pH – What does it mean, and why does it matter?

This is part one of a two part series on pH. Part two explains how to test and modify pH levels. For part two, click here.

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Almost every gardener, soil or hydro, has heard of this unit of measurement. Regardless of it’s popularity, it’s not very well understood. pH, the acronym, means “potential of hydrogen”; but we’re not chemists on this blog, we’re gardeners! So, ignoring what it technically stands for, let me break down what it actually means. Basically, pH is a scale, a unit of measurement like celsius or centimetres. Rather than measuring temperature, it measures acidity. 

Vinegar – I’m sure everyone reading this has consumed some at some point of their life. If I asked you to describe how vinegar feels in your mouth, you’d probably say acidic; and you’d be right! Vinegar usually has a pH of around 2.4 – extremely acidic! Anything with a pH lower than 7 is considered acidic.

Soap – Another easily recognisable item. As you know, soap and all cleaning products usually have that “laundry” smell associated with them. They’re good at cleaning, but just like acids, you wouldn’t want to consume any too strong (for example, bleach, which has a pH of around 12.6). Anything with a pH over 7 is considered basic.

The pH scale ranges from 0 – 14. 0 being extremely acidic, 14 being extremely basic. Now that you have some examples, you should be able to visualise what that actually means. But how does vinegar and soap have anything to do with agriculture?

Plants are kind of like humans – they don’t like things to be too acidic or basic either. 

This chart may look complicated at first glance, but it’s actually very simple. Listed above are all of the main nutrients that plants require to survive. As you can see, when you move further towards the extremes (left/right on this chart), nutrients become less available. Another important thing to note from this chart is that not all nutrients are the same. Iron, for example, is very readily available even at pH levels as low as 4! However, once you go above 8 it’s virtually unusable. Potassium, on the other hand, is the complete opposite – only being available in basic pH levels, and not available in acids. “What does all this mean?”, I hear you ask. There are two main points to take away:

1. Without correctly pH’ed soil/water, plants will not get the nutrients they require and will not grow as they should; they may even die.
2. Different plants require different nutrients. Therefore, they may grow best in a different pH.

Heres a chart from Chanson Water that shows what plants thrive in what pH levels:

So next time you’re ready to plant a crop, check what pH levels you should have in your growing medium before you start! It could be the difference between life and death for your plant.

This is part one of a two part series on pH. Part two explains how to test and modify pH levels. For part two, click here.