Some medium questions...

[paphioboy]

1. Can anyone please tell me the difference between karst and 'normal' limestone..? As far as I understand, karst is highly eroded and is found in coral formations washed up from the seabed. Is there a mineralogical difference if I use 'normal' limestone instead to culture paphs like brachys and parvis? People often mention that brachys and parvis often are particularly sensitive to accumulation of salts, and I was wondering if 'normal' limestone accumulates more salts than karst. By 'normal' limestone, I mean those white stones/pebbles that people use to decorate aquariums or garden pathways, which I use for my paphs.

2. Phillip Cribb, in his book 'The Genus Paphiopedilum: Vol. 2', mentions that the use of charcoal in medium is detrimental as it accumulates salts on its surface, and paph roots that come into contact will suffer root burn. I think this is tue. Often, when I repot paphs, I find that the charcoal has white deposits on it, and this often occurs with paphs that require lime (brachys). Should I keep using charcoal..? Please advise.. Thanks..

 

[Rick]

Karst is just a general term for any porous, cave, geology with limestone as the base material. Its not specific to any particular type of limestone. Karst is the predominant geology for Kentucky and Tennessee but there are numerous types of limestone with different chemical properties within the region. This also holds for the karst locations in Vietnam, China, Malaysia, and Borneo where our favorite paphs come from. Averyanov has a good recent article on the preference of the types of limestone preferred by P. emersonii vs. P hangianum in the karst areas of Vietnam.

I think a lot of people use charcoal with good results. It may depend more on the quality of the water you use as to whether it will load with salts faster than any other material. I use charcoal and can't claim any significant bad effects to it, but I water with RO water that is salt free.

I also use better grades of charcoal (activated carbon) for treatment processes in my lab, and I get very little (if any) adsorption of salts into carbon.

Some forms of calcareous materials such as dolmitic limestone and zeolite have significant ion exchange properties. Zeolite in particular is used as a water softening agent since it will adsorb calcium and release sodium so it is a poor choice of material to use in orchid media. Dolomite is usually good about releasing calcium and buffering pH.

 

[Eric Muehlbauer]

Now, I'm not a geologist...but my understanding is that "karst" refers to eroded limestone bedrock. While limestone bedrock originated as marine deposits, it is not necessarily derived from coral, nor would there be any salts at this point. "Karst" topography is found in many areas of the world, including the major paph growing regions of China and Vietnam. I think karst can be based on dolimitic rock as well as limestone. As for charcoal, I think its probably beneficial in small amounts, in media that is frequently changed. As most of us repot paphs within 2 years, frequently more, regardless of medium, I think a small amount of charcoal would be harmless, at least. Take care, Eric

 

[Roth]

I use charcoal, and so far no problems... The very best sanderianum I have seen grown in Miri, Sarawak were for years in big pieces of charcoal, a few chunks of coconut on top, and very, very hard tap water. The owner used the GrowMore fertilizers ( the easiest of the US/Canadian ferts to get in Asia...), but not actually the way we would do normally. 1 tablespoon monthly at the base of the plant for each 30cm pot. Of course it is the powder fertilizer, that normal beings dissolve in water...

For the article by Averyanov regarding emersonii var. huonglanae and hangianum, I must say I have been disappointed. The study has, by far, not been completed. The difference between those two species habitats is not "dolomitic limestone crystalline vs karst", but an issue with manganese, zinc, nickel and cobalt...

 

[Rick]

For the article by Averyanov regarding emersonii var. huonglanae and hangianum, I must say I have been disappointed. The study has, by far, not been completed. The difference between those two species habitats is not "dolomitic limestone crystalline vs karst", but an issue with manganese, zinc, nickel and cobalt...

You are correct that there was no mention of specific elements, but my point was that there are many forms of limestone (with different mineral properties) that are all "karst" formations.

 

[NYEric]

Yes, keep using the charcoal it is filtering the salts.

 

[Ron-NY]

the grit that they sell for raising chickens is what I use in my mix Calcium chips