A measure of soil acidity or alkalinity on a scale of 0–14, with 7 being neutral. Most vegetables prefer slightly acid to neutral soil (pH 6.0–7.0). pH affects nutrient availability — even well-fertilised soil can show deficiencies at the wrong pH.
Understanding soil pH is crucial for successful gardening across Australia's diverse climate zones. The pH scale ranges from 0 (extremely acidic) to 14 (extremely alkaline), with 7 being neutral. Most vegetables, fruits, and ornamental plants thrive in slightly acidic conditions around pH 6-7, though some plants like azaleas and blueberries prefer more acidic soil (pH 4.5-5.5), whilst lavender and clematis prefer alkaline conditions (pH 7-8).
Australian soils vary significantly by region. Coastal areas and tropical zones often have naturally acidic soils, whilst inland and semi-arid regions tend toward alkaline conditions. You can test your soil's pH using inexpensive test kits available at Bunnings or by sending samples to your state's agricultural department. If your soil is too acidic, add lime (calcium carbonate) to raise pH. If too alkaline, incorporate sulphur or acidifying fertilisers to lower it.
Soil pH affects nutrient availability dramatically. In acidic soils, nutrients like magnesium and calcium may wash away, whilst in alkaline soils, iron and manganese become locked up and unavailable to plants. Seasonal variations matter too; autumn and winter are ideal times to amend pH as soil microbes work slowly. Always allow 2-3 weeks after pH adjustment before planting, as changes take time to stabilise throughout your garden bed.