After a very long ass time of not logging in on this site, and months of reading these very volatile flushing arguments, I have decided to weigh in.
Whether you flush or not is completely up to you.
1. PH is not a problem. Until it becomes a problem. Then it is a real fucking problem. If the water you are using is ph'd at 8.5+ that is a problem. PH your water down to neutral or buy distilled water.
Lime has a PH of 8.5+. Most soil starts out acidic. As it ages and activates it raises in PH. Using Lime helps a lot in the beginning but can cause problems if overdone at the end.
For a very long time, my tap water was neutral. At some point they switched wells and when they did, my water jumped up to 8.5 ph. I had tons of issues until I broke out my ph meters and realized my water had changed. (I used to be like trousers and that other dude and since everything was fine didn't try to "fix it"). Once things broke, it took me awhile to figure out my issue because I wasnt using a ph meter.
So while there is truth to what they are saying, at the same time they couldn't be more wrong. Just because they have good water running through good soil doesnt apply to everyone and if you dont occassionally check your PH you won't realize it until your leaves turn yellow/brown and start dying and it damned near happens overnight.
Back to flushing....
Someone earlier said they grew 2 plants, smoked them, couldn't tell any difference. I find that to be rather subjective.
Generally, in my experience, I can grow 2 clones of the exact same strain at the same time and I can tell a slight difference between the two plants. So to say there was no difference is kind of hard to believe. Even grown the same way, fed the same way, flushed (or not) the same way, there is generally a slight difference in two plants.
If you take something like oranges. Grow a tree in Cali, grow one in Florida, eat one, a few days later eat another. They will both taste like oranges. If you take a bite of the Cali orange, followed immediately by a bite of a Florida orange, there will be a distinct and very noticeable difference.
Hard for me to believe that if you cut a plant from nutrient depleted soil and one from nutrient rich soil that they will smell/taste exactly the same. Impossible for me to believe really. I AM NOT SAYING one is better than the other. Either or both will be really good.
While I do believe (and experienced) plants uptaking what they need and leaving what they don't to some extent, that would not fit to explain how a plant gets nutrient burned. If that was a stable rule, then a plant would never get nutrient burned. I use my own version of "super-soil" but light and only at the very bottom of the planter.
Now, as far as "scientific facts" go... well in some way this MIGHT apply to flushing...
There is a direct correlation in nitrogen levels and thc levels in hemp (many more hemp studies than cannabis at this point but certainly applies).
**** The HIGHER the levels of nitrogen in the soil at the end of flowering the LOWER the THC levels are *****
so if your objective is to grow nice green lush leaves, then by all means keep that nitrogen rolling through to the end..
If you are like me, and grow for the best possible bud quality (not quantity) you will want to get your nitrogen levels very low the last couple of weeks and when your plant is chopped, plenty of yellowing.
*Side Note* Nitrogen is needed for a plant to process phosphorus, if you have grown properly up to the last couple of weeks you have plenty of nitrogen stored in the leaves for this process which is why they turn yellow.
Now, just so happens that nitrogen is the easiest nutrient to flush from soil. This I know by having my soil tested at three seperate points at my local co-op to see the nutrient levels.
The last and final point before I log back out...
I have seen and heard people talk about "flushing stresses your plants". Pretty sure it is just people mocking what was said by Jorge Cervantes in his grow bible. After thousands of grown plants, 100s flushed and 100s not flushed, I am very curious how it is that a "stressed" plant has immediate bursts of growth? When I flush my plants, it never fails, within 24 hours I have a new burst of green sugar leaves and white pistils. In every other "stress" situation I have seen a plant in, growth stunts.... But you know, someone said it so it must be true....