# Dolomite/Limestone powder



## Stone (Jun 19, 2013)

Assuming we use fertilizers without added Ca/Mg and we have very pure water, we will eventually have to apply ground Dolomite and/or Limestone to the pot. So my question is what is the general consenus as to how often to apply? I have read everything from once or twice per year to once or twice per month ( from some of Roths posts ) and everything in between.


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## Ray (Jun 19, 2013)

Personally, I'd never use powder (too much surface area for more rapid dissolution), but would stick with granular/pellets.

Of course this is coming from a guy who doesn't think top dressing is as much of a value as adding it with the fertilizer.


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## dodidoki (Jun 19, 2013)

Mike, I think it does not work. Chemically: in nature, there is some H2CO3 in rain water, it can solve few Ca and Mg from limestone. But in culture we water our plants with collected rain or RO water, there is no any H2CO3, wich can solve few Ca and Mg for plants. So my opinion that we have better to replace it with solubile Ca and Mg ions, eg. Ca(NO3)2 and MgSO4.


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## Ray (Jun 19, 2013)

dodidoki said:


> Mike, I think it does not work. Chemically: in nature, there is some H2CO3 in rain water, it can solve few Ca and Mg from limestone. But in culture we water our plants with collected rain or RO water, there is no any H2CO3, wich can solve few Ca and Mg for plants. So my opinion that we have better to replace it with solubile Ca and Mg ions, eg. Ca(NO3)2 and MgSO4.


I disagree about the carbonic acid - there is a natural equilibrium of dissolved CO2 from the air in water, producing the acid, which is why distilled or RO water shows a pH of about 5.5-5.6 after exposure to the atmoshphere.


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## eteson (Jun 19, 2013)

I have a bad experience with the Dolomite and Limestone powder... I used it as a suplement in my kovachii plants but the medium became "cemented" and some of the plants lost virtually all the radicular system.
Maybe my medium was too fine. Now I am using granular dolomite plus low K diet with best results.


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## Rick (Jun 19, 2013)

Are you adding for Ca and Mg, or pH buffer?

I think you are already adding gypsum (calcium sulfate) or epsom salts if you want to add Ca/Mg, but that won't boost your pot pH.

If you want to add to raise/buffer pot pH then lime or dolomite will do it, but for duration or amount, then just check your pour through pH. If it doesn't hit target then add more. If it drops below target after time, then reload.

The lenght of time it will last will depend on the acidity of the potting matrix, and frequency of watering/feeding. So no set answer.

I posted a quick experiment on adding the aquarium store "Cichlid Sand" product, which demonstrated it definitely buffered moss substrate, but lots of variables as described above means you "can't fly without instruments".


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## Stone (Jun 19, 2013)

Ray said:


> Personally, I'd never use powder (too much surface area for more rapid dissolution), but would stick with granular/pellets.
> 
> Of course this is coming from a guy who doesn't think top dressing is as much of a value as adding it with the fertilizer.



When I say powder I mean a ground material with particles in the 1 to 2mm size down so there is both short and long term effect. But I must admit that with very course orchid mixes, the finer material washes through pretty fast and maybe doesn't leave much left in the mix?


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## Stone (Jun 19, 2013)

Rick said:


> > Are you adding for Ca and Mg, or pH buffer?
> 
> 
> Well both I guess. As most of your off the shelf type fertilizers have high Urea/ammonium contents I must use it as a ph buffer. Most of these same feeds also have no Ca added so it will also supply that. I rather like the leaf colour and growth response with these and adding Cal nitrate every time is also a bit of a chore.
> ...


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## Stone (Jun 19, 2013)

dodidoki said:


> Mike, I think it does not work. Chemically: in nature, there is some H2CO3 in rain water, it can solve few Ca and Mg from limestone. But in culture we water our plants with collected rain or RO water, there is no any H2CO3, wich can solve few Ca and Mg for plants. So my opinion that we have better to replace it with solubile Ca and Mg ions, eg. Ca(NO3)2 and MgSO4.



I can definitly tell you that it works. Many millions of plants are raised every year using controlled release fertilizers without Ca and usually without Mg. These 2 elements are supplied via pre-plant dolomite and limestone added to the mix as well as any that may be in the water (which is the same thing) The difference is that most of these plants are sold off within 1 year and planted in the garden or whatever. But an orchid may stay in the same pot 2 to 5 years so you must replace the Ca/Mg.


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## limuhead (Jun 20, 2013)

Ok, here is a solution for you. A product called Oxyfertil Drip. A natural Calcium and Magnesium (basically Dolomite) that is specially formulated to stay in solution. Here is how I use it. I put 1/3 cup in a Gilmore 6 gallon hose end sprayer, shake it up, and spray on my hanging plants once a month. You still have to shake the hose end sprayer, but it doesn't clog...


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## Stone (Jun 20, 2013)

I can get a product called ''Liquid dolomite'' but I've never looked into it.


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## Linus_Cello (Jun 20, 2013)

What about just using crushed oyster shell?


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## Stone (Jun 20, 2013)

Linus_Cello said:


> What about just using crushed oyster shell?



Anything like that is probably ok but it needs to be fairly fine or it won't do much. Apparently anything over 1 to 2mm is quite useless. (unless you put on tons of the stuff I guess)


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## Rick (Jun 20, 2013)

That Cichlid sand is about 1-2mm, but in that test I did, 0.2 grams was able to bring the pH of a 2" pot of sphagnum moss up to 5.5 with no problem.

That's not much. At a larger doses it would push the substrate up to about 7, and TDS also went up.

If you are using bark you don't even have as much initial acid content as moss.

So I presume you could use even less to get the same effect.

The choice of nitrogen is probably a bigger driver yet. The higher percentage ammonia/urea will drive the pH down more than what moss can do by itself. 

Without fertilizing the acids in bark and moss will wash out fairly fast and the pot pH will be pretty close to the pH of your irrigation and feed water.


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## Stone (Jun 20, 2013)

Rick said:


> > That Cichlid sand is about 1-2mm, but in that test I did, 0.2 grams was able to bring the pH of a 2" pot of sphagnum moss up to 5.5 with no problem.
> 
> 
> Did you wash the sand first? Unwashed it would likely have a film of dust around the particles which would be the first to react. But what is it actually? I have a form of dolomite where a good persentage disolves as soon as you wet it where as the rest remains hard. So I guess it also depends on the make up of the material?


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## Rick (Jun 20, 2013)

Stone said:


> Rick said:
> 
> 
> > Did you wash the sand first? Unwashed it would likely have a film of dust around the particles which would be the first to react. But what is it actually? I have a form of dolomite where a good persentage disolves as soon as you wet it where as the rest remains hard. So I guess it also depends on the make up of the material?
> ...


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## cnycharles (Jun 21, 2013)

I used a bunch of the aragonite sand when I repotted last time and some things died that don't like high EC or pH; I recommend it be used very sparingly and with plants that you know can handle it, not everything without some testing to see what changes come about after adding it (the usual disclaimer to try something small-scale and see results before using for everything ;( )

There are a few flowable limestone products here in the northeast us that can be used safely by following the instructions, and I would use them before using limestone dust of unknown size and quality.they've been used enough so that there should be recommendations that you can follow safely


Sent from my iPhone using Tapatalk


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## Ozpaph (Jun 22, 2013)

I add or sprinkle Aragonite in/on the mix


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