Tap water pH

TT, zone 5b MAJanuary 9, 2011


x has piqued my interest in this now...what is the ideal tap water pH for C & S? Is there a general range that is better to be in?



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Have you read the article by Elton Roberts? it will tell you all you need to know

Here is a link that might be useful: Cactus_and_Alkalinity.pdf

    Bookmark   January 9, 2011 at 12:32PM
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TT, zone 5b MA


1 Like    Bookmark   January 9, 2011 at 12:50PM
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Nutrient uptake by plants works best at a pH of about 5 to 6.

The net pH of the water in the pot is a result of the chemical properties of both water and soil, so I measure the pH of water that runs out of the holes in the bottom of the pot sometimes, just to check that it does not deviate too much from what I want (I aim at 5.5-6.0).

    Bookmark   January 9, 2011 at 1:14PM
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greenman28 NorCal 7b/8a

Exactly what TJ said (5 - 6).
Check the effluent from the bottom of the pot.

Test your tap-water, find out how much white vinegar (acid) is required to bring
it into a favorable pH, then add that amount to the water you use in the future.


    Bookmark   January 9, 2011 at 2:51PM
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tapla (mid-MI z5b-6a)

A dear friend sent me a link to this thread because I am recently returned from doing battle at the Houseplant Forum) over the same pH issue you guys are amicably discussing here. I pretty much explained managing pH in container substrates in exactly the same way as the article Caudex linked to, so of course I think the article is spot on. ;-) In my experience, the easiest, and actually the only realistic way for a hobby grower to manage pH, is by managing the pH of the irrigation water. I've long been suggestion that growers who suspect pH induced nutrient issues do as Josh suggested: Add enough white vinegar or citric acid to a given volume of water to bring the pH down to the desired level (for me, it's 5.8-6.0). Make note of it and add that amount of acid to the same volume of water each time you irrigate.

I over-winter a lot of plants under lights, and even though I use a very fast soil that allows me to water copiously, flushing carbonates from the soil at every watering, I sometimes see some pH-induced micro-nutrient deficiencies develop toward spring, evidenced by leaf symptoms. Adding the appropriate amount of acid to my irrigation water has always either prevented the symptoms from occurring, or, if I'd been lax & not been acidifying the irrigation water it always corrected the symptoms quickly.

Just thought I'd let you guys know I found this an interesting discussion that could be of value to a lot of growers if they popped in.

That's my say. Thanks. ;o)


    Bookmark   January 9, 2011 at 3:51PM
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jojosplants(9/ Tucson, Az.)

Hi Guys!
Great Thread!

pH had never crossed my mind when it comes to my cactus and succulents!

I found this to be great reading!
Caudex~ great link, thank you!

I plan on testing my water and see where I stand. A few of my plants just don't look as happy as they should be. :-)

Have a great day!

    Bookmark   January 9, 2011 at 5:56PM
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I never investigated it, but I think that the municipal water supply pH may vary considerably during any given year. Luckily a slight deviation shouldn't matter much, especially cactus and succulents which tend to be more tolerant than other plants.

A topic for another thread: Which species or families benefit most from an acidic watering scheme? Many South American cactus species, especially Rebutia and Sulcorebutia, prefer acidic lives. As do many of the "rare" Mexican species like Ariocarpus, Pelecyphora, small Mamms, etc. The native soils are high in limestone and pH but rainwater is still acidic. Older literature falsely assumes that these plants require additives to create alkaline soils. In reality, they are found in calciferous soils in habitat not because they prefer the rocky soils, but more likely because they drain so well that there is not enough moisture to support other vegetation. Aztekium grow in almost pure gypsum, like concrete when dry. That doesn't mean in cultivation this should be replicated.

Pachypodium brevicaule is another acid lover. Makes you wonder if all the hoopla surrounding so many "difficult" species is nothing more than the potentially bad habit of using tap water.


    Bookmark   January 9, 2011 at 6:10PM
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tapla (mid-MI z5b-6a)

I don't have near the experience that you guys do with cacti & succulents, but I do consider myself a good observer, with something that might interest you.

I have several plants I consider as 'tell' plants, which are plants that simply exhibit micronutrient deficiencies in advance of other plants. One is an Echeveria. My water comes out of the tap at around 8.5 - 8.8, so it's not unusual for a few of my plants to exhibit some pH induced Fe deficiencies. Here's the thing: If I add a little Sprint 138 (an Fe chelate formulated for high pH applications) to my fertigation solution, it turns the plant from pink to a pinkish green (yuk). In the winter, with the plants under lights, if it's pink and I simply lower the pH of my irrigation water, it also quickly turns green again. I look at this as pretty sure indication that the high pH of my water is at least marginally blocking uptake of at least Fe and prolly other minor elements.


    Bookmark   January 9, 2011 at 11:43PM
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It is mentioned in the article by Roberts and Burleigh, but they don't seem to fully comprehend how important it is to expel surplus CO2 when determining the necessary amount of acid (understandable since they are beginners in this field). It can be done by bubbling air through the water with a pump+diffusor used for aerating aquariums, or by intense stirring (less efficient). Simply letting the water stand and wait for the pH to stabilize takes a loooong time.

    Bookmark   January 10, 2011 at 2:31AM
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penfold2(4b, MN)


I use a squirrel cage type paint mixer with an electric drill to aerate my water. It takes about a minute or two for the pH to stop rising. When I'm done, the pH has risen over a full point, so I must have a lot of CO2. I don't know if this is unusual, but it should definitely be considered since it's relatively easy to check.

    Bookmark   January 10, 2011 at 10:45AM
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This is some good reading and provokes some questions that reading your links and posts no doubt answer.

    Bookmark   January 10, 2011 at 12:23PM
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Keith, thanks for the link to the Cactus and Alkalinity article. It raises some interesting questions for me. I plan to test their solution for my water: pH 8.7 with 50-100 ppm CaCO3.

Tjicken, your last comment was condescending, and wrong. Although they might be "beginners in the field", I thought they did a good job of explaining the pH rebound phenomenon caused by the 'surplus' CO2, and actually devoted three pages to that topic. They also tackle the cacti growing in limestone problem, and convincing demonstrate why the 'alkaline' loving species actually do better with acidic water.

Since "the sole use of adding acid is to decrease the bicarbonate concentration", if you know that concentration from water quality reports, you can calculate how much acid is required to neutralize the calcium carbonate in the water. For my city water, this turns out to be 1-2 teaspoons of vinegar per gallon of water. I plan to test this soon, and hope that adding acid to will cure problems caused by excessive alkalinity.

The solution to the alkalinity problem as presented in the article:

Alkalinity correction for CaCO3 (ppm)

This table that will tell you of the amounts of vinegar to add to 5 gallons of your water. It will leave bicarbonate equivalent to 2.5PPM of CaCO3. The final pH should eventually become 5.8 for all of these additions.

CaCO3 (ppm)
TBS vinegar
Initial pH











The equation for acetic acid and PPM alkalinity can be expressed as:

(Tbsp vinegar / 5 gallons) = 0.0307 x (PPM of CaCO3) - 0.0768

    Bookmark   January 13, 2011 at 12:07AM
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Not sure why the extra page was inserted before the table, sorry about the long scroll. There is a obvious type in the first row second column. It should read 1.5 tablespoons, not three.

I had never given this pH issue much thought. It never occurred to me that the pH of many (most) municipalities is purposefully adjusted upwards to slow corrosion of pipes (a sinister government plot (at least from our plants persepective). The 2009 water quality report for my city showed pH in 38 homes ranged from 8.7 to 8.8. That's not a lot of variablility, and makes me wonder if all the samples were not collected on the same day, or week. The CaCO3 level, and water hardness ranged from 50 - 105 ppm. I wonder about seasonal variability. Clearly I need to start measuring pH myself, and making adjustments until I have a stabilized pH a little less than 6 coming out of containers. I'm going to start with a calculated 2-4 teaspoons of 5% acicity vinegar, and see what happens.

Notice above that the initial pH obtained after adding a measured amount of vinegar is much lower than the target of 5.8. This is because of the 'pH rebound phenomenon which happens as the mixture blows off excess CO2 into the atmosphere. The concentration of CO2 in the water will bounce around a little until almost all of the CaCO3 has been converted to CO2, and evaporated into the atmosphere.

If I've got something wrong here, please let me know.


    Bookmark   January 13, 2011 at 3:56PM
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the article in the cssa a couple of years ago said the ph level varied any were from in the fours to in the sixs during a storm so I put a few drops of viniger in a gallon of water and go with that. joe

    Bookmark   January 13, 2011 at 5:48PM
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TT, zone 5b MA

Finally received my pH tester kit today.

Found my tap water (right out of the tap) measured a solid 7 pH. Played with different amounts of white vinegar, and found that 1/2 teaspoon per gallon brought it down to a nice 5.

Next is to test the water after it runs through the pot...


1 Like    Bookmark   January 18, 2011 at 10:20PM
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penfold2(4b, MN)

I have read that trying to control soil solution pH is a pointless task because it is affected by so many variables (temperature, moisture level, etc), that it will constantly be shifting. The best thing to do is probably just to adjust the water itself to a pH of 5.8 (the point at which all alkalinity has been neutralized). Aerating the water, or allowing it to sit overnight, before measuring pH is probably a good idea to ensure that CO2 is at equilibrium with the atmosphere.

    Bookmark   January 19, 2011 at 9:39AM
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Extremely alkaline soil and water here. I do nothing to adjust the ph, it would be too expensive and time consuming to even try. It measures off the scale on any home testing. In theory it should be causing burns.
I have to give iron to a few of the tropicals but other than that no problems. The c/s are the most tolerant.
The c/s on the deck get watered regularly in the summer with tap water simply because on that black roof in full Texas sun they dry out in seconds. Except for a few species that do not tolerate our high humidity I've had no problems with the c/s. You learn pretty quickly what doesn't like high heat and humidity for 9 months.

I understand our water supply here is very difficult for those who own swimming pools.
Good luck with your ph experiments.
Tally HO!

    Bookmark   January 20, 2011 at 1:18PM
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Keep in mind that habitat conditions in which any particular species grows (pH of the soil, etc.) don't necessarily mean that those are optimal conditions for that species. They may just as well be optimal conditions to kill any competing species.

I don't think it's worth playing around with the pH unless you're trying to grow bloated, unnatural plants.


    Bookmark   January 21, 2011 at 5:52AM
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Modifying the pH should not lead to unnatural looking plants. They can absolutely still be grown "hard", colorful and compact.

A reduced pH improves nutrient uptake and helps to grow a healthier, more resistant plant. "Natural" plants get acidified rain water 100% of the time.


1 Like    Bookmark   January 21, 2011 at 7:44AM
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