In dry environments these salts remain in the soil, leading to an alkaline pH. For this reason blueberries and cranberries, which come from moist areas of North America, grow best in an acid soil, whereas many Australian native plants are well adapted to mildly alkaline conditions.

Soil pH can be cheaply and easily tested at home with a test kit, and amendments used to make the necessary adjustments. pH is measured on a scale from 0 (acidic) to 14 (alkaline), where a value of 7 is considered neutral.

An acid soil can be amended by applying lime, while sulphur is used to make an alkaline soil more acidic.

Follow the application rates on the product because this depends on the form of amendment being used and also on the heaviness of your soil.