How do I change the pH of my soil?

Raising the pH

To raise the pH the best practise is to apply ground limestone (calcium carbonate) or dolomite (calcium and magnesium carbonate). The recommended rate of application depends on whether the soil is sand, loam or clay. Use the table below as a guide, it is best to check instructions on limestone or dolomite packaging.

Approximate amounts of lime needed to raise the pH of top 10cm soil of different textures by one pH unit – in grams per metre squared

Soil Texture

pH 6.5 – 5.5

pH 5.5 – 4.5

Sand/Loamy sand

110 g/m2

85 g/m2

Sandy Loam

195 g/m2

130 g/m2


240 g/m2

195 g/m2

Silty Loam

320 g/m2

280 g/m2

Clay Loam

410 g/m2

320 g/m2

Organic Soil

790 g/m2

680 g/m2

Noting- if you want to convert this into tonnes per hectare; divide the number by 100.

Lowering the pH

It is economically unwise to attempt to reduce the pH of soil that is very alkaline. However, for soils that are neutral or slightly alkaline (e.g. 7.5); add 25g for sandy soil or 100g for clay soils of sulphur per square metre. This application should reduce the top 10cm of soil to between 6.0 – 6.5.