Although Jim is right in stating that potassium sulfate is more or neutral that does not exclude a change in pH. It strongly depends on what is used first or fastest. If the potassium is used fastests the soil will acidify , if the sulfate is used fastest the soil will become alkaline. An example: depending on the nitrogen source the pH in a petridish with fungal grow will turn acid neutral or basic. If ammoniumsulfate is ued the agar turns acid , if Sodium nitrate is used the agar turns alkaline , if pepton is ued the agar stays more or less neutral. I would not use a single salt, choose a well balanced mix suitable for what you wants i.e with high nitrogen for growth or low nitrogen for flowers and ripening Ben J.M.Zonneveld Institute of Biology,Leiden University, Clusius lab Wassenaarse weg 64, 2333 AL Leiden, The Netherlands Zonneveld@rulbim.Leidenuniv.NL Fax: +31-71-5274999. min temp -10C (15F)