during flushing the plant is doing everything the same as it was, its just now breaking down all the chemicals you gave it throughout the grow and using up its stored nutrients, the tri's should be maturing just the same as they have been. 3 weeks is alittle early for a flush, also depending on your nutrients, most organics break down immediatly, and most chem ferts take a week to break down, this just helps with the curing process and good smoke, are you flushing or are u just cutting the nutes at 3 weeks, there is a difference, check out the flushing thread i think zandor or latewood made its a sticky so look it up.