Hi Tui, I want to lower the pH in my potato bed. I understand that Aluminium Sulphate will do this quickly. Can you advise the application rate that will reduce the pH from 7 to the mid 5's?

Hi John 

Yes Aluminium Sulphate will reduce the soil pH quite quickly. The amount of Aluminium Sulphate to use is dependent on the pH change required, however adding too much of this product at the same time can cause issues with aluminium toxicity.

If you are starting with an existing garden bed we would suggest adding 100g per sqaure metre and digging this in to theb soil. This can be repeated several times over an extended period of time, with the soil pH measured to determine whether more is required to achieve the desired pH. Spread the aluminium sulphate evenly over the soil surface and dig into the top 15cm of soil. This can also be watered into the soil after digging in.

It is usually better to add this before planting into the area so it can be dug in and not cause any plant issues, but smaller amounts can be added to a planted garden bed. For existing plants we suggest adding 30g per square metre and digging this into the soil around plants, remember to water this in well. 

Thanks, Tui Team