WHY: The idea behind flushing is to let your plants âuse upâ any extra nutrients contained in the plant and buds. This way there is a much lower level of nutrients left over after harvest, and itâs those extra nutrients that can change the smell, taste, or (most often) âsmoothnessâ of your buds in a negative way. WHEN: Wait until the plant already looks like itâs at the early end of the harvest window, in other words, wait to start the flush until you could pretty much harvest the buds right now if you wanted.HOW: Provide only plain pHâed water to plant until harvest (from a few days to 2 weeks)