Edger and others, please don't use abrasives to clean stems unless absolutely necessary. I have suggested, many times (as I don't have buffing wheels), the use of Flitz polish, first.
It is non-abrasive, non-toxic, acid-free, eco friendly and approved by the USDA. Apply lightly with a cotton cloth, work it in with vigor, polish with a clean soft cotton cloth. If a few attempts don't provide a satisfactory cleaning, you may then consider an abrasive. I find Mr. Clean Magic Eraser, although abrasive, used lightly, gets the green out. I then again apply Flitz, and finish with a dab of Obsidian oil. Hope this helps.