Oyster Shell Calcium

Actually, thanks for bumping this.

More on topic: I've heard crushed egg shells can also be used as a calcium source. Is this true? Also that if you use epsom salts in rain or RO water for any reason (I tried once because I heard it can sometimes reverse yellowing) you should also use calcium supplement.

What else would you use epsom salts for?

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-Sara
Addicted and loving it.

Yes crushed eggshell work also. They and oystershell and small limestone all provide some buffering of pH in the mix. Dolomitic limestone contains some magnesium as well as calcium. All are slow acting. Calcium nitrate is quick and the nitrate is good also. Magnesium sulfate also suppiles a little sulfur along with the Mg. Rough proportion is 2:1 or 3:2 - CA:MG Both help the plant to produce chlorophyll. If you mix the two don't put them in solution at high concentration. You can get a preciptate of Ca SO4 (gypsum). When dissolving fert I use 1/4 teaspoon normal fert + 1/8 t. of Calcium nitrate per gal. after that is dissolved then I add a little less than 1/8 t. of the epsoms salt and mix again. Often you can find Calcium Nitrate (small BB sized pellets)in 50 lb quantities for landscaping fert or used as an additive to concrete to keep it from freezing when pouring in cold weather.

i know this is an old thread but just to add my 2 cents. there are many orchids occuring in nature in various types of limestone habitats, including many paphs. at my nursery we have turned to the oyster shell as it lasts longer than other forms and still gives some lime initially as well. i put a little in the mix but moreso use it as a topdress on the pots, this way you can see when its gone and add more. ive found in little experiments (with paphs) that the limestone is indeed beneficial in root production if nothing else. on sanderianums and phillipenense's that were put into the same mix with added oystershell and without, 6 monthes later, upon checking root health the limestone that had been washed down into the pots was all adheared to the roots and the roots of these plants seemed much more vigorous than those without..

hi
not only paphs need calcium
many more to......

Just to revive a dead topic. I also keep reef tanks, and we stopped using dolomite years ago. If I had to take a guess, I'd say that some of the larger substrates we use in reef tanks would be great to use with orchids, something like the cheap bags of large crushed coral would probably be good all around for any orchids that might use calcium. Plus the larger pieces in the cheap crushed coral will also be great for helping with drainage. Just make sure you rinse it well... actually, would probably do better to soak it for a good while just to make sure any remaining salts are out. I'd imagine the easiest way to do it is would be the same way we 'cure' homemade "live rock"... put it in the back of your toilet for a few weeks. Any salts will leech out, then when ever you flush; insta-water change.

Anywhos, just my 2 cents.