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Decomposed granite and soil pH?

Posted by robinpla 10b (My Page) on
Thu, Jan 31, 13 at 0:03

Lately I have been sieving decomposed granite to use as a topsoil to my succulent plants. A few days ago I read somewhere that decomposed granite can be used to lower the pH of the soil. Have I made a huge mistake to use it as a topsoil? Will this potentially stunt and possibly kill plants?


Follow-Up Postings:

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RE: Decomposed granite and soil pH?

Maybe decomposed granite is different from place to place. I do know that the decomposed granite soil of the Llano Uplift of Central Texas to the west of me is considered alkaline soil. It probably is not as alkaline as my alkaline lime based caliche wich is strongly alkaline, but it is not used to lower soil PH. It might make it a bit more neutral if your soil is very high. I like to add it because of its trace minerals and it comes with a bit of iron rich clay in it also. the granite is Texas Pink.


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RE: Decomposed granite and soil pH?

  • Posted by nil13 z21 Mt. Washington L (My Page) on
    Thu, Jan 31, 13 at 11:10

The soil tests I have received from DG soils around Los Angeles have all shown pH around 7.3-4.


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RE: Decomposed granite and soil pH?

Would you recommend getting a soil pH test kit? I have no clue where my DG comes from, and even if I did I wouldn't know the pH.

What's the recommended pH range for most succulents? I know my adenia glauca loves acid soil and I think I have another plant that prefers alkaline soil. But in general if I don't know the plant's preference should I aim for neutral 7 pH?


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RE: Decomposed granite and soil pH?

Its a relative thing, that pH. If I take my neutral pH compost and mix it with alkaline soil, it will lower the pH of the soil. If I take that very same neutral compost and mix it with an acid soil it will raise the pH. Ultimately, it cannot bring acid soil higher than neutral, nor bring the alkaline soil lower than neutral as that is its own pH. As for granite dust, it is much less soluble than, say my compost or even limestone, so even if it is acidic, the relative effect is close to neutral.

tj

This post was edited by tsugajunkie on Thu, Jan 31, 13 at 20:19


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RE: Decomposed granite and soil pH?

  • Posted by nil13 z21 Mt. Washington L (My Page) on
    Thu, Jan 31, 13 at 20:31

You're sieving purchased DG? I've done that. It's a PITA! Just go buy a bag of pumice. lol.


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RE: Decomposed granite and soil pH?

I plant most of my plants in 3/4 pumice and 1/4 commercial cactus mix (not all commercial mixes are the same, I have my favorite:), then top it off with some nice top dressing. But it's really hard to find top dressing outside of the C&S club sales. A 60 pound bag of DG is $5, which is basically free compared to the commercial stuff. Pumice doesn't look too great as a top dressing :)


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RE: Decomposed granite and soil pH?

  • Posted by nil13 z21 Mt. Washington L (My Page) on
    Fri, Feb 1, 13 at 11:27

ahh, it's for topdressing. The topsoil bit confused be a bit. I get bags of gravel from a really good stone yard for about $12/75# bag with no sifting required. But then I have also sifted shale from landslides in the neighborhood in order to get a nice local gravel mulch for the garden, so I really shouldn't talk, lol.


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RE: Decomposed granite and soil pH?

I like crushed rose granite for top covering. It is cheap where I live. But it makes some of my larger pots heavy and tip them beyond the picking up comfortably and carrying in for cold front dilemma, AAAARGH.


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RE: Decomposed granite and soil pH?

No one said beauty came for free ;)


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