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Compost PH above 7.0

Posted by bobvisaa 34222 (My Page) on
Sun, Dec 29, 13 at 1:20

My finished compost has a ph greater than 7, is this a problem? Should I add sulfer to bring the ph down?


Follow-Up Postings:

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RE: Compost PH above 7.0

What is the pH? That the apparent pH is greater than 7.0 means little,


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RE: Compost PH above 7.0

Do not be in a hurry to take any action that may not be needed.

Questions I have:
1) What do you use the compost for?
2) What is the pH of your soil?
3) What plants or flowers would you be planting?
4) What are the ingredients in your compost?


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RE: Compost PH above 7.0

Also, how did you determine the pH?


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RE: Compost PH above 7.0

  • Posted by ericwi Dane County WI (My Page) on
    Tue, Dec 31, 13 at 20:57

The only way to measure the pH of compost, that I can think of, would be to run some water through it and collect the drippings at the bottom. If you do this, you would have to use distilled or equivalent de-ionized water, so that you knew the water was pH = 7 to begin with.


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RE: Compost PH above 7.0

To measure pH of composted material is the same as measuring the pH of your garden soil.

-- Take a sample and proceed from there.


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RE: Compost PH above 7.0

Seysonn: I'm a bit puzzled. Did you mean the pH is measured the same way for soil and compost; or that the pH would be the same for both?

Thanks.


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RE: Compost PH above 7.0

I said the measuring technique/method should be the same not the value.


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RE: Compost PH above 7.0

Generally that's a 50-50 mix of the sample and distilled water, stir, allow to equilibrate for a few minutes, and test.

Hopefully you are using a good calibrated meter, as the inexpensive ones sold in the garden section are often dodgy.


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RE: Compost PH above 7.0

That is distilled water that was tested by your pH meter, which was calibrated for neutral (7.0) before mixing the soil in the water.
We always allowed the sample to sit, covered, for an hour before attempting a reading, although the soil testing labs most often test immediately after filling the sample with water of a known pH level.

This post was edited by kimmsr on Sat, Jan 4, 14 at 7:06


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RE: Compost PH above 7.0

Distilled water may not actually have a pH of 7, but it's OK because it has virtually no buffering capacity so it takes almost nothing to change it. It's not really necessary or relevant to test the pH of distilled water, and you couldn't calibrate a pH meter with it because of the instability. As long as it's distilled, the soil will bring it to the proper soil pH.

I would want to calibrate the meter at or near the expected soil pH if only a single point calibration is possible, or at two points bracketing if the meter is capable (such as 6 and 8). Also depends on what cal buffers you are able to get.


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RE: Compost PH above 7.0

I should like to thank toxcrusadr for the post on calibration above. This is useful information.


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RE: Compost PH above 7.0

Every pH meter I have looked at or used had directions about how to calibrate them and what to use for that calibration.


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RE: Compost PH above 7.0

OMG you read directions? How rare! :-] I posted with the assumption that many do not, or couldn't find them if they wanted to.


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RE: Compost PH above 7.0

Composts are now frequently becoming too salty because we have either ruined or mishandled our manures. chemical agriculture in particular is salt agriculture.


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