Your soil is acidic and you would like to change the pH so that it is less acidic. The universal advice is to add lime to the soil ie liming your soil. Lime is alkaline and it will neutralize the acidity of the soil and make it more neutral. Adding lime certainly works – but there is a catch!
What is Lime?
Strictly speaking lime is calcium oxide or calcium hydroxide, but the term is also used to describe a wide range of calcium-containing compounds. Agricultural lime is usually calcium carbonate, or limestone. All of these soil conditioners will neutralize acids and make them less acidic.
Liming – What Happens in the Soil?
Soil is able to ‘buffer’ itself. What this means is that you can add a bit of lime to acidic soil, and the pH of the soil does not change. This ability of the soil to neutralize the lime is called ‘buffering’. If you keep adding more and more lime, you will reach a point where the soil just can’t buffer any more, and the pH will start to go up. How much does your soil buffer? That is an important question when adding lime because you need to add enough lime to overcome the buffering effect and then add more to change the pH.
The buffering effect of soil can be measured and it is called the “Buffer pH”. Without knowing the Buffer pH, you simply do not know how much lime to add to your soil.
How do You Measure Buffer pH?
A commercial soil testing lab can measure and report the “Buffer pH”. Using this value it can then recommend the amount of lime you need to add to the soil.
In a previous post I discussed the accuracy of soil testers in Soil pH Testers – Are They Accurate?, but an even bigger problem with these testers is that they don’t measure Buffer pH.
Since garden soil kits don’t measure the Buffer pH, they aren’t much use for adjusting the pH of acidic soils.
A lot of gardening information recommends that you should add lime to your lawn on a regular basis. As you can see from the above discussion you can’t know how much to add without a soil test. Don’t add lime to your lawn unless a soil test tells you that it is required.
If you are trying to get rid of moss in your lawn because of the acidity have a look at this post; Why Does Moss Grow in My Lawn?