you harvest depends on the high you want
a good time to harvest with a good mix of high is about 10-20% amber (thats when you cut down the plant)
you start to flush atleast 2 weeks before you cut down the plant
the longer you flush the cleaner your buds will taste

using a true organic setting you really dont have to worry about flushing much because you dont have the excessive salt build up and it was the benneficials microherd feeding the plant

good luck