To be totally honest with you all, Ive been doing the dark/cold water thing for 5 years now. Not every plant I do goes thru this process since I've grow perpetual most of the time and have done this with quite a few strains. Ive done it with about 25 plants. I used to flush for the last ten days. Then harvest. My Purps still wouldnt burn right after curing for about 3 -4 weeks. It was still burning alittle black and was a bitch to keep lit in a zig-zag. So I started flushing for 2 weeks. This helped alot and the color was rapidly coming out of the leaves and turning bright yellow. I noticed that if I flushed them until all the color was gone in the top 1/3 of the plant leaves, then the weed was just perfect for smoking after 1 week in a jar. ((Obviously 3-4 months in a jar curing would be ideal but I dont have this luxury of sitting on my harvest that long.))
So anyways, 1 week in a jar and the joint burns very nice. The ash is white. The weed stays lit most of the time. and it just tastes and burns suppurb. Once I snap off a fan leaf, if it tastes bitter, the plant needs more flushing. If it tastes like nothing, like tap water, then its ready for harvest. After 3 weeks in a jar the weed is perfect for smoking. This is due to the flushing for 2 weeks. 14 days of flushing every 4 days. Thats 5 flushes before harvesting. The chloraphyl in the leaves is almost gone at this point. This is when the weed burns best for me and my strains.
This trick doesnt add any new trichomes but adds to the already existing trichomes. The trichs get much fatter. They seem to swell up like fat little mushrooms. I used to use CO2. I spent around 1200 bucks for the whole setup. I havent used co2 in the last 4 grows so Im loosing 25% - 20% of yield but the dark/cold water technique will add 20%-30% more girth to the trichomes. So this helps when trying to get the most from your plants if you dont have an elaborate grow-op. Most people have basics and thats it. I just happen to have an elaborate set-up but I just cant use it all here so I got to make the best with what I can use. This just helps alot anytime Ive done it. The weed is better than it wouldve been had I flushed for 7 - 10 days and harvested.
This is my experience. 2 each his own. Good luck with whomever this may have helped. PEACE.