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My attempts at adjusting pH (for plants) with vinegar and citric acid

We use well water here, which is a little on the hard side. Tomatoes tolerate it, but most other plants start to struggle once past the seedling stage – I would guess it’s because any buffering capacity in the soil has been overcome and the soil is starting to resemble the pH of the water that’s been used.

In the past, I’ve used a few tablespoons of vinegar when watering blueberries that had started to brown, and more recently when I’ve been too lazy to distill water (it takes so long!), I have used 1-2 tablespoons of vinegar in a 4L watering can for spruce (a random guess that has kept them alive thus far).

Fast forward to today, and I figured it was about time to start getting correct pH levels!

Before I get to the numbers (what amounts of citric or vinegar resulted in what pH levels), I’ll mention how I arrived at them.

I grabbed a digital pH meter from Amazon. This is the common cheap yellow one sold under such highly renowned brands as “Dr. Meter”, “Etekcity”, “Dr. Health”, and “Xcellent Global”. They all look pretty much identical, all have mixed reviews, and the biggest difference seems to be how many packets of calibration/buffering powder they come with (if any). This is what it looks like:

pH meter used for testing
2 of the pH buffer packets that came with the meter

Calibration and why accuracy went out the window quickly

There’s a 6.86 and 4.01 pH packet that you’re supposed to use to calibrate. Add the 6.86 to 250mL (a cup) of water, mix it up, stick the meter in a little and adjust the screw. Then do the same with the 4.01 pH packet with a new cup of water.

I did this with distilled water and had the same issue that others have run into: You could calibrate it at 6.86, but then it was a little off at 4.01 (showed 4.10). Calibrate at 4.01 and it’s off at 6.86 (showed 6.65).

Since plants usually tolerate wide pH ranges like 5.5-7.0, this wasn’t a huge deal for me. As long as I’m not at the min/max, it’s not the end of the world if I’m off by 0.1 or 0.2.

The Numbers!

  • pH of the tap water: 7.5 – 7.7 pH
  • pH of water run through the distiller: 6.1 – 6.3 pH

The distilled water’s just listed for reference. It’s expected to be a little acidic since it absorbs CO2 and forms carbonic acid, getting close to 6 was lower than I had expected. I measured a few times (and a few samples) to be sure.

3.5 – 4L of Tap Water (7.5 – 7.7 pH) with Citric Acid added:

  • 1/8 tsp citric acid: 6.1 – 6.3 pH
  • 1/4 tsp citric acid: 5.3 – 5.5 pH
  • 1/2 tsp citric acid: 4.4 – 4.6 pH
  • 1 tsp citric acid: ~3.5 pH
  • 1 tbsp citric acid: ~2.5 pH

Note that the watering can was filled with tap water to roughly 3.75 L and thoroughly rinsed after each attempt. Measuring out powder is easy too, so I’m fairly happy with these numbers.

Because such small amounts of citric acid have such a large effect, I wouldn’t recommend using citric acid to adjust your pH if operating in “guess mode”. You really need to measure stuff here (and know your original pH) since it doesn’t take much to get into plant-killing territory.

Even with a pH meter, an accidental double-dose or poor measurement could have a drastic effect, so keep that in mind.

3.5 – 4L of Tap Water (7.5 – 7.7 pH) with Vinegar (5% acetic acid) added:

  • 1 tbsp vinegar: 5.8 – 6.0 pH
  • 2 tbsp vinegar: 5.4 – 5.6 pH
  • 3 tbsp vinegar: 5.0 – 5.2 pH
  • 4 tbsp vinegar: 4.5 – 4.7 pH
  • 5 tbsp vinegar: 4.4 – 4.6 pH
  • 6 tbsp vinegar: 4.2 – 4.4 pH
  • 7 tbsp vinegar: 4.1 – 4.3 pH
  • 8 tbsp vinegar: 4.0 – 4.2 pH
  • 9 tbsp vinegar: 4.0 – 4.2 pH (actually 0.07 less)

I was pretty sloppy measuring here since it’s a little cumbersome to pour from the jug of vinegar into a little tablespoon. The difference between 8 and 9 tbsp was really small (0.07), which is why I stopped there. Getting below a pH of 4 wasn’t going to happen without a *lot* of vinegar, and we’re much too acidic for most plants at that point anyway.

The really interesting thing to note here is that things REALLY started to slow down once I hit a pH of about 4.5. I’ve read about spruce being fine at 4.5 and tolerating as low as 4.0. That gives a lot more leeway than I had expected – spruce might be a little tough to over-acidify with vinegar (within reason).

If nothing else, “ballparking” pH with vinegar should be a lot safer than trying to ballpark with a stronger acid, particularly when dealing with more acid-loving plants (spruce/blueberries/etc). I had previously been using 2 tbsp – turns out, they probably would have survived anything up to 9.

Citric Acid and White Vinegar (5% acetic) that were used

Anyway, I’ll leave it at that. This is mainly for my own use, but if you’re reading around and trying to “guestimate” how much you’ll need to acidify your water, hopefully you find something above to be helpful.

However, keep in mind that my tap water is undoubtedly much different from yours. Different starting pH, different dissolved minerals, etc. What brings my water to a plant-happy-place might turn your water into a plant-death-solution, so try to get a hold of some pH testing materials. If that’s out of the question, at least search around to see what results others have come up with 😉

 

20 Comments

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  1. Thanks for this… it also informed me that I could use an inexpensive pH meter to test my well water which is acidic. I have a neutralizer (uses calcium to raise it). I really appreciated your analysis of the CREE vs. VERO cobs as well… quite helpful.

    • Hi. I was just browsing to see if vinegar would quick-fix a pH of about 8.5-9.0 in a small tomato patch.The tom plants are smaller than they should be,but otherwise healthy.Ditto 3 corn plants in the same patch,siblings of 18 others elsewhere in the garden that areabout 4x bigger.I’ve got a chemistry background..your “experiment” was elegant and informative.I’ll apply the vinegar as soon as I log out here. Thanks mate.(I’m in Sydney,Australia)

    • You may not need to neutralize your water, a lot of plants like more acidic environments. It’s definitely a pain where I live, since the water has a higher pH, and I had to lower it’s pH after realizing it was making some of my plants not grow as well.

  2. OHMYGOSH thank you so much for this science experiment! I’ve been scouring the internet for something like this lol. I’ve read everything from “a cup of vinegar” to “half a teaspoon” per gallon of water but no one had evidence to back up their (apparent) guesses! Now I can give my blueberries a quick boost when the well water is wreaking havoc on the pH and I can’t get to the store for some sulfur. Thanks again!!

  3. Dunny Junyon

    Ooops…I should have read this first. Over vinegared my hibiscus and the leaves fell off.

  4. Hi. Thanks for the info. Should have read your article before conducting my own “experiment”. Got almost identical result as yours.

  5. Thank you! The data on reducing tap water pH using vinegar was exactly what I needed, and I found it instantly. Now I’m sort of at a loss since I expected this to take at least an hour…

  6. Great info, many thanks. Saves me doing the same experiment to keep my blueberries happy 🙂

    • Anonymous

      Much thanks for your time and trouble on this issue. Internet recommendations are all over the place. You are methodical scientific approach is just what the doctor ordered! Cheers, Albert

  7. As a newbie,I am learning a few things about ph. U guys r good.

  8. Rev Dr Travis A Foster I, Esq.

    The point he made at the end about everyone’s water being different is very important. Last night I used this as a guideline to lower the ph in my hydroponic system. My reservoir is 12 gallons and was sitting at ~7ph and was aiming for around 5.5. I figured I needed around 20T to get there. I used 18T then checked. My ph solution only works down to 4 and would be an orange color, the solution turned bright red! This is a ph so low there isn’t an indicator for it. I went ahead and used some ph up to correct and it took a ridiculous amount just to bring it up into range. My fault not his. I should have added the vinegar slower and checked along the way. The grow bed has six tomato plants about 6 inches a piece and four pepper plants from 2 to 6 inches all freshly transplanted that day. So far I see no ill effects in the plants but definitely had me worried for a bit!

  9. Thanks, really helpful info. Will be potting up some blueberries soon and no easy access to rainwater so if needs be can have ago At acidifying some tap water, should I run out of rain water. Nice one 🙂

  10. Encourager

    Thanks for the article. I completely forgot our hard well water!!! We have set up rain barrels and will use them exclusively for our raised bed that we have been having so much trouble with. I added way too much manure two years in a row, to the point where moss was growing and water sat on the top. My bad. My pH is over 8, probably closer to 9. N is depleted as is the phosphorus with potassium not even registering on the chart – way too high. Sigh. I bought 20% organic vinegar to kill nut sedge which was in some organic mulch we bought. So have lots on hand. Would that be sufficient to lower the pH???

    • 20% is higher than the common 5% acetic acid that I used, so at the very least you’d have to significantly reduce the amount you use. It’s a situation where a PH tester is ideal. If you can’t get a hold of a PH tester and are left to guestimating, I’d be inclined to try a mix/solution on a smaller area for a while first to ensure the concentration isn’t going to harm your plants.

      If it’s a large raised bed that requires a lot of watering, it could be worth looking into sulfur bags (often found as “garden sulfur”), since they break down over time and acidify the soil. Getting the concentration right can be tricky, but if you start with smaller amounts and test the soil PH every couple months you should be able to get to a point where you know roughly how much to add annually to keep the soil at the desired PH.

      • Encourager

        Thanks Matt. Actually the bed is empty right now, waiting for pea planting…at least it was until I did the soil testing.

  11. Anonymous

    Hi there. Is PH test paper reliable enough to check tap water PH?
    Thank you,
    Calling from Europe ☺

  12. Great stuff. Thanks!

  13. Robert Rowe

    I purchased a 44 gallon garbage can for my rainwater collection. It is softer and its PH is usually 7 which my garden tolerates. When it does not rain for a week I will fill the can with my tap water 7.4 PH. Through research I have found that 2 cups of clear vinegar will reduce my water PH to 6 PH which is optimal for all of my garden plants. Citric acid uses a lot less for my 44 gallons but is hard to find in stores. Vinegar is cheaper and my garden thrives

  14. Anonymous

    Wow ! Nice pH’s Here we can have rainwater with pH 8.5; the tap water is pH 8+ ; The aquaponics bed, ~5yrs old, has pH close to 7.4 this must be because of the organic debris….Now we want to add almond leaves to the fish tank…meanwhile, all the plants which we water with the pond water are turning from yellow-light green to a Dark Rich green Baruch hashem! that made such things to be!

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