Quote:
Originally Posted by shule1
Some potassium sulfate is supposed to be approved for organic gardening, but some of it is not.
The AlphaChemicals kind claims to be approved for organic gardening, but I tried to check it out and I didn't find anything in my search to prove that it was. Nevertheless, I got some from them on Amazon and some from them on eBay. The eBay product, although less expensive, had dark particles in it in addition to the potassium sulfate. The Amazon kind looked very pure (and was very effective). I haven't used the eBay kind as much, but it seems to work. I'm not sure what the dark stuff in it is.
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Potassium Sulfate is mined from natural deposits. Difference in color of particles is due to the purity of the final product. Not going to make much difference in applying powder or granules to garden soils, but if you were going to use it in liquid form you would want a very pure solution grade powder.