What Is Soil pH And Why It Matters


Much like baking a cake at the right oven temperature, what is classed as the ideal soil pH level all depends on what you’re hoping to plant this season.  

Soil is made when rocks break down and mix with plant and animal matter. The properties of your soil are largely determined by the amount of organic material it contains, as well as the type of parent rock it comes from. While the types of materials found in your soil will all contribute to determining the pH levels found in the earth, it’s also been proven that particular agricultural practices can also significantly alter soil pH levels – but why does this all matter? 


What Is Soil pH And What Does It Do?

If we’re going to get technical, soil pH stands for “potenz Hydrogen” – meaning the potential to be hydrogen. The pH scale ranges from zero to fourteen, and is designed to show how acidic or alkaline the soil is. 

Soils can be classified according to their pH value:

  • 6.5 to 7.5 – neutral
  • Over 7.5 – alkaline
  • less than 6.5 – acidic, and soils with pH less than 5.5 are considered strongly acidic.

Acid sulfate soils can have extremely acidic pH values (pH less than 4).

In higher rainfall areas the natural pH of soils typically ranges from 5 to 7, while in drier areas the range is 6.5 to 9. For the average gardener in Australia, the ideal range for most plants sits between 5.5 to 7 on the soil pH scale, although this can vary depending on the variant of plant. An example of this is blueberries and azaleas prefer a soil pH level that is more acidic in nature, whereas varieties such as lilacs and clematis prefer a more alkaline level. 

Soil pH levels need to sit at the appropriate range in order for plants to absorb the nutrients provided in the earth while managing the more toxic contents. The bacteria distribution also helps to release nitrogen contained in dead and decaying matter in the soil, which is crucial for healthy plant growth. 

How To Measure Soil pH Levels

If your plants are happy as they are, then there’s a good chance that your soil pH levels are already sitting at the optimum neutral range. However – and this often depends on where you live – you may notice a soil pH imbalance. Your plants may look sickly, not develop at the standard rate, and it’s usually down to one of the following:

  • aluminium toxicity
  • manganese toxicity
  • calcium deficiency
  • magnesium deficiency
  • low levels of essential plant nutrients such as phosphorus and molybdenum

With a large range of pH soil kits now available in Australia, determining the qualities of your soil is relatively easy. A handful of these include:

Water Test – A tried and true method is to simply pour water onto your soil directly. If it drains quickly, it is likely to be sandy or gravel soil, compared to clay which takes longer to absorb. 

Squeeze Test – Softly compress a handful of soil in your fist. If it’s sticky and stick to touch while remaining relatively intact, it’s clay. Sandy soil will instead feel gritty and crumble easily. Silty soils will feel smooth and hold their shape for a short period of time. 

Settle Test – Add a handful of soil to a clear container with water. Shake well, then leave to settle for 12 hours. When you return, clay and silty soils will leave the water cloudy, with a layer of particles at the bottom of the container. In comparison, sandy soils will leave the water mostly clear, with the exception of a small particle layer at the base. 

Acid Test – A normal pH reading is between 4.0 to 8.5, with the optimum range being between 6.7 to 7 for plants to thrive. pH tests are available for purchase at Bunnings or most garden centres in order to test the levels of acidity and alkaline in the soil. 

Soil Test Kit – If you really want to get into the nitty gritty, a soil test kit can assess both pH levels and primary nutrients present in the soil (nitrogen, phosphorus and potassium). You’ll then be able to determine the exact conditions for fertilising and other additions to your garden.

While the above methods are relatively quick and easy ways to essentially ask your soil what it needs – what do you do once you have that data?

The use of plant probiotics will provide invaluable microbes and nutrients that can assist in soil regulation. Ultimately, you’re trying to protect against drought, frost and wind conditions, regulate pH levels, plus give the soil the head start that it needs in order to be at it’s best before new plants are introduced. 

When in doubt, it never hurts to speak to a professional soil doctor. Bioweed are proud to work with their very own team of in house agronomists, so please contact us if you would like to discuss using plant probiotics or the overall health of your garden or soil.