How to Test Soil pH

pH is a measurement of how acidic (1), neutral (7), or alkaline (14) something is. We care about this in gardening because soil pH affects how well our plants are able to uptake nutrients through their roots. Many of our plants do best near a neutral pH, around 5.5-7.5. Common exceptions include blueberries and potatoes, which can handle very acidic soil.

Many Australian soils tend to be on the acidic side of the spectrum, while raw manures are slightly alkaline. Understanding what you are working with from the start will allow you to slowly shift the soil in the right direction. Organic compost, for example, is neutral and will help to bring any garden back toward equilibrium. 

There are plenty of instruments to measure soil pH and even more people that will be happy to sell them to you. It's a bit like when you go to a 4WD store looking for a road map, only to walk out with a GPS system. Both will get you there, it's just a matter of how much uncertainty you can tolerate. For our purposes, we just want a general idea and a simple soil pH test kit is perfect.  

Start by taking a tablespoon-sized small soil sample from at least 10cm deep. This will prevent any surface dressing or mulches from impacting the measurement. Discard any stones or roots and place the sample on a clean surface, most kits will include a plastic card for this purpose.

Add indicator dye to your sample and mix together until a thick paste is formed. The key is to get an even distribution of dye through the sample.  

Add white powder (barium sulphate) to the mixture and gently mix through. Let the sample sit for about a minute.

Compare your sample to the colour card provided. Results are most accurate within the first few minutes (just like a preganancy test), so don't dilly dally. 

Soil is slightly acidic, about 6.0, but well within the threshold for our kale seedling. We've mixed organic compost into the bed and will check pH again at the end of the season. With time and a little effort, we will gradually improve the soil, but few changes will happen overnight. There's probably a life lesson in there somewhere.

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