Urban Food Garden

Testing Soil pH

Testing the pH (measurement of acidity or alkalinity) of soil is an important tool in managing a vegetable patch.  This page looks at how soil pH affects plant growth and the different ways to measure it.

How soil ph affects plant growth

Plant nutrients become available or unavailable according to the soil’s pH level.  Most vegetables thrive on a slightly acid soil.  However, some prefer slightly alkali soils while others need very acidic soils.  It is not that the nutrients aren’t present in the soil, it is just that if the pH of the soil does not match the plant’s preferred soil pH range the plant will not be able to absorb the nutrients. 

Chart showing how soil pH affects the availability of plant nutrients.  Chart courtesy of the World Wide Web.

Soil ph test kits

There are several soil pH test kits on the market.  They all involve mixing soil with water, adding dye that changes colour according to the pH of the soil, then comparing the colour of the soil with a pH soil colour chart.  While I used a soil pH test kit for a number of years I found them to be fiddly and messy to use.  Consequently, I generally did not do as many soil tests as I should have.  I no longer use a soil pH test kit.

Manutec test kit, which is the one I used in the past.   Images courtesy of the World Wide Web.

Soil pH meters

There are a number of soil pH meters on the market, ranging from cheap home gardener models all the way through to professional quality meters used by foresters and farmers.  They can also be divided into two types of meters, analog and digital.  The analog meters do not require a battery while the digital ones do.   Note that I have only ever used analog pH meters.

My first soil pH probe was a cheap home garden one. While it was much easier and quicker to use than a soil pH test kit I was concerned that it might not be that accurate.  I eventually bought a more expensive professional standard Kelway soil pH meter (see details below).  However, while the Kelway is likely to last longer and is easier to read, my comparative soil pH tests showed that the cheap home gardener meter was just as accurate as the more expensive Kelway meter.

TOP: Kelway Soil pH & Moisture Meter.  This is a professional standard Ph probe used by foresters and farmers.  As such it is expensive, costing around $200 AUD.  BOTTOM: Generic home gardener Ph meter, readily available from nurseries for about $15 AUD (August 2021 prices).

Soil pH test comparison between my home gardener and Kelway professional meters.  While the Kelway meter is slightly easier to read the cheap home gardener meter was just as accurate. 

Using a pH meter
  1. REMOVE ANY LARGE STICKS OR CLODS OF EARTH FROM THE IMMEDIATE AREA TO BE TESTED
  2.  POUR SOME WATER ON THE SOIL AND LET IT SOAK IN FOR A COUPLE OF MINUTES.
    It is recommended that distilled or tank water be used, but you can also use mains water if its pH is fairly neutral.
  3. WIPE THE METER’S PROBE WITH A CLEAN RAG
  4. INSERT PROBE INTO THE GROUND AND WAIT UNTIL THE NEEDLE HAS STABILISED BEFORE TAKING A READING.
    This usually takes no longer than 20 seconds.  The depth that the probe is driven into the soil should be no deeper than the length of a hand trowel.
  5. WIPE THE PROBE CLEAN BEFORE STORING THE METER IN A DRY PLACE.

This photo is for demonstration purposes only.  When testing the soil’s pH the water is poured onto the soil and left to soak in for a couple of minutes before inserting the meter’s probe.

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