The biggest and best improvement you can make to your soil is knowing your soil’s pH and changing it where necessary.

What is pH?

The pH of the soil is a measure of the acidity or alkalinity of the soil.

pH actually means “potential hydrogen” and is a measure of hydrogen ion concentration.

Because hydrogen ion concentration varies over a wide range, a logarithmic scale (pH) is used.

The scale runs from 0 to 14, with 7 being neutral. Soils lower than 7 are acidic and those higher than 7 are alkaline.

As the scale is logarithmic, this means that a pH 6 is 10 times more acidic than pH 7 and pH 5 is 100 times more acidic than pH 7!

Why it’s Important to Test Your Soil’s pH?

Plants that are well nourished and healthy are less likely to be attacked by pests or diseases.

Your soil’s pH affects the availability of the nutrients in your soil.

Some nutrients are more available under acid conditions, while others are more available under alkaline conditions (see graphic below)!

Nitrogen, phosphorus, potassium and sulphur are readily available between pH 6 to pH 7, but are less available when the pH is less than pH 6 or higher than pH 7.5.

When your plants are showing signs of nutrient deficiency, before you give the plant trace elements, check the pH of the soil.

There may be plenty of nutrients in the soil, but they may not be biologically available to your plant because the pH is wrong.

Alternatively, the wrong pH can attract the wrong plants, such as Nutgrass which loves an acidic soil that’s low in calcium!

How to test your soil’s pH using a pH test kit

Soil pH test kits are available from nurseries and hardware stores and the instructions are really easy to follow. I have outlined the main steps below:

• Take a small sample of your soil, around a teaspoon is ideal.
• Make sure you dig down to the depth of the main roots around 10 cm or even deeper for trees, as the pH on the surface won’t be an accurate reflection of what your plant is experiencing;
• Place the soil sample on the plastic tile in the test kit;
• Add a few drops of indicator dye from the kit to the soil sample and stir using the applicator;
• Puff on the barium dust (white powder) from the kit;Alkaline soil
• Wait for 30 seconds for the colour of the white powder to change;
• Match the colour of your soil sample with the colour the chart.

      
Highly acidic soil sample                                          Highly alkaline soil sample

Take a lot of samples from different parts of your garden as the pH can change over distances depending on how you have treated your soil.

Fertilisers, especially non-organic ones, composts, manures and various other gardening practices can impact on the pH of your soil.

It is a good idea to check your soil annually so that you can adjust the pH for the needs of your plants.

Changing your soil’s pH

If your soil is too acidic, and you need to raise the pH, you can add any of the following:

• compost
• poultry manure
• wood ash
• agricultural lime or dolomite

Mature compost usually has a pH 6.5 and can be added to both alkaline and acidic soils.

However, it is always best to check the pH of your compost, as it may be higher than expected. This is likely if you have added chicken manure or wood ash to your compost as these products are more alkaline.

If your soil is too alkaline you want to lower the pH you can add any of the following:

• compost
• animal manures, especially horse, cow or sheep (not poultry)
• leaf litter or mulch
• sulphur either powder or liquid

Always remember to alter the pH slowly as you don’t want to go from one extreme to the other.

So, What’s a Good pH level?

For the vegetable gardener, a pH of 6 to 7 is ideal for most plants.

Other herbs and vegetables, especially those from Mediterranean climates such as rosemary, brassica, sage and asparagus prefer a more alkaline soil.

Some fruits including citrus, blueberries and strawberries prefer a more acidic soil.

That’s why I give my blueberries a drink of black coffee every week!

Happy gardening from Rohanne, your Edible Garden Guru

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