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Measure The pH and TDS Of Your Soil Regularly

Measure The pH and TDS Of Your Soil Regularly

When you’re growing marijuana in soil, it is always a good idea to measure the TDS (total dissolved solids) and pH (acidity) of the soil you are using.

Keeping soil balanced with the proper level of pH and nutrients will help ensure that you are growing healthy plants.

One of the positive aspects of growing marijuana in soil rather than a hydroponics system is that soil acts as a buffering system for the water and nutrients your plants have access to. Any mistakes in your TDS or pH levels won’t have any immediate negative effects.

One of the downfalls is that it’s easier for nutrients to build up in the soil, which can cause high TDS levels and lower your pH. The TDS and pH at the root level could differ drastically from whatever values you have in the fertilizer solution you are feeding your plants. Obviously, this can cause trouble.

(Hydro growers read  How and Why to Rinse Your Growing Medium)

Additionally, there are other factors which can determine how the nutrients are being taken in by a growing plant. If it’s chilly in your grow room, the leaves of your plant won’t properly evaporate moisture because of the low temperature.

This evaporation is a key part of the vacuum cycle that draws nutrients up through the roots, and without it, your plant won’t pull in all the nutrients available in the soil. This means that the nutrients will start to accumulate in the soil, lowering the pH around the root system.

High acidity in the roots limits the intake functions of the root hairs, which further exacerbates the difficulty your plant will have absorbing nutrients.

This is an excellent example of how your plant’s environment can become unbalanced, even if the pH and TDS levels in your nutrient solution are perfect. It’s very important to measure pH and TDS of your soil regularly— every two weeks works well. Don’t forget!

Measuring soil levels is very easy so let’s start with the basics. You’ll be mixing a 1:1 ratio of your soil from around the roots and demineralized water (water with TDS 0 and pH 7). Then you’ll let this mixture sit for 24 hours, occasionally stirring. Then, simply filter it and measure the TDS and pH. Voila— the values of your mixture are the values of your soil! For more tips on TDS and pH, be sure to download my free marijuana grow guide.

The devil’s in the details, so let’s go deeper with the step-by-step process you can use to measure the acidity and total dissolved solids of your soils. First, you are going to want to gather together everything you need:

-TDS and pH meter
-Demineralized water (water with TDS 0 and pH 7- you can get this at gas stations or drug stores)
-2 measuring containers (capable of containing at least 6 ounces!)
-4 cloth or coffee filters

To start your test, remove 3 fluid ounces of soil from around the roots and mix it with 3 fluid ounces of demineralized water in one of your measuring containers. Let this mixture stand for 24 hours, but continue to stir it occasionally. This way you will make sure all the nutrients dissolve completely.

After everything in your solution has dissolved completely, pour it through a filter into the other measuring cup. Continue to repeat this process until you have a totally clear liquid. Now use your meter to determine the TDS and pH values of the soil your marijuana is growing in.

The best TDS values fall between 750 ppm and 1500 ppm, depending on the maturation of your plant and the amount of nutrients it can absorb. The pH should be around 6.

What to do if you don’t have the right levels? Maybe your pH is too low. If it is 5.5, for example, you’ll want to raise the level up closer to 6. The next time you give your plant water, use water with a pH value of 6.5. The same method works for TDS levels.

If you need any more advice on growing your plants, my marijuana grow bible is full of useful tips and helpful facts. If you have any comments or questions about this article, be sure to leave them below!


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Comment Section

37 thoughts on “Measure The pH and TDS Of Your Soil Regularly

By Mona on 9 February 2015

What is a good tds/ph meter to get? Is there any particular brand or type that you recommend?

By Smileyoh on 22 March 2016

Blue lab is a great price and very durable

By crizzi on 15 February 2015

What is a good quick way to lower the (Ph) level real quick an easy from a pH level of 8 To a pH level of 6

By Robert Bergman on 17 February 2015

If you want to lower the pH of your soil from 8 to 6, water your plants with pH 4 water and test again. Use pH down to lower pH levels of your water…

By Brock on 23 July 2016

After you water with your adjusted pH and you say check it again… Like next day again… Or 2 weeks later during your suggested regular intervals?
Just want to be clear.

By latewood.ILGM on 25 July 2016


Best thing for you is to join our free grow support forum. Many knowledgable and expert growers there.

When I correctly PH my nutrient solution or water, I do not worry about the PH unless I see an issue with the plant. It also makes a difference whether you are using hydro or soil growing methods. Please join the forum. It is much easier to teach and give grow support there. This blog is not set up for sustaining long term grow support. That is what you need. See you at ILGM

By john henry on 17 February 2015

Is it better to keep pH a little on the high side (6.6-6.7),when feeding with cal/mag,

By Bert on 26 February 2015

Is it recommended to measure TDS or can I measure the EC instead? I found that EC-meters are less expensive and easier to find.
I’ve found a formula to convert those two:

To get an EC value, multiply the ppm reading by 2 and divide by 1000.
Thus, if your ppm is 750:
750*2/1000= 1,5 EC
And if your ppm is 1500:
1500*2/1000= 3 EC

the best EC is between 1,5 to 3 EC

By Pete on 6 August 2015

Peter. More a question than comment. I’m a little unclear on the tds measurements. Is this raised by adding more fertilizers. If the feeding chart suggest say 1/4tsp, but the tds is low maybe between 150 to 300 ppm. How to reach the 800 to 1500 ppm?
Also, when harvesting, is it best to hang with root ball intact or cut stem at soil level?

By bingy man on 27 February 2015

Hail I love growing marijuana so I fell n love with your sight I have a a k strain that I raised outdoors but its not developed properly for the time it was growing can u give me some tips on bringing it up to standard

By dean on 27 March 2015

Love the reads I’m a first time grower and found most of the info brilliant keep up the good work

By David Moody on 3 April 2015

Question? Is 3 fluid oz. soil the same as 3/4 cup of soil, compacted or not?

By Greenleaf on 16 March 2018

A shot glass holds one fluid oz. So the way I understand it is 3 shots of water, and 3 shots of soil.

By Moody152 on 3 April 2015

Did anyone reply about good meter to buy for TDM.

By Smileyoh on 22 March 2016

I love blue lab and great price. I broke a few photos pens of theirs at first due to being stupid on my own behalf but they are cool for me man. The set I have now is atleast 2yrs old

By Tiny on 5 April 2015

Can any body help as I need to know what the ec reading is for week 2 veg an so on!!!!

By Darren on 5 April 2015

Any help for ec readings wk 2veg an so on!!!!!!!!

By tub on 10 April 2015

my ph is 6.4, but my ppm is 108. how can i raise my ppm. thanks for any help

By brian on 3 June 2015

i have some autos outside & the leaves in the middle of em are LIGHT green ? any suggestions ?

By latewood.ILGMl on 25 July 2016


Hard to say without pictures and more info. I invite you to join our grow support forum. We can help you better from there and you can add a picture in order to allow us to see the issue instead of guessing. OK?

Happy growing. lw

By Hammer on 31 August 2016

Since discovering the ILGM Forum .I have found a wealth of answers ,and questions ,HA.. It was like finding the missing puzzle pieces to a puzzle that i have worked on for Years.. Excellent staff .Support net work .And helpful hint’s in my email’s from Robert. Not to mention The high quality of Berman’s Lab.. Plus you get access to some of the Strongest genetics out there ,,I am harvesting 3 of the strains available at the ILGM site . And iam VERY impressed and that takes something . But these guys do that sort of thing .. OH YA .. Hammer

By Rex H Johnson on 26 October 2017

Whats a mid priced good soil ph tester

By Hammer on 31 August 2016

One more thing worth the mention ,,ILGM is having a bud of the month contest . Go to the ILGM forum to check it out . Hammer

By Spanky on 7 December 2016

How do I obtain 3 fluid oz of soil from around the roots of my plant?
What is the physical method for doing this? Thank you.

By latewood.ILGM on 8 December 2016


I believe you mean 3 fl. oz. of runoff. This means that you water plant in soiul until excess fluid comes out the drain holes. Collect this “runoff”, and test the PH. I find that checking this runoff is only necessary when attempting to diagnose an issue with your plants. Happy growing, lw

By Greenleaf on 6 March 2018

How does one measure 3 fl. oz. of soil? Or is it 3fl. oz. of run off water. Thanks.

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