16 Jul 2019

The Importance of pH – focusing on the basics

by | posted in: Gardening | 0

It is very easy to forget some of the basic things that help us understand what is going on in our soil.  Testing the pH of your soil is one such activity. Checking pH can be done through a very simple ‘in the garden’ test.  pH test kits are easy to use and all gardeners should have one. You can also purchase digital meters that will read soil pH, however I do like using the testing kit.  The collection of the samples, mixing in the liquid, applying the powder and watching the col […]

It is very easy to forget some of the basic things that help us understand what is going on in our soil.  Testing the pH of your soil is one such activity. Checking pH can be done through a very simple ‘in the garden’ test.  pH test kits are easy to use and all gardeners should have one. You can also purchase digital meters that will read soil pH, however I do like using the testing kit.  The collection of the samples, mixing in the liquid, applying the powder and watching the colour develop is a nice little scientific process that can still make me feel like a “grown up.”
pH is a measurement of the power of hydrogen (hence “pH”)  and this dictates the acidity or alkalinity of the soil. It is measured on a scale from 1 (extremely acid) to 14 (extremely alkaline) with 7 being neutral. Both extremes are damaging to plants, which generally prefer values between 6 and 7.  Soil pH affects nutrient availability; microbial activity, biological processes and impacts on decomposition rates of organic matter. Incorrect pH can conspire to restrict root growth and limit access to water and nutrients.

If you are concerned about productivity in your garden; how your plants are growing or not growing; or any other aspect of your plants or soil that just don’t seem quite right, check your soil pH before taking any other steps.  If a pH test indicates your soil is either too acid or too alkaline there are remedial steps you can take to help rectify the problem. 

It is much easier to amend a garden plot prior to planting.  However if you need to amend a plot that is already planted ensure that the mineral you are using does not touch your plants and mix into the top few cm of your soil.  Give the garden a good hand water after applying your amendment.

Decreasing the Soil pH

Acid soils with a pH of less than 6 commonly have deficiencies in:

  • Calcium
  • Magnesium
  • Phosphorus
  • Potassium
  • Molybdenum

In Alkaline soils with a pH of more than 7 the following nutrients may be unavailable:

  • Iron
  • Manganese
  • Zinc
  • Copper
  • Boron

https://greenharvest.com.au/GreenGardenNotes/UnderstandingSoilpH.html

Increasing the soil pH
Amount of Sulfur per 1 square metre
needed to lower the soil pH to the
recommended level:
Present pH         Desired pH
6.5          6.0         5.5
8.0             136g       181.5g     227g
7.5              90g        136g       181.5g
7.0              45g         90g       136g
6.6                              45g        90g    

It is easier to change pH on a sandy soil than on a clay soil.

Sandy soils  1k to 10 sqm is estimated to increase pH by 0.5 – 0.7 
Loam 1k to 10 sqm is estimated to increase pH by  0.3 – 0.5
Clay soils 1k to 10 sqm is estimated to increase pH by 0.2 – 0.3