pH – How do I test and change it?

This is part two of a two part series on pH. If you haven’t read part one already, I highly suggest reading it first here. It explains exactly what pH means and how to interpret it for your plants.

Don’t forget to check out my personal hydroponics growing diaries here and join me on my adventure!

Now that we all know what pH means, let’s jump right into what to do next.

As you’ll remember from the last blog post, I explained how different plants require different levels for optimal growth. I’m going to walk through step-by-step how you would go about setting up your soil or water for your desired pH. As an example, I will use lettuce throughout this article as it’s one of the most commonly grown hydroponic plants. These steps will work for anything else you might desire to grow as well.

Step 1: Test your pH.

There are many ways to do this, but today I’ll only be covering the main two ways; Digital or chemical.

Digital pH meters are by far the easiest to use and the preferred method for hydroponics. You can purchase them at any hydroponics/aquarium store, or even on eBay for a few dollars. You simply insert it into the water, and let the reading stabilise!

Chemical pH test kits are perfect for soil, but not ideal for liquid based systems. Always refer to the manufacturer’s instructions for your specific test kit. Basically, you take a sample of soil from your desired area and apply a few drops of the pH dye. It will change colour based on the pH levels. A chart will be provided where you can compare the colour and read your pH. This can be problematic for hydroponic systems as the water may already be coloured due to nutrients.

Step 2: Change your pH.

Hydroponic Method: (Scroll down for soil)

Okay, so now you know what your current pH levels are. For my lettuce example, let’s say I tested my hydroponic nutrient mix at 7.5pH. GTG Hydroponics has an amazing chart which you can find here. Lettuce grows best in a pH between 6.0-7.0, meaning my water is too basic for the lettuce to grow well. No need to worry, though, as fixing pH in a hydroponic system is incredibly easy.

Simply purchase some pH down or up (depending on if you need to raise or lower your pH). Many different brands make this, although General Hydroponics is the most widely used. Once you have it, read the instructions on the back of the bottle for the exact amount you need to put into your solution – this will change based on how much water you’re using. Once added, stir the solution making sure it’s well mixed, and repeat the pH test. If you find it’s not quite there yet, add a little more.

The key is to only add a little at a time. Less is better! You can always add more, but if you add too much you might need to use the other compound to fix it. You’ll be surprised with how little you need!

Soil Method: (Scroll up for hydroponic)

Adjusting pH in soil is a lot more difficult and time consuming than hydroponics, but it can still be done. I’d always recommend starting with potting mix as it’s usually balanced around pH 7 which is close enough for most plants. If that solution doesn’t suit you, there are other options.

To lower pH (make the soil more acidic), add sulphur or aluminium sulphate to your soil and spread. Read directions on the back of your specific product for exact quantities.

To raise pH (make the soil more basic), add lime to your soil and spread. Read directions on the back of your specific product for exact quantities.

Make sure to lightly water in the powders after applying them to make sure they settle into the soil and don’t just blow away! After application, it can take anywhere from a few days to months to change the soil pH (depending on soil type, area, etc.). Test the pH regularly until it stabilises where you want it to. As you can see, this is very time consuming so you might find it better to just use potting mix as well.

Now you know how to test & change your growing medium’s pH! Combined with your knowledge from the last article, you should be ready to go out and tackle your gardening problems head on. Good luck, and happy growing!

This is part two of a two part series on pH. If you haven’t read part one already, I highly suggest reading it first here. It explains exactly what pH means and how to interpret it for your plants.