final flush

Hello rollitup users, I was wondering when I should start my final flush before harvest? My fan leaves are starting to yellow and I'm still giving her nutrients, I'm in the 8th week of flower and I'm growing in coco so I would like to flush for about a week. I would say about 70-80% of pistils...

For example, if I added orange extract to the res during the final flush, would the buds taste citrus-y at all? If essential oils wouldn't work, what about e-juice flavorings? I can't see them harming the plant in any way, unless they cause the plant to dehydrate or are toxic to it, but in...