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 Limestone Chipings

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PostSubject: Limestone Chipings   Thu Jul 17, 2008 10:27 pm

Does anyone out there use limestone chippings in there compost mix. The reason for asking is at the UK Mamm Society AGM the other week one of the members spoke about limestones chippings and now some growers have been adding it either to their compost mix or using it has a top dressing for some species of Mamm's such as the fine white spined plants.
A number of Mamm' grow in out crops of limestone and in Gypsum (high Ph levels). The theory being that by adding the limestone chippings you are raising the pH to it what would be in habitat. Never tried it myself but if anyone has done so then I would be interested to hear about now the plants have got on.
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PostSubject: Re: Limestone Chipings   Thu Jul 17, 2008 10:30 pm

I also have heard that this is done. In habitat a lot of plants do grow in limestone areas, especially those from Puebla.
I have not tried this myself, although I did buy a bag of limestone chippings a while ago, but never got round to using it, mainly because I don't know how uch to use. The question of pH values has been debated a lot, and for a while I used to use a compost that was designed for lime hating plants as my basis, together with grit. But that seemed to have more peat or similar, and so I changed to ordinary John Innes which has some lime in it. I can't say I have seen any noticeable difference.
I went to Mexico in 2005, and especially in Puebla there was a lot of limestone. The plants, such as M. haageana, M. mystax, M. sphacelata, M. carnea, grew there in abundance. But always they had found a gap in the substrate, or grew in an area, where a fair amount of vegetable matter had collected. So there is a balance then between the natural acidity of decaying vegetable matter, and the water that has filtered through the limestone, although there would be some direct water from rain as well.
It is possible therefore that the natural acidity of the actual material in which the roots have gained a hold acts as a buffer to the alkali effect of the limestone fuelled water, in which case I'm not sure there's a lot of point in trying to mimic it.
If you use a slightly alkali potting mix, and water with slightly acid rainwater, I think you end up in a similar situation, without the need to add any additional limestone. And there are different form sof limestone, which seem to dissolve in slightly acid water at different rates, so unles syou really know what is happening, I think its best to leave well alone - so long as your plants are growing OK.

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PostSubject: Re: Limestone Chipings   Thu Jul 17, 2008 10:32 pm

I have found an article in an old Mamm journal (1987) were the author had visited Mexico and while there done some Ph tests in habitat and he mentions 5 sites in this article..
Queretaro/San Luis Potosi road, M.gigantea and M.sanluisensis. pH6.6 - 7.
Zacatecas/Agus Calientes border. M.uncinata and M.gilensis. pH 7
Queretaro/Leon road. M.pygmaea. pH 6.5 - 7
Tilapa nr Techacan. M.crucigera. pH 8.5. M.sphacelata below.
Zapotitlan. M.haageana, pH 8.
I belive Reppenhangen took soil samples of some of the habitats he visited. Does anyone know if he ever got around to doing pH tests on the samples?
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PostSubject: Re: Limestone Chipings   Thu Aug 07, 2008 9:15 pm

Back in the '90s I tried using limestone chippings for white-spined mamms and others. I used a layer at the bottom of the pots, which is what the person advocating this reccommended. The chips were fairly big - over 10mm. I can't say I noticed any improvement and the roots didn't make a bee-line for the chippings. In fact the compost at the bottom of the pots seemed a bit sour when I came to repot plants, and I gave up the idea.
Having said this, I watered using tap water, which is very hard in our area. I am of the opinion that it is better not to worry too much about the chemistry of the compost (unless you know what you are doing) and to repot fairly regularly.
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