I have no clue on all of the technical terms but roots dont just take up whatever you give them, this is why all of those BS products in grow shops call "berry fever" or "mint manic" dont work. Putting vanilla extract into your water isnt going to do anything good for your plant, i would even bet it would do more harm than good. Just to de-rail the stupidity of this ill mention flushing is a fruitless effort that does nothing but make your plant hunger for the nutrients it needs the most in those last few weeks. The only common sense reason to flush these days is the thought that cheap chemical nutrients build up salts, which if they do you would see noticeable effects in your plant and if you are really gun-hoe on flushing then do it two waterings before you chop, you cant just magically wash the salts away if they are already there.