pH soil acidifying with battery acid?

girlfromthegarden(z5 Indy metro)May 2, 2006

Thought I'd doublecheck with you all, since it's not something I've come across recently here - use of battery (sulfuric) acid found at auto parts stores, etc., for lowering water pH when adding to blueberries, pawpaws, etc. - ??? I was advised to use this by the gentleman who sent me two of the four pawpaw seedlings I acquired this spring, for keeping the soil more acidic. Elsewhere I've read you can buy this acid, but don't know how safe it is to handle, and what's a recommended dilution if tap water tends to be pretty hard/alkaline (tbsp/gallon type of ratio would be helpful). Vinegar is cheaper but, as my dad (former chemist) says, is a fairly weak acid - anyone know the difference between obtaining roughly the same lowered pH in a gallon of water using either of these? (I'd be using for watering blueberries in containers, too, so recommended concentrations might differ depending on whether the water's going to be poured into a pot vs. onto the ground around a pawpaw.)

If vinegar is safer and just as effective, then I won't mess with battery acid, but wanted to hear from wiser heads first.


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thisbud4u(San Diego)

My local USDA agent who grows blueberries just got a huge vat of sulfuric acid for adding to the irrigation lines---at some huge dilution, of course. I'm not sure at all what dilution is needed (maybe ask a USDA extension agent), but I know at least that it IS used. He said that commercial blueberry growers also use it. However, it is most certainly NOT safe to handle. One little splash in the eyes and you're talking about a seeing eye dog and a cane. The other question is, how pure is this sulfuric acid used for batteries? If it contains heavy metals or other undesirable impurities, it could spell death to your plants. If it's pure, 100% sulfuric acid, it would work, if you're able to come up with the right dilution, and if you're willing to deal with the risks.

    Bookmark   May 2, 2006 at 2:03PM
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Please do not fiddle around at home with sulphuric acid. It is just too dangerous and caustic. There are many alternatives for lowering Ph like garden sulphur, iron sulphate, and organic mulches. Use something like that.

Don Yellman, Great Falls, VA

    Bookmark   May 2, 2006 at 2:10PM
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girlfromthegarden(z5 Indy metro)

thisbud4u and Don - thanks, I definitely want to *avoid* anything possibly dangerous, since I'm leery of even using the drain opener chemicals that are required to unblock the shower drains at home (necessary evil). Most of what I've read makes it sound like battery electrolyte is a diluted sulfuric acid solution rather than full strength (but don't know its concentration or purity unless I actually saw a label, haven't checked it further than here for advice). Per what you said, I do use other soil acidifiers (elemental sulphur, Hollytone fertilizer, iron sulfate, pine needle mulches, etc.) but since there's not always an adequate abundance of stored rain water (I do try to catch it from the downspouts during a torrential thunderstorm, even if I end up looking like a drowned rat!), I really do need to "sour up" the tap water that I use for watering during hot weather, it's simply too "hard" to put on straight or it'll raise the pH in the containers fairly quickly. The pawpaws will get rainwater mainly but while young and establishing themselves, they'll definitely need extra water once we heat up in a month or so here in Indiana. The vinegar-water solution worked decently enough last year, but honestly I don't know how low it would take the pH of the water I'm using since acetic acid is a weak acid and tends to not have much ooomph even if you used nearly straight vinegar (per what my dad told me). Hence the query about whether using a stronger acid (carefully) would be good for making a heftier "sour" water solution for the acid-loving plants. With pH, it always feels like you can un-do all the effort of adding one ingredient for lowering the soil acidity, by not thinking of how high the alkalinity is with the water you're using (often daily during really hot weather). I saw something else (can't remember where) about using citric acid (isn't that vitamin C?) for the same purpose, but how cost-effective is that? at least vinegar is a no-brainer, just a few glugs from the jug and I can even taste-test the tartness of what I'm pouring out. Something I would NOT try with battery acid!


    Bookmark   May 2, 2006 at 2:46PM
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Part of the problem with using sulfuric acid, which is what I believe is used in batteries, is that it's completely unbuffered- its acidity cannot be "stored" in a chemical package to be released in a measured way. More acid equals lower pH with the "mineral" acids, particularly. But with a buffer "more" means "the same power, only longer".

Soil amendments that modify pH are usually buffering by nature, so they won't be washed away by the first irrigation. To use those strong acids you'd want to have a way to continuously add tiny amounts.

My wife bought a gallon of VERY strong acetic acid (vinegar acid) the other day to use as a weed killer, and I thought it was pungent enough to warrant extra care. Do be careful with any of these things, as inhalation can be inadvertent and very, very serious.


    Bookmark   May 2, 2006 at 3:38PM
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fruitnut Z7 4500ft SW TX


I've had the same thoughts as you since my blues are in pots and it hasn't rained here since Oct, not even 0.01 inch! My well water is very hard and have been adding one gallon of 4% vinegar in 30 gallons well water. That probably does next to nothing. But even if I got sulfuric acid won't know how much to add to the water without purchasing a ph meter. Have read about people acidifing their irrigation water to ph 5.5. In CA they have commercial applicators who apply sulfuric acid prior to planting blues. After injecting the acid into the soil they flood irrigate. This supposedly lowers the ph to the desired level in about the upper foot of soil.

The southern highbush that I have seem pretty tolerant of questionable soil conditions. So unless they start looking worse, I'll stick to the vinegar and add acidifying agents to the pot like ironite and ammonium sulfate.

The Fruitnut

    Bookmark   May 2, 2006 at 3:59PM
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Concentrated sulfuric acid has appearance and viscosity similar to corn syrup. To handle it safely, you must have an acid resistant apron, rubber boots, appropriate gloves, and a splash shield protecting your face. If water is added to a container of concentrated sulfuric acid, the water will turn to steam, causing the acid to erupt and possibly fracture the container. If concentrated acid is carefully added to a container of water, the heavier acid will mix with the water as it flows down to the bottom of the container, and the solution will heat up, but not erupt. I have never used sulfuric acid on our blueberry patch, but I do use standard food grade white vinegar, about 6 fluid ounces, per 4 gallons of tap water, to lower pH. Our tap water has considerable dissolved lime.

    Bookmark   May 2, 2006 at 10:43PM
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jblaschke(8b TX)

Even the sulphuric acid you can buy at pet stores to lower pH in aquariums comes plastered with dire warnings. Better to go with soil additives such as garden sulphur.

    Bookmark   May 3, 2006 at 1:43PM
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The problem with acetic (vinegar), citric, or other organic acids is that they are not long-lasting anions. As soon as bacteria in the soil biodegrade them, you lose their acidifying power. So for long-term soil pH management, they're pretty much useless, unless you were to use them often.

    Bookmark   May 3, 2006 at 1:54PM
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fruitnut Z7 4500ft SW TX


They won't last in soil , but if you add vinegar to water containing calcium carbonate, will the carbonate be neutralized? I guess it would be 2H + CO3 = H2O + CO2.

Then the water could set in a barrel until used.

The Fruitnut

    Bookmark   May 3, 2006 at 2:11PM
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Fruitnut, I like your reaction diagram, but you forgot about the calcium. After the carbon dioxide has evaporated into the atmosphere, there remains calcium in the soil. This is not a theoretical discussion for me, we have a lot of lime in our water, and I have been using white vinegar to lower pH before watering the blueberry shrubs as needed during the summer drought. I am concerned about the long-term effects of this practice.

    Bookmark   May 3, 2006 at 4:09PM
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Batteries have lead sulfate dissolved in the acid. I do not know whether any exists in the new acid for adding to batteries but I'd certainly make sure it did not. Some hardware stores and such sell a sulfuric-acid drain cleaner/unplugger, which would probably be chemically safe if not physically safe. I deal with full-strength sulfuric acid and even if I pour just an ounce or so into a 55 gallon drum I hear it boil into steam for an instant. NEVER let water go into the acid, always visa versa, as was said by another, and always with a superabundance of water, NOT 50:50 say. I could get 55 gallons of limestone aquifer water to well below pH 4.5 (my target) with just a couple ounces (I don't know exactly as I used metric, about 40 mL if I remember correctly). Sulfuric acid would turn any calcium carbonate (above what simply dissolves) into harmless gypsum.

    Bookmark   May 3, 2006 at 4:55PM
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Alkaline irrigation water has Calcium, Magnesium, and/or Sodium as the cation for the carbonate, and as ericwi points out, they don't go away in this reaction; rather, you make the acetate or citrate salt of them. You have temporarily lowered the pH. But in the soil, bacteria will oxidize away the organic anion, and the soil pH will tend to rise again. Yes, it acidifies your water temporarily, but I'm not sure there's any long-term advantage in that, since the alkaline cations are still there.

    Bookmark   May 3, 2006 at 9:21PM
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fruitnut Z7 4500ft SW TX


Thank you, I understand what you are saying. I'm going to hope it rains so I can use rain water. I think the southern highbush that have survived in my pots while others expired are pretty tolerant of high ph. Star, Santa Fe, and Southmoon have done great for me and the fruit has been very good this spring.

The Fruitnut

    Bookmark   May 3, 2006 at 11:07PM
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fruitnut Z7 4500ft SW TX

We're in another long, two month, dry period and I'm out of rainwater. I have about 90 gal of rainwater storage for my three potted blueberries. That's enough to last 1-3 months depending on season. So I checked at the auto parts store and could buy a qt of battery acid for $4.35. Found on the net that battery acid is 33.5% sulfuric acid. So figured it couldn't cost more than a few bucks, an eye, and some skin to try this out!

First I diluted the quart by slowly pouring it into a 2.5 gal plastic container of water. It wasn't really pouring, as in splashing, as there was a plastic tube to pour it thru, no splashing. That was a piece of cake by following the instructions. The container of water didn't heat up noticably. I now had a solution containing 3.3% sulfuric acid...safer and easier to handle than the battery acid.

Then cleaned my largest plastic rain-barrel, 50 gal, and filled it with well water. Added 100ml at a time while checking ph with 4.0-7.0 pH indicator strips. It took 900ml to lower water pH to 4.7. Checked it again after 8hrs and it was the same.

Really think this was pretty easy and a much better solution to the hard water problem than vinegar. I got the indicator strips from, 100 strips for $15 including shipping. They are good strips and much easier than buying a meter that needs calibration.

The Fruitnut

    Bookmark   March 20, 2007 at 3:59PM
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I was a chemistry major and I did some internet searches after reading the posts.
There is information on using sulfuric acid with caution, and Don's advice on alternatives is prudent. Hard water or lime-rich soil can require 5 times more acid than soft water.
Perhaps one advantage of acetic acid is that it dissolves insoluble calcium salts and if water is abundant they will leach away. So sulfur and iron sulfate amendments and occasional vinegar treatment may work for most situations. A website with info is listed.

    Bookmark   March 21, 2007 at 7:45PM
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I tried what you proposed a few years ago. Aside from all the handling problems, one also needs to have a good set of tools for measuring pH, plus the math skills to properly determine the required volumes of acid. Unless you have a fairly sophisticated workbench and irrigation system, it isn't worth the trouble.

    Bookmark   March 25, 2007 at 11:27PM
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thistle5(z7 VA)

At the garden center where I work p/t, we have 2 soil acidifiers (1 from Bonide, I don't remember the other one),as well as sulfur, Hollytone,iron sulfate,etc.- depending on the amount you need, I'd do a cost comparison-it might be simpler to buy a garden product, rather than do the math & use the battery acid.

    Bookmark   March 26, 2007 at 5:59PM
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I live in an area that is largely lime stone and clay so my soil has a very high PH level. I have tested the soil at 6.7 to over 7.0 ph I planted a Pin Oak tree and after two years it started turning yellow. I found out it was caused by a high soil ph. After doing more research I found out that a Pin Oak tree requires a very acid soil, even more so than a white or red oak tree. Also unlike a red or white oak it loves a moist soil. I tired adding 10 pounds iron sulfate to my soil to reduce the ph but after 5 months of taking readings I only lowered the ph to 6.0 Getting desperate I read about using battery acid to lower the ph of the soil. Also reading that a soil rich in lime and clay would require a lot more acid than a soil low in lime would, I headed out to my car parts store and purchased 5 gallons of battery acid for about $25.00. This acid is a sulfuric acid solution of water and sulfuric acid making a solution of 33.5% acid. Following the advice of my garden canter specialist I put 3 gallons of pure solution into my watering can and watered the ground around the tree (about a 10 foot circle) then I got out the water hose and soaked the area for almost an hour so I had standing water about 2" deep. I let that settle overnight and the next day took soil readings around the tree. My soil read 3.7 to 4.5 ph all around the tree. With luck and a few weeks I hope to see my rich green leaves again. Now understand that 3 gallons of battery acid is a very large amount, but again I live in an area of lime stone and clay with very hard water so the soil was able to tolerate the large concentration of acid. I would strongly recommend using some of the techniques stated above by mixing the acid with water to get the proper ph solution your looking for.

    Bookmark   June 21, 2008 at 6:59PM
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I've regularly been using new battery acid on my contaier blueberry plants for over 2 years now, and the plants are doing beautifully. I have about 30 highbush berry plants/ It took a short amount of time to get my formula down, but now it is very easy and the same every time.

I live in SoCalifornia and our water pH is about 8. Using great care, I add 2 cups of new battery acid to water in a gallon container almost full, and then top it off with water to full. That is my stock solution. (always add acid to water). Then I add 2 cups of that to a 32 gallon garbage can, and water my plants with that. I also add about a half cup of sulfate of ammonia to each garbage can full of water. I use a bucket to distrubute the treated water.

My plants are large and lush. This is what has been working for me.

    Bookmark   July 11, 2009 at 12:11AM
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a very safe alternative is n-phuric acid, a combination of concentrated sulfuric acid and urea created in a factory. The combination of the two removes the danger of handling conc. sulfuric acid (will cause severe burns by desication) and still delivers strong soil acidification. It's available at any commercial farm supply store such as Western Farm Supply or Crop Production Services. I applied 10 gallons onto 300 square feet of soil before planting blueberries, very successful

    Bookmark   August 18, 2011 at 5:44PM
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