If ur whole grow has been organic there is no need to flush. Flushing is for ppl that use nutes which r salt based, like the FF grow big and tiger bloom r both salt based aka chelated metals EDTA, but the Big bloom is an organic product that uses kelp, guano, stuff like that. When u use those salt based nutes u get a build up of salts in ur plants, more so if its hydro, less if its soil or a similar medium that acts as a buffer. So when u flush ur plants a couple weeks before harvest it is to flush out all those salt deposits that have built up in ur plant so u get a better flavor from ur smoke once dried and cured.