Liming Acidic Soil – Adding Lime

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Robert Pavlis

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!

Liming acidic soil
Anemone Pamina at Aspen Grove Gardens

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.

Growing Great Tomaotes, by Robert Pavlis

 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.

Liming Lawns

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?

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

35 thoughts on “Liming Acidic Soil – Adding Lime”

  1. Hi, I’m pleased with your publication on lime. I have the pH values of 6 ranging from 4.7 to 6.5. I wish to know how to get the soil pH buffer value and how to determine the lime quantity needed to raise the different soil pH to 7. Please if there is any equation for lime determination let me know.
    Thanks

    Reply
  2. I’d like to grow Pulmanaria but I have clay soil which I’ve amended with top soil and peat not realizing they prefer slightly alkaline soil. Will adding lime balance it out?

    Reply
    • No – that is a common myth. You need to get the Buffer ph value – from that you can calculate how much lime you need to add.

      Reply
  3. Hello We are battling horse hair weed It came in with one of our evergreen trees Had we known how bad it was we would have gotten on top of it but at first it looked nice. We read adding lime to the soil might help We have a huge garden bed all around the property alot to cover I am 1/3 of the way around. The root system runs up to 1 foot down and across I am digging the roots up with many offshoots. You say lime doesnt add nutrients we read somewhere that the horse hair doesnt like rich soil Have you heard of this weed any suggestions Thank yoi

    Reply
  4. My search for lime brought me here because our soil here is acidic and I read that peonies prefer alkaline soil. So, am I wasting my time if I put lime around a peony? Thank you.

    Reply
    • No idea. How acidic is your soil?

      “Peonies are very adaptable, but ideally, they like a well-drained, slightly acidic soil (6.5 to 7.0 pH). ” – so unless you have extremely low pH, you don’t need lime.

      Reply

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