Tuesday, 6 November 2007

Testing the pH of Soil.

What does pH testing tell you about your soil?
Why should you bother testing your soil?

Basically a pH test will indicate whether your soil is acid or alkaline.
So? The important thing here is that some plants prefer growing in acid soil conditions and others prefer alkaline conditions.

If you are having problems and can't seem to find an adequate answer then testing the pH of your soil may be helpful.

You may have thought you had applied all the necessary goodies but if the pH is incorrect then these nutrients just won't be available to the plant roots.

Nitrogen is less available at both extremes of the scale.
Phosphorus, potassium, sulphur, calcium, magnesium and molybdenum are locked up in very acid soils.
While iron, manganese, copper and zinc are locked up in very alkaline soils.

Some of the plants growing in the garden can tell you about the pH of the soil. If known acid lovers like azaleas and camelias do well that would be an indication that your soil is a bit too acidic for more alkaline loving vegetables like cabbages and onions.

The easiest way is to test the soil.
Simple test kits can be purchased as can pH meters
but I find the kits more reliable.

Following the instructions in the kit:
  • Take a sample of soil from about 10cm (4") into the soil on the vegetable bed you wish to test
  • Use 1 teaspoonful of this soil, put it on the plastic sheet provided
  • Add the indicator liquid supplied until the soil is paste like
  • Sprinkle with the white powder provided and wait 1 minute
  • The sample has now changed colour
  • Compare the colour of your soil to the ones on the chart provided to see the pH reading of your soil.
Now you know what level your soil is at you can amend it accordingly. Most vegetables are happy within the pH range of 6 - 7.5 See the chart on this site:

It is usually recommended to add lime or dolomite to remedy acid soil and sulphur to remedy alkaline ones.

If on the other hand you're happy with the results your garden is producing then just keep making your home made compost and adding heaps of humus because this has the effect of buffering the extremes of pH imbalances.

Be aware though that increasing the humus levels in your soil may have the effect of acidifying the soil over time so occasional testing is usually recommended.

Soil Food by Jackie French
The Australian Organic Gardener's Handbook by Keith Smith


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