the vanatrol is really designed for removing concrete stains, try using bleach. Dilute with water and test in a small area on the flagstone before cleaning the whole walk. good luck.

Have you tried a pressure washer?

Hi - I know this thread is 7 yrs old, but I have this problem as well with a patio I have just installed (Arizona flagstone, colors like buff, oak, peach) where part of it is under a large redwood tree. The redwood berries stain the flagstone and the stains cannot be removed (I have tried everything - power washing, various cleaners, strong solvents, etc). The only way to get rid of the stains is by scraping off a layer of the stone (which, though very laborious, actually works, using a utility knife as recommended by my stone mason). I am now sealing with Glaze-N-Seal impregnator stone sealant and plan to do 3 coats for the area under the redwood trees. But I am pretty worried about this so if anyone has any ideas, experience or solutions in this area, let me know. I am happy to update with my results after sealing, if anyone else out there cares...

This post was edited by dave94010 on Wed, Jul 31, 13 at 17:32

Did this work Dave?

cephillips and/or Dave — did anything work? Did sealing help? We are having the same problem with a large redwood and newly installed bluestone patio.