# Paphiopedilum compost and calcium tolerance



## Bjorn (Apr 12, 2013)

When composing a proper compost, one often faces the question, addition of limestone or not? Although many paphiopedlums grow on or adjacent to limestone itis claimed by some authors that the never grow on the rock itself, merely in the moss and debris covering the moss. Well, to be brief, during the last couple of years, I have used a compost mix that is composed of more or less entirely of marble chips supplemented with coarse dolomite and a little sand and bark. The results can be seen in these thread:
http://www.slippertalk.com/forum/showthread.php?t=28212
Recently I have reconsidered the opinion about marblebeing more or less inert, it does i crease pH rather quickly I have noticed in tests with water plus a grain or two of marble, minutes. Also doing potting of some of those composts, I have found a big difference i. Root growth. So, depending on whether the roots grow into this limestone gravel mix, the following has been seen:
1)paphiopedilum whose roots do not mind limestone gravel:
Malipoense
Micranthum eburneum
Tranlieanum
Vietnamense
Helenae album
Stonei
Armeniacum
Emersonii(?)
Hangianum(?)
2) uncertain status based on observations roots in limestone mix
Topperii
Charlesworthii
Esquirolei
3) those that do not grow roots in limestone mix
Rothshildianum
Jackii(???)
Anitum
Randsii

Well these are based on my observations on seedlings. Seems as if parvis are quite tolerant, the others are more questionable. Based on these observations I have decided to use more bark based mixes, my favourite has for many years been the pretty good mix of Lance Birk; 8parts bark, 2parts sheet moss and 1part sand.


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## ALToronto (Apr 12, 2013)

You should add Delenatii to category 3. 

Marble is a type of limestone. It's metamorphic rather than sedimentary, but chemically, they're very similar. Generally, anything that is etched by acids is alkaline in nature and will increase the pH of water. If in doubt, pour some vinegar over the material and see if it foams up and fizzes.


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## Stone (Apr 12, 2013)

Bjorn, My belief is that you should totally disregard the use limestone, marble, oystershells, coral etc. in the belief that the plants will ''grow better'' with these materials included in the mix. The inclusion will probably not do too much harm if there are enough acid forming components or fertilizer keep the pH below 7. The very fact that many of these ''limestone'' species can be found in trees or thick moss completely apart from the stone tells me that they will do perfectly well without it. One case is Cattleya walkeriana. It grows both on bare limestone rocks as well as trees, but mainly on the rocks. They ''choose'' the rocks more often not because of the chemistry of the rock but because there is more available water from condensation runoff and seepage and it is more easy to establish themselves there. I think its the same for the paphs etc. If you look at some of the habitat pictures of paphs you will often see other orchids growing next to them like dendrobiums, coelogynes etc. but you will also find these same plants on the trees becuse they have pseudobulbs and can handle drying out more than the paphs. The difference is in moisture availability nothing more. Nothing to do with the pH or the Calcium bicarbonate.
Have a look at this post from a couple of years back:
http://www.slippertalk.com/forum/showthread.php?t=23023
I believe these materials are best used in a finely ground form to adust pH if it becomes too acid. IMHO!


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## gonewild (Apr 12, 2013)

Small Phrag kovachii seedlings grow better with limestone material added to the surface as opposed to only receiving Ca from the fertilizer. When the limestone is mixed in the media they grow even better by about 50%. For this species the roots benefit from limestone contact.


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## SlipperKing (Apr 12, 2013)

I know I was unable to grow esquirolei until I added limestone rocks to the bottom of the pot. The roots do attach but these rocks are probably on releasing the same chemistry as your marble. With straight orchid mix I always rotted off the roots.


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## Stone (Apr 12, 2013)

gonewild said:


> Small Phrag kovachii seedlings grow better with limestone material added to the surface as opposed to only receiving Ca from the fertilizer. When the limestone is mixed in the media they grow even better by about 50%. For this species the roots benefit from limestone contact.



It may be the Ca from the fertilizer is not readily available but I doubt it. If what you say is true then its the only plant in the world that behaves like this.
I've grown Ariocarpus species which grow on pure clean limestone in Texas. If you try that in a pot they will die. They need an acid mix to grow well. So Lance I think you should go back and find out why they do better with limestone. It doesn't have magical powers that I know of. It can only do 2 things: supply Ca. and raise ph (very slightly if courser than a couple of mm) You can do both without itoke:


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## Stone (Apr 12, 2013)

SlipperKing said:


> I know I was unable to grow esquirolei until I added limestone rocks to the bottom of the pot. The roots do attach but these rocks are probably on releasing the same chemistry as your marble. With straight orchid mix I always rotted off the roots.



So why can others grow it well without limestone at the bottom of the pots? Something else was going on. Probably an imbalance between Ca. Mg. and dare I say K...........


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## gonewild (Apr 12, 2013)

Stone said:


> It may be the Ca from the fertilizer is not readily available but I doubt it. If what you say is true then its the only plant in the world that behaves like this.
> I've grown Ariocarpus species which grow on pure clean limestone in Texas. If you try that in a pot they will die. They need an acid mix to grow well. So Lance I think you should go back and find out why they do better with limestone. It doesn't have magical powers that I know of. It can only do 2 things: supply Ca. and raise ph (very slightly if courser than a couple of mm) You can do both without itoke:



I have no science explanation of the results but I did a thorough trial to discover the result, it is not a casual observation. The fertilizer I used had available Ca so that was not the issue. I ran the trial with various fertilizer combos and the result was consistent. I discussed this with Alfredo Manrique in Lima and he tried the mix and reported improved growth also. The fact is the plants benefit when their roots contact limestone. It is not a matter of pH or Ca availability there is some reason the roots need limestone contact. Perhaps there is an ionic reaction between the stone and root tissue. There is a lot more to how plants function than we know. Maybe touching limestone is a comfort and keeps them from being home sick? oke:


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## Bjorn (Apr 13, 2013)

Stone said:


> Bjorn, My belief is that you should totally disregard the use limestone, marble, oystershells, coral etc. in the belief that the plants will ''grow better'' with these materials included in the mix. The inclusion will probably not do too much harm if there are enough acid forming components or fertilizer keep the pH below 7. The very fact that many of these ''limestone'' species can be found in trees or thick moss completely apart from the stone tells me that they will do perfectly well without it.
> 
> I believe these materials are best used in a finely ground form to adust pH if it becomes too acid. IMHO!



The use of marble chips is partly because its convenient to use, not so much due to the pH increasing properties. The latter is actually happening rather quickly even with small amounts of "rocky" pieces of marble. No need to mill etc. I think that it is fair to imagine that the water film on such aggregates have a rather high pH, perhaps touching 8 and is rich in calcium ions from the neutralisation of the acid fertiliser mix. But not much, i add some 100-200ppm fertiliser to all my water. Back to the water film, its in other words enriched in calcium. As long as the root tips do not brown or stop by touching the marble, I would say the plants I list as marble liking are tolerant and perhaps even like the limestone if they cling to it. Dont you agree? Your fellow australian, the late J . R. Rentoul wrote a series of books on orchid growing in the nineteen seventies or eighties. You might have heard about them? In one of thosehe advocates the use of builders lime, matured for a year or so as supplementation. Also slag from coal he though excellent. Excellent books but hardly available nowadays. Back to the marble topic. My experience with using marble, have shown some astonishing results on some species, like for vietnamense. At my place in my mix they grow like weed. And so do micranthum. eburneum. Rothschildianum does not like the marble. So what is the reason for that? IMHO it has to do with seepage. Many of the species thay I list as limestone tolerant are growing in places on limestone where they are exposed to seepage water. This seepage water has been in contact with the limestone and become higher inpH and richer in dissolvable nutrients from the rock. Remember that the rainwater normally is slightly acid. Whay happens is that the acid rainwater dissolves trace minerals and calcium the pH raises to perhaps 7or7.5 and the balance of the elements in that water gets wery much skewed towards calcium. The seepage water tricles down the rock, wets the moss, and there you are, plants growing in the moss not touching the limestone but enjoying the chemical conditions of the limestone.
Does this make sense? Is it possible to follow me?
Last but not least, I am talking about tolerance, and perhaps even preferance of limestone, not the necessity of it as long as calcium etc is supplied though the water.


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## Bjorn (Apr 13, 2013)

gonewild said:


> Small Phrag kovachii seedlings grow better with limestone material added to the surface as opposed to only receiving Ca from the fertilizer. When the limestone is mixed in the media they grow even better by about 50%. For this species the roots benefit from limestone contact.



Kovachii and most of its hybrids are other plants that seem to enjoy marble chips. I grow them in almost entirely marble, and their roots always enjoyed it. The growth did not really take off though before I supplemented nutrition with urea. Might have been a coincidence, the plants had time to adjust plus the addidtion of urea also implied an increase in potassium as well. The latter isno good latin in this forum, I know, and perhaps not necessary.oke:


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## Bjorn (Apr 13, 2013)

Stone said:


> It can only do 2 things: supply Ca. and raise ph (very slightly if courser than a couple of mm) You can do both without itoke:



it can do more than that, if it is a natural rock, then it may release trace elements, and also it may remove toxic elements from the solution alternatively store nutrition. If calcium phosphate is formed, it may later suppy the plant with phosphorous. Just suggesting alternativesoke:


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## Stone (Apr 13, 2013)

Bjorn said:


> QUOTE] I would say the plants I list as marble liking are tolerant and perhaps even like the limestone if they cling to it. Dont you agree?


 Its possible but I don't think you can assume that they cling to the limestone because they need or enjoy the lime because they also cling very well to polystyrene which contributes nothing towards nutrition I think. But you may be right although I see no reason why they would prefer contact with the stone compared to a similar chemistry in the soil water surrounding the roots in a bark media.


> Your fellow australian, the late J . R. Rentoul wrote a series of books on orchid growing in the nineteen seventies or eighties. You might have heard about them? In one of thosehe advocates the use of builders lime, matured for a year or so as supplementation.


Yes I have all his books and I have read them many times. When that point about the mortar was written, I believe many growers were having difficulty growing brachypetalum and found improvement with the mortar addition. In those days most paphs were grown in tan bark ( a by-product from the leather tanning industry) or other plain bark and oak leaves etc. Maybe the addition of the mortar was enough to supply the extra bit of Ca or pH which these species may need? Or perhaps it reduced the water holding capacity of the bark. These days all the good bark for orchids is pre-treated with Dolomite and it is no longer necessary to add the pieces of concrete to get the same results. However long term management may be easier with the stone peices and less decomposing materials. I think it may have more to do with the nature of the substrate tha the chemistry. Many of these plants like vietnamense and brachys and even hangianum and emersonii seem to grow in a kind of decomposed soil/humus material not so much leaf mold. A friend of mine who saw godefroyae in the habitat told me they grew in a hard red dirt in the limestone cracks. this is a very stable type of material with not too much organic decomposition going on. Maybe the limestone also help to duplicate this?? The point I'm trying to make is that if the chemistry is right it should be possible to grow these plants to very high standards in straight rock wool ( which has been done in France I believe) or Leca which has been done in Canada. But if you get good results from the marble chips you should definitly continue to use it.


> Many of the species thay I list as limestone tolerant are growing in places on limestone where they are exposed to seepage water. This seepage water has been in contact with the limestone and become higher inpH and richer in dissolvable nutrients from the rock. Remember that the rainwater normally is slightly acid. Whay happens is that the acid rainwater dissolves trace minerals and calcium the pH raises to perhaps 7or7.5 and the balance of the elements in that water gets wery much skewed towards calcium. The seepage water tricles down the rock, wets the moss, and there you are, plants growing in the moss not touching the limestone but enjoying the chemical conditions of the limestone.
> Does this make sense? Is it possible to follow me?


Yes! I agree that is most likely exactly what is going on but in my opinion it is the water availability from the seepage that is the real reason that they are there in the first place. But picture this--- You go to the habitat and build a cliff of sandstone next the limestone with the same cracks and the same seepage and the same exposure and aspect etc etc, and you left it for a few decades. Would you not find all the same species colonizing the sandstone or would it be bare? Remember that the paphs grow with grasses and ferns and mosses and many other plants which have all evolved with the same soil chemistry. Would they all avoid the acid sandstone cliff? I think it would be just another surface on which to grow.


> Last but not least, I am talking about tolerance, and perhaps even preferance of limestone, not the necessity of it as long as calcium etc is supplied though the water.[/


Yes but how do you tell the difference? I really love the way Dr. Tanaka grows his brachys. They are some of the best, biggest, cleanest plants I have seen and he does not use limestone. But he does use baked clay and stones ect so he can just let them grow without disturbing them for may years. Have you needed to repot you vietnamense in the chips? If the roots were in a very good condition, could you simply transfer to a bigger pot without touching the roots?


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## Bjorn (Apr 13, 2013)

Mike, 
Many good points you have and I agree to most of it. The reason for posting this thread was merely as a kindof notebook, not so much claiming the absolute need for limestone, but more like; if you want to, good results have been obtained for these species in limestone. And also for these(the last group) species you should not use limestone, at least not to a large extent. 
You are not right supposing that most bark is treated with dolomite, in Norway where I live its even difficult to get good quality raw bark, screened is luxury and orchiata is non existent. So we have to do the best out of whatever we get. 
I am thrilled to find another one having the books of Rentoul. I have them all as well. Perhaps my favourite books although not so straight forward always. You simply have to read, which seems difficult for many people nowadays.
It may interest you that after a year or so with k-lite, i decided to modify the recipe with urea and a bit more potassium plus the micros at a slightly higher level. The result after some months at approx 200ppm is much greener leaves and good growth. This was prior to my silicon fertilisation, which seem to impart less ifections by erwinia and phytophora.
Bjorn


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## Stone (Apr 13, 2013)

I wish my vietnamense plants grew like weeds! For this reason alone I would try the limestone or marble chips just as an experiment but they are difficult to find here. Most of Australia is sandstone. Maybe I could find a marble table and smash it up:evil: Do you know the composition of your marble? Does it come from dolomite as in Italy? In other words, how much Mg is in it?


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## Rick (Apr 13, 2013)

I would consider that more than one pathway of interaction is going on, and in general once you start working with soluble ppms of greater than 50 for just about anything element you are outside the realm of ecological relevance for orchids, and are now working on toxicity experiments. 

pH is not influenced by calcium but by carbonates/bicarbonates. I doubt you would get the same results by adding calcium sulfate or calcium chloride since those forms of calcium do not supply significant buffer to counter the organic acids in bark/moss/CHC. So its not really proper to consider "Ca tolerance" when you are discussing lime application with the express purpose to change pH (alkalinity). 

The uptake and utilization of N is based on pH (alkalinity), and the form of N available (not dependent on Ca concentration).

There are competitive interactions between the primary cations (Ca/Mg/K/Na) that are not directly related to pH.

Phosphorus availability is also effected by calcium availability and pH together.

Pot pH (alkalinity) can change very quickly and seems to be one of the least controllable factors we deal with. Especially when we use high doses of various salts, the pot conditions seem to seesaw all over the place or incur high salt levels. It's like trying to paint a picture by splashing on gallons of paint and then scraping 99% of it off to get what we want. Blaming this on specific tolerances to various elements for the various species has not seemed to pan out for me.


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## Rick (Apr 13, 2013)

You mentioned roth as being Ca intolerant, and as a plant from serpentine geology that could make sense. Serpentine is heavy in alkaline magnesium silicates, and doesn't have lots of Ca (compared to your average soil condition).

But the pH is generally higher. So why are the roths effected negatively by high pH?

Interestingly on a paper I found on leaf tissue concentration of plants over serpentine geology, showed a normal ratio of NPK Ca/Mg. There was more Ca than Mg despite the elevated levels of Mg in the serpentine soil.

So is roth sensitive to high Ca or low Mg? How specific is the nitrate reductase system to pH AND TDS conditions (both effect the plants ability to use nitrate and this seems to be a species specific adaptation). Urea benefits could be demonstrating that the pH and TDS is out of range with optimal nitrate use. All that CaCO3 could be hoarding all the P so rather than seeing calcium toxicity, are you seeing phosphorus starvation (or are the two concepts synonymous:evil


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## Rick (Apr 13, 2013)

gonewild said:


> Small Phrag kovachii seedlings grow better with limestone material added to the surface as opposed to only receiving Ca from the fertilizer.



What kind of fert with what kind of irrigation water? What was total amount of Ca? Was it less than the amount of K going into the system?

What did pot pH do with and without the limestone?

I'd like to work with more than just my single plant, but seems like folks were loosing PK's right and left regardless of whether or not they limed the pots. I do have limestone gravel in the basket with mine, but with low K, it doesn't have to fight an uphill battle to keep its Ca content up.


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## gonewild (Apr 13, 2013)

Rick said:


> What kind of fert with what kind of irrigation water?


RO water.
MSU fertilizer
Calcium Nitrate
Magnesium Sulfate
Nutrients in several different combos including Only with CaNO3.
In all cases limestone mixed in had a positive effect.



> What was total amount of Ca?



I don't remember specific Ca offhand but I generally ran the total ppms at about 400-500


> Was it less than the amount of K going into the system?


Only when it was limited to the CaNO3+MgSO4 and then there was no K added.
My focus was on mixing in the limestone as compared to surface only not the nutrient ratios.


> What did pot pH do with and without the limestone?



Again I don't remember without going back to my old notes. But the pH did not change much whether the limestone was mixed in or surface applied. But that is measuring pH of the water flow not the media.



> I'd like to work with more than just my single plant,


sending you a pm



> but seems like folks were loosing PK's right and left regardless of whether or not they limed the pots.



I did not loose any plants that were planted out of 4 flasks. :drool:



> I do have limestone gravel in the basket with mine, but with low K, it doesn't have to fight an uphill battle to keep its Ca content up.



Low K may negate the mixed in limestone but I still think it will have a positive effect beyond pH.


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## Bjorn (Apr 14, 2013)

Stone said:


> I wish my vietnamense plants grew like weeds! For this reason alone I would try the limestone or marble chips just as an experiment but they are difficult to find here. Most of Australia is sandstone. Maybe I could find a marble table and smash it up:evil: Do you know the composition of your marble? Does it come from dolomite as in Italy? In other words, how much Mg is in it?


Well, I still have to flower any. But the plants really grow well. And they are pottet in a marble, sand, bark mix with a little crystalline dolomite as well. I do not have analyses of anything except the dolomite, that is quite pure stoichometric doublecarbonate. From the looks, the marble seems to be the table kind of marble. Should be relatively inert except to acid. Acid water with a few grains quickly changes pH towards 7or even higher. As with the dolomite that is coarse crystalline, looks a bit like coarse sugar. Might of course be that the good growth of the vietnamense comes from other factors, like environmental. I have cool nigths still down to 6-7degrees at nigth. However when they were in compots they enjoed some 16degrees at night and still grew...I do not knowwhat itcould be except the compost. Btw the marble is intended to be used for decorative purposes in gardening.



Rick said:


> I would consider that more than one pathway of interaction is going on, and in general once you start working with soluble ppms of greater than 50 for just about anything element you are outside the realm of ecological relevance for orchids, and are now working on toxicity experiments.


I guess this is a general statement not connected to this particular topic? If not, then Please elaborate a bit on the relevance.


Rick said:


> pH is not influenced by calcium but by carbonates/bicarbonates. I doubt you would get the same results by adding calcium sulfate or calcium chloride since those forms of calcium do not supply significant buffer to counter the organic acids in bark/moss/CHC. So its not really proper to consider "Ca tolerance" when you are discussing lime application with the express purpose to change pH (alkalinity).


ok, so pH is not influenced by anything but the carbonate/hygencarbonate(aka bicarbonate) equillibria? Sounds strange, in my perception its the dissolved Calcium that is most governed by that one. I guess that what you intend to say is that in normal water its the alikalinity that gives the pH. I think you have misunderstood my post a bit, Iwas not claiming Ca tolerance as such, its tolerance to having loads of limestone in the mix. For some species it does not matter, for others its detrimental to root growth, as the mix mostly consist of carbonates, without much bark and moss, it seemed irrelevant to discuss changes that would appear to the moss. I do agree that it would not give the same result to use calcium sulphate or for that sake chloride as aggregates. 


Rick said:


> The uptake and utilization of N is based on pH (alkalinity), and the form of N available (not dependent on Ca concentration).
> 
> There are competitive interactions between the primary cations (Ca/Mg/K/Na) that are not directly related to pH.
> 
> Phosphorus availability is also effected by calcium availability and pH together.


These things can be disputed but agree that primarily its the pH that is relevant here. But, you do agree that liquid in contact with marble would not stay acid for long?


Rick said:


> Pot pH (alkalinity) can change very quickly and seems to be one of the least controllable factors we deal with. Especially when we use high doses of various salts, the pot conditions seem to seesaw all over the place or incur high salt levels. It's like trying to paint a picture by splashing on gallons of paint and then scraping 99% of it off to get what we want. Blaming this on specific tolerances to various elements for the various species has not seemed to pan out for me.


I do agree that most of the fertiliser we pour on our plants are spoilt. I cannot agree that I use high amounts though, generally I have been using some 100-200ppm TDS equivalent to 18-36ppm N. But agree, perhaps 99.9% does not get used.


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## Bjorn (Apr 14, 2013)

Rick said:


> You mentioned roth as being Ca intolerant, and as a plant from serpentine geology that could make sense. Serpentine is heavy in alkaline magnesium silicates, and doesn't have lots of Ca (compared to your average soil condition).
> 
> But the pH is generally higher. So why are the roths effected negatively by high pH?


They are not Ca intolerant, they do not like loads of marble in the compost. I have no reason to claim anything else.btw i have tried with addition of olivine that is a basic magnesiumsilicate, but could not see any difference.


Rick said:


> Interestingly on a paper I found on leaf tissue concentration of plants over serpentine geology, showed a normal ratio of NPK Ca/Mg. There was more Ca than Mg despite the elevated levels of Mg in the serpentine soil.
> 
> So is roth sensitive to high Ca or low Mg? How specific is the nitrate reductase system to pH AND TDS conditions (both effect the plants ability to use nitrate and this seems to be a species specific adaptation). Urea benefits could be demonstrating that the pH and TDS is out of range with optimal nitrate use. All that CaCO3 could be hoarding all the P so rather than seeing calcium toxicity, are you seeing phosphorus starvation (or are the two concepts synonymous:evil


Guess the explanation is that roth grow in humus and detrius on top of the serpentine without much interaction. Since thee is no dry season where it lives, it is not dependent on seepage water and has had no reason to adopt to the implication of that, like higher pH, dissolved salts etc. 
The benefits of urea is according to my perception that plants prefer ammonia, NH3, for absorption. To deal with NO3-, nitrate they have to reduce it to ammonia, this produces alkalinity. On the other hand, For the plant to use ammonium, they expel a proton, H +. This is acidifying the soil. And is probably true for ammonium fertilisers. What people tend to forget when urea is used is that urea splits into NH3 by an enzymatic process and this can be absorbed directly without production of protons. As a matter of fact, I have noticed that if urea containing water at 50ppm or so urea is left for a day or two, the pH increases from5.5 to beyond 7 while the conductivity increases. This is probably due to the production of ammonium from ammonia that comes from the enzymatic decomposition of the urea.


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## Rick (Apr 14, 2013)

Bjorn said:


> but agree that primarily its the pH that is relevant here. But, you do agree that liquid in contact with marble would not stay acid for long?



Totally agree, that is the point of that little test I did with the aragonite in moss.

Seems like most of the debate may be caused by mixup in terminology. Or maybe you are thinking with a Norwegian accent and I am loosing track in my English

When you said that you saw no difference in using olivine instead of marble does that mean you (A) saw no positive improvement with olivine, or (B) or olivine was just as good as marble? (BTW olivine looks pretty much looks like the "serpentine rock").

If your answer is B, then pH/alkalinity for pot environment is indeed the parameter we are looking at.

I did see a comment in a previous post that said that seepages impacted by limestone are "nutrient rich". I can attest from testing well waters and seepages in limestone areas that they are virtually devoid of N and K. Some local systems have elevated P (maybe a few ppm at most). The bulk of the TDS is some mix of calcium and magnesium with varying amounts of sulfate, chloride, and bicarbonate. Also as you predicted with the roth example, the amount of TDS is highly variable depending on rainfall, contact time, and variations on the crystal hardness of the rock. Many seeps have very short contact times coming from shallow perched aquifers. Those waters generally have very low TDS compared to deep water wells pumped from under the same geology.


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## Rick (Apr 14, 2013)

A useful cautionary with regards to negative interactions from excess Ca (besides the possibility of phosphate insolubility) is suppression of magnesium uptake at very high Ca.

For that reason I would prefer dolomite instead of aragonite (closer to 50/50 Ca/Mg), or supplement more Epsom salt in irrigation water if using a high % calcium buffer.

But overall I keep opening up the mix and pot (basket), and water more with more dilute solutions to see better results. This follows the roth example that you just discussed, that high rainfall over humus systems negates exposure to high TDS/pH.


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## ALToronto (Apr 14, 2013)

Very interesting discussion. Just for giggles, how would all these results translate to a chemically inert, inorganic medium? I'm thinking lava rock and LECAs, both chemically similar. Do we need an organic medium, given all its problems in a closed, self-contained environment? Have people had success growing this way (and I'm not talking semi-hydro)?


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## gonewild (Apr 14, 2013)

Stone said:


> Its possible but I don't think you can assume that they cling to the limestone because they need or enjoy the lime because they also cling very well to polystyrene which contributes nothing towards nutrition I think.



Not trying to argue but.... polystyrene is not inert. It dissolves in water and releases chemicals. No one actually knows how it affects plant growth. It also has strong ionic charges. 

And now get this part..... Polystyrene products are formed to shape in molds. The molds are sprayed with release agents which also coat the surface of the polystyrene products.......Calcium Stearate is used as a release agent. 
So the polystyrene that the roots attach may be covered with Calcium.


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## Bjorn (Apr 14, 2013)

Rick said:


> Totally agree, that is the point of that little test I did with the aragonite in moss.
> 
> Seems like most of the debate may be caused by mixup in terminology. Or maybe you are thinking with a Norwegian accent and I am loosing track in my English


Guess you are touching it, different languages and mindsets. Mix that with terminology and there you are.


Rick said:


> When you said that you saw no difference in using olivine instead of marble does that mean you (A) saw no positive improvement with olivine, or (B) or olivine was just as good as marble? (BTW olivine looks pretty much looks like the "serpentine rock").
> 
> If your answer is B, then pH/alkalinity for pot environment is indeed the parameter we are looking at.


The main reason for adding olivine was to check whether it could have some influence being an ultrabasic mineral closely resembling serpentine. While serpentine was unavailable, olivine was in my posession so... But the answer is not straight forward; the olivine was added to the marble mix without showing any significant differences to those without olivine. So its difficult to say anything except that the olivine does not contain any magic ingredient.


Rick said:


> I did see a comment in a previous post that said that seepages impacted by limestone are "nutrient rich". I can attest from testing well waters and seepages in limestone areas that they are virtually devoid of N and K. Some local systems have elevated P (maybe a few ppm at most). The bulk of the TDS is some mix of calcium and magnesium with varying amounts of sulfate, chloride, and bicarbonate. Also as you predicted with the roth example, the amount of TDS is highly variable depending on rainfall, contact time, and variations on the crystal hardness of the rock. Many seeps have very short contact times coming from shallow perched aquifers. Those waters generally have very low TDS compared to deep water wells pumped from under the same geology.


if I said nutrient rich, then I meant richer in some nutrients that the limestone could carry. Typical would be some trace elements. Roth mentioned years ago that hangianum (or was it vietnamese?) was found on limestone near lead mines in northern vietnam. Things like that could be released by the dissolution of limestone by acid. Of courselimestone could act as a stabilising buffer fo phosphorus as well


Rick said:


> A useful cautionary with regards to negative interactions from excess Ca (besides the possibility of phosphate insolubility) is suppression of magnesium uptake at very high Ca.
> 
> For that reason I would prefer dolomite instead of aragonite (closer to 50/50 Ca/Mg), or supplement more Epsom salt in irrigation water if using a high % calcium buffer.
> 
> But overall I keep opening up the mix and pot (basket), and water more with more dilute solutions to see better results. This follows the roth example that you just discussed, that high rainfall over humus systems negates exposure to high TDS/pH.


Guess that we could differentiate between those experiencing a dry season relying on seepage water from limestone, and those that gets rain all year (all except those from the monsoon areas?) I do expect that typical limestone-cliff dwellers like sanderianum and stonei also tolerates limestone well although they are not exposed to dry seasons. At least I have indications that they do.


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