Hi all, Roger and Arnold have provided some excellent information on this subject. What distinguishes potassium chloride from potassium sulfate is chemical composition, and the relative biological effects of the chloride vs the sulfate ions. Both are soluble sources of potassium. Industrial grades of either may contain traces of other materials. Chloride is the combined form of the element chlorine, and it is essential to most living things, but in limited amounts. Higher levels of it are toxic, and what those levels are specifically depends on the species of plant under discussion. "Muriate" is an archaic term for chloride and is not used in the modern scientific literature. You can look it up in any good dictionary of the English language. Just as we avoid vernacular names for plants, we would also do well to avoid using them for chemicals. Sulfate provides the element sulfur, which is also essential for all living things. It occurs in proteins as the amino acids methionine and cysteine. It can play a role in the transfer of methyl groups in biosynthetic processes. Potassium chloride is cheaper than potassium sulfate or potassium phosphate, and is likely to be found in cheap fertilizers as a source of the element potassium. It isn't advisable to use any fertilizer containing chloride on plants that have any sensitivity to chlorine. More expensive, higher quality fertilizers will not contain much chloride. Jim Shields AB in chemistry PhD in biochemistry ************************************************* Jim Shields USDA Zone 5 Shields Gardens, Ltd. P.O. Box 92 WWW: http://www.shieldsgardens.com/ Westfield, Indiana 46074, USA Tel. ++1-317-867-3344 or toll-free 1-866-449-3344 in USA