Both very good questions, lets start with flushing.
The idea of flushing is that minerals or assimilates are somehow reduced in the flowers of cannabis. The flushing process removes the salts from previous fertigations to create a solution which is practically only water.
As it stands, flushing is not supported by any scientific theory or hypothosis, in which suggests that the flushing process can reduce the quantity of minerals in plants. Minerals go through a biogeochemical cycle, which goes through several successive chemical transitions. For example nitrogen is continually being recycled from plants to animals to decomposition back to the earth. Although these minerals can be assimilated into organic components, the minerals are still there. They are virtually indestructable compared to organic substances, such as vitamins which are volitile under specific temperatures.
The only workable process i know of is the effect of mineral deficiency on organic components, such as chlorophyll. However any of the natural processes that occurs due to these reasons, also occurs during the drying and curing stage, which to me with my experience, has the biggest effect on taste and burn than anything else. No matter what kind of feeding process the plants go through, a bad drying and curing process will always smoke worse compared to a good one.
Now with darkness before harvest. Much like the other question, there has been no evidence or theory which suggests leaving plants in darkness before harvest is beneficial.
Plants store their energy produced during the day from photosynthesis, mostly as sucrose and starch. Starch is stored in two ways, as transitory starch and stored starch. Cannabis does not store any significant long term starch, as its only a anual plant under the angiosperm family which does not genetically anticipate surviving past reproduction. As such, the only form of storage it has, is from transitory starch which is only short term and holds only enough photosynthates to last the duration of the night cycle. Exactly. I say exactly because plants utilize this transitory energy efficiently, by applyling simple biological mathematics to ensure that 95% of the excess energy produced during the day, is used by the time light arives. Even if the light cycle changes. So this stored resource is very limited, and under the typical 12/12 cycle, would be completely exhausted after 12 hours of dark. After which any duration longer than 12 hours is going to cause the plant to starve itself, and undergo the same processes that is done with plants harvested and drying. Just a lot slower.
