What is aluminium sulphate or potassium aluminium sulphate?

Aluminium sulphate (Al2 (SO4)3) is a compound that is soluble in water. This compound is mainly used as a coagulant in water purification processes, wastewater treatment and in paper making processes. However, alum has a rather interesting use in horticulture.

▲Lowering soil PH — 5.0 is the appropriate pH for many garden plants that thrive in acidic environments. Aluminium sulphate helps to lower the soil pH to this target. We recommend using a soil tester to take accurate soil readings prior to use.

▲Covers all soils — Our aluminium sulphate is suitable for all types of soil, including sandy, loamy and clay soils.

▲Easy to use — If possible, mix this product into the soil and water thoroughly after application. Re-check the soil pH after at least two weeks. Reapply until the desired pH is achieved.

▲Application Chart Provided — The chart provided is approximately the amount of garden-rich aluminium sulphate needed to lower the soil pH to 5.0 (the appropriate pH for many plants).

Aluminium Sulphate Soil Amendment

Soil pH is essential when gardening. When you garden on soils with an unbalanced pH, it is difficult for plants to absorb nutrients from the soil. Alternatively, you can use alkaline soil when you want to grow acid-loving plants. Most plants grow well in slightly alkaline or slightly acidic soils with a pH range of 6.0 and 7.2.

However, some plants grow well in acidic soils. Examples of acid-loving plants include grapes, hydrangea, blueberries, rhododendron, strawberries

If you have sandy soil, the soil may be more alkaline and you will need to make it more acidic if you want to grow the above plants. 

Aluminium sulphate acidifies the soil by lowering its pH, making it suitable for acid-loving plants. When you mix aluminium sulphate with water, it forms a dilute solution of sulphuric acid and aluminium hydroxide. The sulphuric acid solution will change the acidity of the soil.

If your acid-loving plants are not thriving, you can carry out a soil test before you start adjusting the pH. If the test shows that you have alkaline soil, then you can use aluminium sulphate. 

Hydrangea plants are very sensitive to soil pH. Soil pH can change the colour of hydrangeas. If you want to turn blue hydrangea flowers to pink or blue flowers to pink, simply add alum to the soil.

Wear gloves when using the alum solution as the compound can cause irritation. If you are using the powder form, wear a respirator or dust mask to protect your lungs and throat. If aluminium sulphate chemicals come into contact with your skin, you should wash them off immediately.