When to flush the flower?

i run a flush for almost 3 weeks before my harvest time, so if the plant is a 9 week flower i start at the middle of week 6. if the plant is a 8 week flower i start at the beginning of week 6, i flush good for a week with water at room temp. after that i start flushing using water that is cold and has been in the refrigerator, i use the cold water to get any color that the strain may have, i use just cold water until the chop, this shocks the roots and gets great color from dark purples to lighter purples ,sometimes blues show, it really works and the colors do come out, for me flushing is just as important as getting those buds nice and big, and the smoke is pretty tasty and smooth

Only flush it if you have a heavy toxicity. Otherwise flushing is a pointless step that just harms your final flowers. Conventional wisdom is 2 weeks before harvest (2 days for hydro). I'll point out that conventional wisdom is wrong though. 2 weeks before harvest will probably be when about 70% of your pistils are red.