# DIY substrate and limestone



## Andy Thurston (11 Aug 2013)

One for the science boffins...
I came across this article earlier today​ 
Understanding Plant Nutrition: Limestone, Calcium And Magnesium - Greenhouse Grower Website - Greenhouse Grower - Article

I know that john ines 3 contains ground lime and I assume it is garden lime but could be wrong. Although I don't fully understand the science bit and soils react different when submerged but am I right in thinking that the Mg in the limestone can be used by the plants?
Also while reading about DIY substrates I've read that people add dolomite lime, osmocote and clay to peat/pond soils etc. I understand that clay is added for CEC and as an iron source, and osmocote for NPK.  So is the dolomite lime added as a source of Mg and could this be of benefit in my tank and reduce the need to boost the gh of my water?


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## dw1305 (11 Aug 2013)

Hi all,


Big clown said:


> Also while reading about DIY substrates I've read that people add dolomite lime, osmocote and clay to peat/pond soils etc. I understand that clay is added for CEC and as an iron source, and osmocote for NPK. So is the dolomite lime added as a source of Mg and could this be of benefit in my tank and reduce the need to boost the gh of my water?


Yes that is correct, dolomite is limestone where some of the CaCO3 has been replaced by MgCO3 (you can tell by colour, ground limestone looks like cement dust (mainly because cement dust is mainly ground limestone), but dolomitic limestone is "pink" in colour ). You don't really need dolomite, "Epsom Salts" are another source of Mg with a lot more Mg content. 


Big clown said:


> I came across this article earlier today


Commercial growers like sphagnum peat based composts because they have no nutrients and a very low pH, the advantage of this is that you start from a blank canvas, and you know exactly what you have added. A 100% peat based compost could be used with a very weak liquid feed to grow Blueberries or epiphytic Orchids, but add enough fertiliser and lime to the same mix, and you could grow Tomatoes or Cabbages.

cheers Darrel


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