Ajusting potted blueberry pH with sulfuric acid and well water

fruitnut Z7 4500ft SW TXMay 9, 2010

Today in the space of 10 hrs we adjusted our blueberry media from a starting pH of 6.8 to 3.8 with sulfuric acid and back to 4.7 with alkaline well water. This is so easy I don't see the need for anything else to get off to a good start with potted blueberries.

Store bought battery acid is 33% sulfuric acid. I dilute it by pouring one qt into 9 qt water. This gives a stock solution that is 3.3% sulfuric and makes it much safer to handle.

It took about two qts of the stock solution mixed in a couple gallons of water leached thru ~12 gallons of potting mix to lower pH to 3.8. Had we been more careful we could have stopped at 4.5 to 5. But having gotten to 3.8 we leached with alkaline well water three times to get back to 4.7.

We'll wait a couple days to see if the pH is stable before using the mix.

We earlier adjusted from 6.8 to 4.4 after planting with excellent results. We used well water adjusted to ~ 3.5 pH to do that.

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The problem with that is, battery acid is not refined, and may contain contaminants such as mercury or lead. It may not enter the plant, but the runoff may pose a mild danger.

You are also tweaking a high PH soil and assuming it will stay that way...it will not. Most revert back towards their original PH on the basis of their makeup. ExampleÂpure peat fertilized with plain miracle grow will test at a higher PH, but will soon revert back.

Better to start with a material close to the desired PH or you will be forced to constantly adjust as commercial blueberry growers do. The reason they choose this method is financial, easier to tweak, rather than remove and replace yards of earth, while on a smaller scale the opposite is often true.

    Bookmark   May 10, 2010 at 4:28AM
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fruitnut Z7 4500ft SW TX

Thanks for the heads up about possible heavy metals in battery acid. That was in the back of my mind. I'll buy some technical grade sulfuric acid to solve that issue. Heavy metals can also be in dry fertilizers like Ironite.

As to reversion of pH. I know that will happen to some extent. But it's not something that concerns me. And it happens with any method of adjusting pH. Just monitor pH and adjust again.

    Bookmark   May 10, 2010 at 8:50AM
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olpea(zone 6 KS)

Mr. Ed,

Do you have any references that store bought battery acid could have significant amounts Pb and Hg? I'm not trying to be contentious, just wondering if there are any reputable sources for the claim.

I bought some sulfuric acid to mix with water for irrigating the blueberry patch and would rather not add lead or mercury in significant amounts. However, I've noticed so many claims of this nature are based on internet hearsay and turn out to be false.

As an example, Fruitnut's mention of ironite is quite correct. It used to contain high levels of heavy metals. However, the company had such bad press and lawsuits they quit making it from mining tailings. Their product is now well under safety levels for any heavy metals.

Still, there are numerous websites warning people against the use of their dangerous product, which no longer exists.

    Bookmark   May 10, 2010 at 11:19AM
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fruitnut: no problem, I am not even sure if blueberries are able to uptake heavy metals. I know they are indifferent to aluminum. Was just wondering about the runoff from the potted plants.

About lead in IroniteÂyes I have heard that. I will not use it because of that fact. It might be safe for a lawn, but suppose next year you want to put a garden there, or use the clippings for mulch. Which leads me to olpeaÂs comment; yes most industrial grade agents contain some heavy metals and possible PBBÂect. Just how many PPM would depend on the manufacture, and with most industrial liquids made in China or Mexico where product safety is the last thing on their mindsÂÂah I would just pick up some sulfur as opposed to sending battery acid out for lab analysis.

I mean hey, I am feeding this stuff to my kids and eating it myself....so cost plays second fiddle, to safety IMHO.

    Bookmark   May 10, 2010 at 6:42PM
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