Understanding Soil pH

Look in any gardening book, under the section that deals with descriptions of how to grow individual cultivars, and they will invariably have some reference to the soil pH for that particular plant.

Infact, soil pH, for the most part, is just slotted in to a description, almost like an after thought, usually between the:- likes a sunny position and how tall the plant grows.

For something SO important and vital for the survival of the plant, I am amazed the subject is often overlooked, or just a brief passing comment is made.

Why is soil pH important?

Because, the correct soil pH is a plant’s metaphorical life’s blood. It is the gate keeper, with the keys to unlock the soils potential for releasing minerals and trace elements that are imperative to the health of any plant.

The pH of the soil determines which nutrients are made available to the plants at any given time. For example:
In a soil with a pH6 or lower and soils with pH8 and higher, the plants will not have access to phosphorus, which is important for cell division especially in new seedlings.

In a soil with a pH5.5 or lower and soils with pH 8.5 and higher, the plants will not have access to nitrogen, an essential element for new growth and an essential part of chlorophyll.

(See: What Do Minerals and Trace Elements Do? for detailed information on all minerals and trace elements )

What does pH mean?

To begin to understand soil pH, it is helpful to look at the definition of what pH is. The Oxford English dictionary defines pH as:
Noun, chemistry.
A figure expressing the acidity or alkalinity of a solution on a logarithmic scale in which 7 is neutral and lower values are more acid and higher values are more alkaline.

What it basically means, is, pH is a measurement of the acidity or the alkalinity of a substance, to measure soil pH you have to mix some soil into water and then add a part of this ‘substance’ to a pH measurement kit, and the result will be a colour coded number which correlates to a number on the pH scale.

The pH scale is a fixed scale on which 7 is the middle ground, neutral, anything higher than 7 is more alkaline and anything below 7 is more acid.

The pH scale began in the early 20th century coming from the ? representing the German word ‘potenz’ which means power and includes H, the symbol for hydrogen.

Why understand your soil pH?

Understanding soil pH will benefit you and your plants, because all the nutrients they require are only available in a very narrow pH range, 6.5 to 7.5. Infact, few plants will survive in a soil pH of 4 and a soil pH higher than 7.

The majority of plants thrive in a soil with a pH 6 to 7 and most vegetables will thrive in a soil with a of pH 6.5.

And, nature does it’s own work, for example: acid loving plants have actually evolved over time to require less of the major elements and more or the trace minerals, like iron, and thrive in a soil pH 5 to 6.

As a general rule, it is said, rainy climates have a higher potential for an acidic soil and dry/arid climates have a potential for being neutral/alkaline. (I have not found any information to why this may be, but, as soon as I do I will pass it on.)

Fact:

The Earth, has provided all the soil, any where in the World, with enough minerals and trace elements to last thousands of years. But the pH of the soil prevents these nutrients from being released even though they are there.

Here in New Zealand, we are told our soil is deficient in Boron and Selenium, but, infact, these elements are in the soil, but are not available because the soil pH is incorrect – to much lime and super phosphate sprayed over and over again, year after year, without any real necessity.

How Do I Find Out What My Soil pH Is?

There are many commercial soil pH testing kits available, prices vary with the sophistication of the individual kits. Which ever you choose, the actual testing is a relatively simple procedure.

The cheaper end of the price range will only tell you what the pH range is, while the more expensive kits, will not only tell you your pH range, but also tell you what elements and nutrients your soil is lacking.

Now, there is a draw back, your garden area can contain many different soil mixes, so, you will need to test every different patch to get an accurate overall view of your soil pH.

But, you know me, save the pennies and the $ look after themselves!! So, I have a few ways you can test your soil pH and save money, bear in mind though the following ways will give you a ‘rough’ idea of what your soil’s pH is and they will not give you a detailed information on which elements and nutrients you are missing.

Home-Made Testing Kits

The Taste Test: Oh yes, some gardeners will taste their soil to get an indication of it’s pH, mainly used for testing for acidity. Acidic soil will smell and taste sour.

The Vinegar Test: If the above, is not for you, try dropping a little soil into a jar filled with vinegar. If the mix bubbles, you have a reasonable neutral pH, if there are no bubbles, you need to do a bit of work to correct the pH.

The Red Cabbage Test: This is my personal favorite!! You will need to:
1) Boil 500g of red cabbage in 1L of water, until the water is quite purple.

2) Drain, and retain the water. In a separate container, mix 2 Table spoons of soil with 1 cup of distilled water (Get this from a pharmacy) leave this mixture over night.

3) Fill a jar to 3/4 full with the cabbage water, then, carefully, remove approximately 50mls of the distilled water mix, add this to the jar with the cabbage water.

4) Let it mix together and leave it for a few minutes, then compare the colour in the jar with the chart below:
Color pH
Magenta 3
Violet 5
Blue 7
Blue/Green 9

What can I do if my soil pH is wrong?

Firstly, if your plants are showing any signs of a nutrient deficiency, it is imperative to test your soil pH first, to establish what it is, as it could be the pH of the soil that is holding back the vital nutrient.

Important, because if symptoms of nutrient deficiency are treated before adjusting the pH of your soil, a condition known as ‘nutrient toxicity’ can occur, this is when plants are over whelmed by the sudden overload of nutrients that are swamping their systems.

Also, it is easier to improve your soil pH by adding moderate amounts of compost, organic matter and organic fertilisers. And continued use of these will restore your soil to a very healthy soil, naturally.

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