i usually wait till about 50-75% of the pistils have turned and then i start to flush. The first flush i only give them about 3-4g per 5 gallon bucket. Then when it is time to water again i hit em with about 6-7g per 5g bucket. About the time they r redy to be watered again i give em a nice big flush with about 7-10g and really clean em out. then when the soil is nice and dry i give em a 24-48hr dark period and then harvest. I like to start off slow with the flush and give the plant time to use up everything it can; because idealy if u could u should fertilize right up until harvest. I like to do organics and i find it helps to add alot of bacterial innoculant to the flush water so that it will break down anything that may left in the soil.