# Oyster Shell Question



## Kawarthapine (Mar 1, 2015)

Instead of buying Paph Magic (a great product) I decided to make my own blend.

I bought a 15kg bag of crushed oyster shell (Coastal Blend) for $35. Cdn that should last me the rest of my life! I bought from a local Agricultural store (TSC) that sells the additive for poultry.

I heard I should first wash the crushed shell then bake it to remove containaments and to sterilize.

Can folks comment/advise me on baking temp and time?

Lastly, I was going to add some silica sand to the blend. 

Thoughts, suggestions would be appreciated.

Many thanks!


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## gonewild (Mar 1, 2015)

I have always rinsed the oyster shell, just to remove the dust. There probably is no reason to remove the dust in reality.
But I have never baked it or attempted to sterilize it in any way.
I don't think there is any reason to sterilize it unless you also sterilize every component you use in your mix.

I also usually throw in a little sand just because.


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## Rick (Mar 1, 2015)

I quit using calcareous, and pH adjusting additives a couple years ago, and just cut back N application to a fraction of what I used to add.

There's plenty of Ca and bicarbonate in even soft tap water to support the plants (even for "limestone" dwellers) without adding things to the potting mix.

I started an experiment with a Paph lowii back in November 2014, with continuous water at the roots in a support matrix of glass beads. (Kind of like those decorative bamboo things they sell at Trader Joes). It's growing just fine to date. Adding roots and leaves.


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## Kawarthapine (Mar 1, 2015)

I appreciate the feedback.

I am going to do a comparison test using paphs and phrags.

For a year I am going to compare (1) controls (do nothing); to (2) a paph medium with addition of sands and shell; and (3) phrags potted in Leca clay without shells with (4) those with addition of shells. If I have enough divisions I may expand trial to include one group of plants with MSU and another group with K-Lite.

You may be right about the shell having a very minimal to non-existent benefit but the fun is in the experiment and frankly, I think my plants like the attention...

...or as my better half has suggested, I'm simple nuts for orchids.


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## Ozpaph (Mar 1, 2015)

I use it. Im always wary of the possibility of salt contamination, so buy the expensive aquarium stuff. No idea if its better.
I dont sterilize or wash.


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## Rick (Mar 1, 2015)

Kawarthapine said:


> You may be right about the shell having a very minimal to non-existent benefit but the fun is in the experiment and frankly, I think my plants like the attention...



I didn't mean to imply that oyster shell has no effect. It's very effective at buffering soil pH, and the material has been used in agriculture for that reason for decades (maybe centuries). So you don't have a novel experiment going, but you are welcome to develop your own experiences. 

I used it myself when I started with orchids in 2001. However, what I learned (after sending a lot of orchids to that great compost heap in the sky) is that all I was doing was counteracting excesses from the other end. Essentially "sweeping the @$#@& under the carpet." All that attention that I was lavishing on my plants was actually detrimental, and I now get much better results with a lot less material and effort.


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## Ray (Mar 2, 2015)

I don't know about your oyster shell, but in order to make it clean enough to not stink up the world, the oyster shell I've seen here for poultry use is calcined (fired at very high temperatures) to eliminate organic matter.


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## dodidoki (Mar 2, 2015)

You have better not bake it. Reason is next: Ca (CO3)2 gets in two parts by heat: CaO and CO2. CaO+H2O= Ca(OH)2, it is very alcalic and very bad for roots. If you yould like to desinfect is better to boil it in a preassure cooker.


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## dodidoki (Mar 2, 2015)

It is duobtful that there is any positive effect of oyster or not. Rain water always contains few of solubile CO2 ( HCO3), that is why the rainwater is slightly acidic ( 6,2-6,5) and can solve a little Ca and Mg from lime-stone. But if you water your plant with pure , stagnant rain water, this effect of water won't work well.


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## gonewild (Mar 2, 2015)

dodidoki said:


> It is duobtful that there is any positive effect of oyster or not. Rain water always contains few of solubile CO2 ( HCO3), that is why the rainwater is slightly acidic ( 6,2-6,5) and can solve a little Ca and Mg from lime-stone. But if you water your plant with pure , stagnant rain water, this effect of water won't work well.



With that in mind the oyster shell does provide some Ca whenever you apply acidic fertilizer, regardless of the source water supply. Also likely some form of micro organisms decompose the oyster shell to liberate Ca.


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## Rick (Mar 2, 2015)

Oyster shell absorbs phosphate and some heavy metals pretty good too. So keep in mind w/regard to low phosphate fert applications and the trace metals in your fert mixes.

Back when I was using it as a substrate for marine aquaria, it would buffer the pH at 8.3, and suck up almost as much copper as I could throw at it.

The copper was being applied to kill parasitic protozoans that can plague saltwater fish. But to get to a lethal dose you had to add about 5X more than the calculated water volume dose to saturate the absorption sites on the oyster shell.

Other calcareous substrates like aragonite, dolomitic lime, will do the same things. So you can find precedent for these materials to be used in environmental remediation projects.


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## Trithor (Mar 2, 2015)

Seems much easier to add a dose of calcium nitrate to your fertilizer regimen if the intention is to supply calcium. Our council water is very low in calcium for some reason, so I have started to add very small amounts of calcium nitrate to the water on watering days and exclude it on fertilizing days.


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## gonewild (Mar 3, 2015)

I use Calcium Nitrate as my main N source.... solves the Ca supply problem.  However I do think that some species enjoy root contact with calcareous substrate under normal non hydroponic conditions where irrigations are less frequent.


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## gonewild (Mar 3, 2015)

Rick said:


> Oyster shell absorbs phosphate and some heavy metals pretty good too. So keep in mind w/regard to low phosphate fert applications and the trace metals in your fert mixes.



Are the absorbed metals permanently bound or will they be released to plants at some point and possibly become a toxic excess?


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## Ray (Mar 3, 2015)

I think the ability of oyster shell to absorb metals, while totally factual, is irrelevant. Rick's tank substrate is hardly representative of the environments from which oysters are harvested.

Oysters themselves are wonderful filters, and if they or their shells were in an environment that allowed them to get that loaded up, we'd all get sick as hell eating them. 

I don't know if direct contact with a calcium-bearing material is necessary, but the problem I have with oyster is that you really have no idea what dose you're applying.


Ray Barkalow
firstrays.com


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## gonewild (Mar 3, 2015)

Ray said:


> I think the ability of oyster shell to absorb metals, while totally factual, is irrelevant. Rick's tank substrate is hardly representative of the environments from which oysters are harvested.



I was more thinking of the metals absorbed from the irrigation water supplied over time not what might be coming in with the shell.



> Oysters themselves are wonderful filters, and if they or their shells were in an environment that allowed them to get that loaded up, we'd all get sick as hell eating them.



The shells capacity to absorb chemicals is not related to the living oyster and really does not apply to the effect on plant nutrients. Most oyster shell used as ag feed is mined from ancient reefs and not from fresh crushed shells. All the shell I have ever bought on the west coast is from ancient deposits and would function based on mineral content absorbed and leached over perhaps thousands of years.



> I don't know if direct contact with a calcium-bearing material is necessary, but the problem I have with oyster is that you really have no idea what dose you're applying.



It may not be necessary but I have found it beneficial with some species. P.kovachii responded positively in my trials to the addition of limestone or oyster shell mixed into the substrate as compared to surface dressing or none at all. Increasing the CA/Mg content of the fertilizer did not provide equal results.


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## gonewild (Mar 3, 2015)

As a note on my above comments in my trials the nutrients rates were high and not at low levels like Rick is applying to his marbles.


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## Stone (Mar 5, 2015)

I read somewhere that some of the Ca in CalNitrate is converted to CalCarbonate in the medium. Anyone know?


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## gonewild (Mar 5, 2015)

Stone said:


> I read somewhere that some of the Ca in CalNitrate is converted to CalCarbonate in the medium. Anyone know?



Calcium Nitrate will form CalCarbonate in the presence of Ammonia but I'm not sure the conversion will happen at the low concentrations in the media


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## Bjorn (Mar 6, 2015)

you probably need a source of CO3 like CO2 in water probably at a bit elevated pH. Do not think its an issue for most growers though.


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## Rick (Mar 7, 2015)

gonewild said:


> Calcium Nitrate will form CalCarbonate in the presence of Ammonia but I'm not sure the conversion will happen at the low concentrations in the media



This is new on me.

Calcium carbonate as formed when free calcium ion is in a high pH solution so CO2 converts to bicarbonate and then carbonate ion. Calcium carbonate (limestone) is the solid precipitate in the process.

In a pot pH is rarely high enough for limestone formation. Typically we see the converse that the pot is an acidic system that dissolves limestone and releases CO2.

Nitrate ion is converted to N2 gas by anaerobic bacteria and will release bicarbonate ion in the process, but if the predominant pH system is low, then it just gets changed to CO2 and gasses off. 

Ammonia is converted to nitrate by aerobic nitrifying bacteria. This is a bicarbonate consuming process. 

So under typical pot conditions, you don't get limestone formation with fertilizer application.


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## gonewild (Mar 7, 2015)

The conversion could only happen under a controlled system with ammonia and CO2 gas so maybe I did not say exactly what I meant. I'm remembering a lecture I heard about how fertilizers are made (years ago).
So the correct answer is it could not happen in a pot of media with living plant roots.


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