A couple pine needle pH questions

christie_sw_mo(Z6)February 28, 2011

I'm using pine needles along with other methods to make my soil more acidic for blueberries.

Does anyone know if it makes a big difference whether the pine needles are fresh or dry?

Do some types of pine acidify the soil more than others? White Pine and Shortleaf Pine are fairly common in my area.

I would like to know if anyone has seen any detailed studies on using pine needles to lower pH and would really appreciate a link if you have one.

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Can't connect you to a link because there isn't one :-) Or one that is the slightest bit accurate, anyway.

Contrary to common belief, pine needles or other conifer needles do NOT make soil more acidic. While the needles themselves are acidic in content, once incorporated into the soil or added to compost, that acidity is neutralized by the decomposition process. If used as a mulch, you will get some slight lowering of pH at the soil surface but it is not significant. And it doesn't penetrate much below the soil surface.

If you want to lower the soil pH for blueberries, follow the traditional methods for best results - sulfur, peat moss, cottonseed meal, etc. Even compost will lower a high pH to some degree.

Here is a link that might be useful: the myth of pine needles and soil acidity

    Bookmark   February 28, 2011 at 10:13AM
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Thanks Gardengal - I've been looking on the web for specifics on Abigail Maynard's study and I'm not finding much. I did find:
"Abigail Maynard, with the Connecticut Agricultural Experiment Station at New Haven found that the pH of soil amended with 50 tons per acre of leaves for 3 years increased from 5.4 to 5.7"

I wonder if she was starting with a soil pH of 5.4 for the pine needle study also. That would be interesting to know. From what I've read this morning on different websites, I got the feeling that her study was to show that it is ok to use pine needles for mulch and that they wouldn't make the soil pH TOO low. Wish I could find more details.

Maybe there's a study out there somewhere that shows the effects of pine needles on soil with a higher pH. Couldn't that make a difference?

I found a little info about a study by Jeff Iles and Michael Dosmann showing that hardwood bark, pine bark and wood chips raised the pH of their soil over 2 years time but pine needles decreased it slightly (it didn't say how much). Their soil started with a pH of 5.9.

    Bookmark   February 28, 2011 at 11:59AM
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Let me state this again - there is NO significant relationship between applying pine needles/pine straw or any other acidic plant parts as a mulch and lowering soil pH. The leachate has virtually the same effect and pH as rainwater - about 6.0 - and will effect no substantial lowering of the soil pH. There is even less of an impact when that type of organic matter is incorporated into the soil or used as a compost ingredient. Any acidity is effectively neutralized through the process of decomposition

To put it simply, these types of material have minimal to no effect in lowering soil pH. If you need to lower soil pH, you need to look at other methods and amendments to do so.

Here is a link that might be useful: pine straw acidity testing

    Bookmark   February 28, 2011 at 1:40PM
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I enjoy these threads.

I read the quote from christie "pH of soil amended with 50 tons per acre of leaves for 3 years increased from 5.4 to 5.7" and was wondering;

a) just how significant that is, and
b) is pH rock solid stable all the time or is there a natural 'variation' based on various parameters? (precipitation, temperature, time, etc etc)



    Bookmark   February 28, 2011 at 1:50PM
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I also wonder if you realize just how much 50 tons per acre really amounts to. That's more than a ton per 1000 sq ft. I have a small lawn, but I'd be adding more than 9,000 lbs of leaves to my lawn to mimic that.

That's A LOT of leaves. And it moved the pH by .3. Note that it moved the pH up in that study, but would probably move it down for me. Generally, you'll see the addition of organic matter move the pH closer to neutral over time. But it's not a permanent change.

    Bookmark   February 28, 2011 at 4:34PM
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A soils pH (percent Hydrogen) is determined by the amount of free radical Hydrogen ions roaming around there, the more of them the lower the soils pH will measure. Organic matter is not going to significantly change those numbers, you need something that is going to pull those free ions in and lock them up. The substance that does that best is lime.
If your soils pH is too high (alkaline) then you need to loose Hydrogen ions to lower it and that most frequently involves adding sulfur, not organic matter, because sulfur will increase the number of free radicla Hydrogen ions in the soil.

    Bookmark   March 1, 2011 at 6:55AM
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