Tuesday, August 14, 2012

The difference between Garden Lime and Dolomite Lime

I've always called it the ‘soil sweetener’.

I’m not kidding, it really has produced some of the best crops in my garden. I get tremendous feedback about how tasty my roots vegetables always turn out. I will give a lot of the credit to Gardening Australia teaching me about always applying a handful of Lime to every garden bed.

A lot of other keen to learn gardeners have asked me to explain what all the different Limes do, so that's my topic today.

So what is Lime?

Garden Lime and Dolomite Lime are both used to correct soil acidity, making it more alkaline.

They both come in the form of (crushed rock) white powder; the finer the lime is the better it is for the soil to absorb.

A favourite pH stabilizer for most gardens has always been Dolomite Lime. Dolomite has a neutral pH of 7 and will never go above pH 7.

  • Dolomite Lime contains both calcium (Ca) and magnesium (Mg).
  • Garden Lime or Agricultural Lime contains more calcium (Ca).

Garden Lime is faster acting than Dolomite Lime and therefore costs a little more.

One thing Lime does not prevent is toxic salt build-up caused by fertiliser build-up or impure water.

Builders Lime is NOT the same as Dolomite or Garden Lime and is therefore not safe for the garden. Builders lime is hydrated lime, made from limestone, from 'burnt lime' which is heated to make it more concentrated and then hydrated with water, very reactive and likely to cause root burn if you are not careful. Dolomite and Garden Lime are safe to the touch.

Why do we need to use Lime?

Most soils that are regularly fertilised will become more acid over time and this may affect plant growth. The acidity of the soil controls the availability of valuable nutrients to the growing crops.

If the soil is the wrong pH for the plant it will not be able to absorb all the nutrients to promote growth, no matter how much fertiliser is applied. Acid soils reduce plant growth by inhibiting the intake of major plant nutrients (nitrogen, phosphorus and potassium).

Acid soils (low pH) have less calcium whereas high pH soils normally have more.

What affects the soil pH to change?

Rainfall affects soil pH. As water runs through the soil leaches basic elements such as calcium (Ca), magnesium (Mg) and potassium (K). These are generally replaced by acid elements of aluminium (Al) and hydrogen (H).

Crop removal can also contribute to the change in soil pH. That is why Lime is added prior to new crops being sown.

Different soil types react differently to soil pH levels.
For example, clay soils are harder to work the more acid they are.
Clay soils usually become acid quicker than sandy soils and the amount of organic matter has an effect. Clay soils may also react slower to the addition of lime.

pH meter

How do I know if my soil needs Lime?

One of two ways
  • Soil Test Kit
  • pH Meter

When should I add Lime to my garden bed?

The best time is when you are digging over your garden bed (around 1 month prior to planting). Sprinkling handfuls liberally over the bed and digging through is all that is needed. Combining this with handfuls of Blood and Bone and well-rotted manure is a great way to replenish any garden bed.

Handful per square metre is ideal.

My only warning is not to add Lime when you have produce already in the ground as it may damage the harvest. It’s really hard to ever over use Lime, otherwise. Your garden will thank you for it.

Lime is definitely going to be your new best friend in the garden♥

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