Measuring the pH of soil / soilless runoff

How to test the pH of your soil mix

Measuring the pH of soil is just as important as with hydro applications, but few people know how to test soil pH to see if it is within the optimum range for growing robust healthy plants. Here I will try to explain my method of testing any soil / soilless mix, enabling me to spot any problems and correct them if necessary.

Firstly, wait till your soil has dried out and is due for its next watering schedule. Then take some plain water that you usually water your garden with, and adjust the pH to 7.0. You must make sure that you know the exact pH of the water going into your soil, and the neutral 7.0 is best, but anywhere from 6.5 – 7.0 will suffice.

Then place your pot into a bowl of some sort to catch the runoff water, and then start to water your soil slowly (with your pH- corrected plain water) till the water starts to drip from the bottom. It’s the first drops of water that will give you the best reading of your soil, so make sure to water slowly till you see the first droplets. Then remove the pot from the bowl to eliminate excess water entering the bowl. Then perform the pH test on the runoff and compare it too your initial test.

The results of the runoff test will likely be lower than your starting value of 7.0. If this is the case, a small drop of 0.5 pH to 6.5 pH (example) would be ok and your soil needs no further alterations at the moment. But that’s not to say that it won’t need any future tests at all, just not at this time.

[Editor’s note: It may be beneficial to obtain an initial sample, as well as a ‘full flush’ sample in seperate bowls. In addition, test several plants in the garden just to verify your results]

What if the pH is off?

If your results prove to have dropped considerably, say to around 5.5 (which can happen in late stages of flowering), you will need to add some lime into your soil to help buffer the pH back up again.

Remove the first inch or so of soil, taking care not to damage any roots whilst performing this task. Then sprinkle the lime into the pot, nice and evenly at a rate of 1 teaspoon (5 ml) of lime per gallon of soil. Then replace the soil you removed earlier, and saturate the soil good to wash in the lime.

Do the same test next time your plants need watering just to check that everything is fine, if more lime needs to be added then just repeat the process again till you reach close to 6.5 – 7.0 with the runoff.

Ensuring that your pH is correct should be done throughout the life cycle; this will help eliminate any nutrient lockout that may occur. I recommend doing this once a month just to keep the PH in check, and you should never have a problem with deficiencies caused by pH lockout.

5 comments to Measuring the pH of soil / soilless runoff

  • richard

    Quit rare i think… i’m now checking my plants there runoff and they are at ph 5.5…very low for a soil grow i think but i don’t see any decencies or problems occurring…
    Ec is also quit high around 5.4 but my plants are looking very healthy?!…
    Is this normal because i want to bring them in to flowering stage but i’m considering to flush them until my Ph is balanced again to 7 and then ad back nutrients with a correct Ph level.

  • Anonymous

    I checked pH of my nutes water mix and it was 6.5 going in, runoff tested 5.5 a lite orange on the color code chart. Am I still good or do I need to raise the ph in my soil? Thanks in advance

  • Danny

    That’s called “soilless”, Justin. It is hydro.

  • Justin p

    Ok fine, why is it always the assumption that the ph drops, I’m confused, it’s explained in detail how to trap the run off, and vaguely explains what to do if it’s lower although never in enough detail, heaven forbid if your ph seems to have risin cause I haven’t found squat on that. I’m obviously doin something wrong just not sure what it is and exactly how to cure, I’ve countered the feeding and waterings with a lower ph reading and still haven’t changed the medium, that’s the other thing I haven’t been able to figure out: I run what I guess everybody would consider a soilless mix, somewhere like 3 parts sunshine #4, 2 parts coco, 1 part air stone. So tell me is that considered soil? I thought it wasn’t, so then that would mean its hydro, and if that’s the fact my ph is way out to lunch!!.. Just really need some straight up schooling, thanks for any help! Can’t imagine I’m the only one had to deal w this cause I haven’t came across much lending to my problem.

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