Soil is the foundation of the garden. It anchors the plant’s root system, holds nutrients and water to nurture the plant, and provides a home for micro-organisms. Healthy balanced soil means healthy plants. One of the indicators of healthy soil is the pH. So, what is pH and why does it matter?

Put very simply, pH stands for ‘potential of hydrogen’ and determines the availability of almost all essential plant nutrients. It can affect a plant’s ability to absorb vital nutrients from the soil. It is measured on a scale from 0 to 14. The lower the number, the more acidic the soil and the higher the pH the more alkaline it is.

The middle of the scale, 6.5 to 7.5, is considered neutral and most plants thrive in neutral soil.

However, some plants prefer growing in sweet, alkaline soil and some need more sour acidic soil to thrive. It is important to understand the needs of your plants so that you can create the best soil conditions for them to thrive.

It’s best to check the soil pH and fix any issues at the source. Simple testing kits are available so that you can do the test at home, or bring in a sample of your soil to the Garden Centre and we will do the test for you.

The soil in Perth tends to be alkaline (above 7) and may need to be adjusted to make it more neutral. When the pH rises above neutral, key nutrients needed for healthy plants such as  iron, manganese, copper, boron and zinc can be locked up in the soil.

Plants not adapted to these pH conditions suffer nutrient deficiencies, often shown by yellowing in the leaves, or dark green veins against a pale green leaf.

There are many ways to decrease the alkalinity of soil. Compost is a great way to improve the structure and feeds soil microbes. When it breaks down it releases humic acid into the soil and helps adjust the pH.

While iron maybe available in the soil, the high pH slows the uptake by the plant. A quick solution is to apply iron chelates. The powder is watered onto the roots and new leaves appear green in about a week. However, the effect is short term and it is better to invest time and energy in adjusting the pH long term.

If the soil test shows a result above neutral, select plants that have adapted to more alkaline conditions. Many Mediterranean plants and Australian natives grow well in these soils.

If your soil pH is below 6.6 (so it is acidic) you need to add lime to shift it towards neutral. Or you can select acid loving plants adapted to these pH conditions. Azaleas, camellias, rhododendrons, gardenias, blue hydrangeas and blueberries are common plants that need acidic soil.

If you want to grow acid loving plants in alkaline soil and need to adjust the soil pH to 5-6.5, add GreenLife Soil Co. Acid Concentrate. This mix has loads of nutrients, organic matter and minerals (including Charlie Charcoal) to help hold water.

Searles Sulphur Powder is also an excellent acidifying agent for lowering the pH of alkaline soils.

Remember it is difficult to maintain acidic soil if it is naturally alkaline and vice versa. Soil will revert to its natural state as the plant absorbs the nutrients you’ve added to make it acidic or alkaline. This means you will have to add soil amendments to your garden every season to maintain the desired pH.

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Please note that this is intended as general information only. Ask one of our qualified horticulturists for more specific advice for your situation.