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soil highly alkaline potting soil

V

vovo

How do you reduce the pH of potting soil. I will grab some elemental sulphur but I've heard that takes a while to lower pH.

I made up a batch of potting soil, 1/3 perlite, 1/3 coir, 1/3 mushroom compost. I potted up a few batches and then bought a testing kit to check and the result was pH 9+.

Thoughts?
 
vovo said:
How do you reduce the pH of potting soil. I will grab some elemental sulphur but I've heard that takes a while to lower pH.

I made up a batch of potting soil, 1/3 perlite, 1/3 coir, 1/3 mushroom compost. I potted up a few batches and then bought a testing kit to check and the result was pH 9+.

Thoughts?
Click to expand...
 
Check the PH of the mushroom compost to see if it is the alkaline component. Also PH your water just in case.
 
To reduce PH, unless you are just absolutely against using it, peat moss is acidic and will bring it back down.
 
Peat seems to be very expensive here in Australia. I am using an approved kit where you add an indicator liquid to a sample of soil and then add barium sulphate which changes color which can be matched to a chart. Apparently pretty accurate but I will take a few more samples to confirm.

My understanding is that they add lime to mushroom compost which makes it basic. But to be honest I don't know.
 
interesting. never heard of that test.

the only thing you can do besides peat is aluminum sulfate.
id you do the aluminum, be careful with it, as once you overshoot... you will have to start over, or you will have to add more of the mushroom compost... throwing off your desired ratio.

you can also add some ammonium nitrogen or ammonia itself to acifify the soil slowly...
aluminum sulfate is prob. not organic though.

maby it is actually. idk. never needed it before.

it makes sense that peat is spendy there... being a marsh/bog material im sure you have no native source in austrailia.

i bet coir is cheap though, you guys are close to indonesia and some of the Polynesian island chains.

sorry that there is no organic solution to this issue... you might just have to give up the mushroom compost.
 
Since you're going into your winter you could urinate in it.  I don't recommend doing this if you're anywhere near putting plants in it but it doesn't get much more organic than using body waste ;)  The ammonia will bring the pH down and also provide nitrogen (think aquaponics)
 
a strong inorganic acid watered into the soil would actually work in the short term, but i dont think it would last very long.

aluminum sulfate works particularly well because the trivalent aluminum has a sort of buffering... ish effect on soil ph.

the reaction(hydrolysis of trivalent aluminum) is an equilibrium reaction. at low PH's its driven to the left side side and less H+ is evolved.

when the soil PH is high, it releases much more H+...

if you just dump acid into the soil what will happen is it will slowly creep back up as the soil is leached. charges of lime last years in some cases. calcium and magnesium carbonate is not very soluble, so little tiny bits of it chill inside your mix dissolving slowly and rasising ph.

you need the aluminum to balance this all out. this aluminum does not leach from soil becasue its trivalent.

it has a +3 charge soil particles love to hold on to... especially when the CEC is high and the ph is high.
 
Helvete said:
Since you're going into your winter you could urinate in it.  I don't recommend doing this if you're anywhere near putting plants in it but it doesn't get much more organic than using body waste ;)  The ammonia will bring the pH down and also provide nitrogen (think aquaponics)
Click to expand...
I am growing through winter, it only gets down to an average low of 10C/50F where I am. Might give it a tinkle anyway.

I am going to give it some elemental sulphur and in the meantime I will water in a fish fertilizer (~3.5pH) once a fortnight and maybe give it some vinegar or citric acid on alternate weeks until the sulphur kicks in.

Fingers crossed they stay healthy.
 
I have to say, 9 is a little ridiculous tbh, if you just take a little of it and drop some vinegar on it does it fizz or anything?
 
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